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An Epidemiological Analysis of Dengue in Argentina Cecilia Radkiewicz 12 credits, 11th semester Supervisors: Åke Lundkvist, professor, Institutionen för Mikrobiologi, Tumör och Cellbiologi, (MTC) Karolinska Institutet María Cristina Diumenjo, MD, Departemento de Bioestatística, Ministerio de Salud, Universidad Nacional de Cuyo

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Abstract 3 Introduction 4 Aetiology, the dengue virus 4 Clinical features 5 Treatment 6 The vector, Aedes aegypti 6 History and Geographic Distribution 8 Material and Methods 10 The site of the study 10 The surveillance system 13 Dengue surveillance 13 Case classification 14 Laboratory investigations 14 Prevention 15 Out-break plan 15 The low-risk province, Mendoza 15 The high-risk province, Salta 16 Results 19 The Salta province 19 Seasonal variation 19 Sex distribution 21 Age distribution 21 Geographical distribution 22 Argentina 23 Discussion 24 References 26

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An Epidemiological Analysis of Dengue in Argentina Cecilia Radkiewicz 12 credits, 11th semester Supervisors: Åke Lundkvist, prof, institutionen för mikrobiologi, tumör och cellbiologi, Maria Cristina Diumenjo, MD, departemento de estatistica, universidad nacional de cuyo Abstract Objective To make an epidemiological analysis of dengue (2002-2007), in the Salta province in detail, and Argentina in general. Background The emergence of dengue has been dramatic in South America, the cause is complex and not well understood.1 A. aegypti, the main vector, was eradicated in Argentina in 1963 but has partly re-infested the country. In 1997 the first cases of dengue in Argentina since 1916 were detected in Salta.2,3 Methods The intranet of the national surveillance system in Argentina coordinates and presents epidemiological dengue data collection.4 The intranet was employed to gather the necessary statistical material. Results 613 laboratory confirmed cases of dengue fever (DF) and three cases of dengue haemorrhagic fever (DHF) were reported. All DHF cases were reported in Salta in 2007. The seasonal distribution showed a peak in the summer. Both sex and all age groups were affected. In Salta 13 operative areas were affected, the majority identified as high risk areas. Conclusions This analysis suggests that dengue is on the way of becoming endemic in northern Argentina. If governmental organizations do not take immediate actions to prevent the ongoing development there is an impending risk that dengue in Argentina in general and the in Salta province in particular is on the way to becoming a major health problem.

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Introduction The global incidence of dengue has increased dramatically during the last decades and dengue is currently classified as an emerging or re-emerging infectious disease by the WHO. Dengue fever (DF) and dengue haemorrhagic fever (DHF) occur in over 100 countries, with more than 2.5 billion people at risk and an estimated 50-100 million cases per year. The major disease burden is found in south-east Asia and the western Pacific, with increased reporting of DF/DHF especially in the Americas.5 Aetiology, the dengue virus DF and DHF are caused by a flavivirus, an enveloped virus, with an icosahedral capsid and a single-stranded, linear, non-segmented, positive polarity RNA. The flaviviruses include dengue, hepatitis C, yellow fever, West Nile, and St. Louis and Japanese encephalitis viruses. Dengue virus circulates as four immunologically distinct serotypes with large genetic diversity (DEN-1, DEN-2, DEN-3, and DEN-4). Despite this diversity dengue fever normally displays a typical clinical picture. Infection with one serotype provides lifelong immunity to that specific serotype, but only transient immunity to the other serotypes.6 The dengue genome encodes a single large open reading frame that is translated to form a viral polyprotein. The polyprotein is subsequently cleaved in the cytoplasm by viral and host proteases to produce three structural and seven non-structural (NS) proteins. The structural proteins are named C (capsid), PrM/M (pre-membrane/ membrane), and E (envelope).7

Two electron images of mature DEN-2 particles replicating in five-day-old tissue culture cells. The original magnification is 123,000 times.8

Adaptive immunity (antibodies and cytotoxic T cells) is very important in the prevention of viral diseases. The first exposure to a virus, symptomatic or asymptomatic, stimulates production of antibodies and activation of cytotoxic T cells. Adaptive immunity plays an essential role in protecting against disease when exposed to the same virus in the future. The duration of protection varies. Lifelong protection against systemic viral infections is a function of the secondary IgG response. The role of adaptive immunity in recovery from an acute viral infection is often uncertain, since recovery usually precedes the appearance of detectable humoral antibodies. An important phenomenon is original antigenic sin. This means that when a person is exposed to a virus that cross-reacts with another virus to which that individual was previously exposed, more antibody may be produced against the original virus than against the current one. This may yield misleading antibody titres but is also one of the underlying causes of severe dengue hemorrhagic shock. The pathogenesis is as follows: The patient recovers from classic dengue fever caused by one of the four serotypes, and antibody against that serotype is produced. When the patient is infected with another serotype, a heterotypic response occurs, and large amounts of cross-reacting antibodies to the first

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serotype are produced. There are two major hypotheses about what happens next. One is that immune complexes, composed of virus and antibodies, are formed and activate complement, causing increased vascular permeability and thrombocytopenia. The second one is that the antibodies increase the entry of virus into monocytes and macrophages with the consequent liberation of a large amount of cytokines. In either scenario, shock and haemorrhage is the result.6 The dengue virus is an arbovirus mainly transmitted by the Aedes aegypti mosquito, which is also the vector of yellow fever virus. Humans are the major reservoir, but a jungle cycle involving monkeys as reservoir and other Aedes species as vectors are suspected. The life cycle of arboviruses is based on the ability to multiply in both the vertebrate host and the bloodsucking vector. For effective transmission, the virus must be present in the bloodstream of the vertebrate host (viremia) sufficiently to be taken up in the small volume of blood ingested during an insect bite. After ingestion, the virus replicates in the gut of the arthropod and then spreads to other organs, including the salivary glands. An obligatory length of time, called the extrinsic incubation period (the intrinsic incubation period refers to the interval between the time of the bite and the appearance of symptoms in the human host) must pass before the saliva of the vector is infectious. Usually humans are dead-end hosts, because the concentration of virus in human blood is too low and the duration of viremia too short for the next bite to transmit the virus. However, in some diseases, e.g. yellow fever and dengue, humans have a high-level viremia and thereby act as reservoirs of the virus. The diagnosis (see following chapters) can be made in the laboratory either by isolation of the virus in cell culture, by serologic tests that demonstrate the presence of virus specific IgM antibodies or a 4-fold or greater rise in antibody titres between the acute and the convalescent sera, or by molecular biology test (PCR).6 Clinical features Dengue infection can produce a spectrum of clinical illness, from a non-specific viral syndrome to severe and fatal hemorrhagic disease and shock. Symptoms appear 3-14 days (average 6 days) after the bite of an infected mosquito. Risk factors for developing severe disease include the strain and serotype of the virus, chronic diseases, age, immune status and genetic predisposition of the patient, but also prior infection with another serotype.9 DF is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death. Infants and young children may have a non-specific febrile illness with rash. Older children and adults may have either a mild febrile syndrome or the classic “break bone fever” with abrupt onset of high fever, severe headache, infraorbital pain, myalgia, arthralgia and rash. DHF is a potentially fatal complication that is characterized by high fever, haemorrhagic phenomena (such as petechiae, microscopic haematuria, epistaxis, bleeding gums, haematemesis or melaena), liver enlargement and circulatory failure (mainly due to capillary plasma leakage). It begins with a sudden rise in temperature and other non-specific constitutional DF symptoms. The fever (sometimes biphasic) may reach 40-41°C and usually continues for two to seven days. In moderate DF cases symptoms subside after temperature is normalized. In severe cases the temperature drops after a few days of fever and the patient may rapidly go into a critical state of circulatory failure and shock, dengue shock syndrome (DSS), and die within 24 hours.8 Important differential diagnoses are chikungunya fever and other viral fevers transmitted by arthropods, but also influenza, measles, rubella, malaria, leptospirosis, typhoid, and systemic viral fevers, especially those associated with coetaneous manifestations.10

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Treatment There is still no DF vaccine available, although there are several tetravalent live-attenuated dengue vaccines in clinical phase I or II trials. Neither does any DF specific treatment exist, the only therapy available is symptomatic. Therapeutic-based processes are being investigated and the development of new potential drugs with molecular viral targets is emerging.11 DHF patients should be monitored concerning platelet count (falling), haematocrit (rising) and signs of shock (deterioration, lethargy, restlessness, acute abdominal pain, cold extremities, skin congestion or oliguria), since about one-third develop DSS. The critical period usually occurs after the third day of fever when the temperature starts to normalize. The major pathologic process is increased vascular permeability leading to loss off fluid from the vascular compartment. If uncorrected this may lead to shock, tissue anoxia, metabolic acidosis and death. Apart from the vascular changes mentioned, DHF also exhibit thrombocytopenia and disorders of coagulation. This may lead to disseminated intravascular coagulation (DIC) which can cause bleeding (mainly from the gastrointestinal tract) and play a major role in the development of a refractory lethal shock. Early and effective replacement with plasma expander or fluid and electrolyte solution in combination with adequate correction of metabolic and electrolytic disturbances rapidly reverses DHF/ DSS.12 High fever, anorexia and vomiting may result in dehydration, oral fluid intake is usually sufficient. During the acute febrile phase there is a risk of convulsions, antipyretics (for example paracetamol) can be used for high risk patients (positive history). Salicylates must be avoided since they can enhance bleeding and cause acidosis, but also trigger Reye syndrome.11 There are data suggesting that administration of dipyrone (NSAID) in patients with DF is associated with decreasing platelet counts and an increased risk of developing DHF.13 Blood grouping and matching should be carried out for every patient in shock, though blood transfusion (preferably fresh full blood) is only indicated when significant clinical bleeding. Fresh frozen plasma or platelets may be indicated in DIC cases or where coagulopathy causes bleeding. Essential laboratory tests are; haematocrite, serum electrolytes, blood gas analysis, platelet count, prothrombin time, partial thromboplastin time, thrombin time and liver function tests.11 Some DHF cases develop acute hepatic failure with elevated aminotransferases and neurological symptoms. This is a bad prognostic sign and causes therapeutic problems since these patients must be given intravenous fluid with extreme caution to avoid brain oedema and encephalopathy.11 The vector, Aedes aegypti Dengue virus is transmitted to humans through the bites of an infective female Aedes mosquito (especially A. aegypti, but also A. albopictus). A. aegypti is also the principle vector transmitting yellow fever and chikungunya virus. Worldwide, this species has a range extending from 40°N - 40°S latitude and is found throughout most tropical to subtropical regions. Survival is poor in hot, dry climates. The mosquito acquires the virus from feeding on blood from an infected person in the febrile phase of the disease when the virus is circulating in the blood. Infected female mosquito may also transmit the virus to their offspring via their eggs, though the role of this has not yet been thoroughly investigated. After virus incubation for 8-10 days, an infected mosquito is capable of transmitting the virus for the rest of its life (4-30 days). Humans are the main amplifying host of the virus, although studies have shown that monkeys may also serve as a viral source.14, 15 A. aegypti is a day biting mosquito (highest activity early morning and late afternoon), that preferably resides in urban and semi-urban areas. Adult mosquito feed on flower nectar and juices of fruits for flight energy. The female requires a blood meal for egg development. Human blood is preferred and the ankle area is a favoured feeding site. A. aegypti only flies a few hundred

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yards from the breeding site. The life cycle consists of four separate stages: ovum, larva, pupa, and adult. Aedes species do not make egg rafts, like other mosquito species. The female mosquito deposits the eggs separately on damp surfaces, next to stagnant water. Preferred breeding areas are flower vases, uncovered barrels, buckets and discarded tires. The ovum may survive up to one year when dry and hatch within 48 hours when flooded with water, typically after rainfall. The ovum takes 5 days to develop into larvae, the larvae stage generally last for 5-14 days. The larvae feed on micro-organisms and organic matter in the water and come to the surface to breathe. Larvae die at temperatures below 10°C or above 44°C. On the fourth molt the larva changes into a pupa, a resting, non-feeding stage. This is when the mosquito turns into an adult. Adults are killed by temperatures below freezing and do not survive well at temperatures below 5°C. The length of the different stages depends on the surrounding environment conditions (nutrition, temperature and humidity). On average, females live up to a month and males die sooner.13, 14

A. aegypti is a medium-sized (approx. 0.5 cm) blackish mosquito easily recognized by a white pattern of scales on its scutum and white rings on segment 1-4. The coloration of both sexes is similar.

Monitoring Several indices have been used to measure larval densities, such as the number of water receptacles containing larvae (container index), or the total number of receptacles with A. aegypti larvae per 100 houses (Breteau index). Often a container index greater than 20, or a Breteau index above 5 indicate that the vector population has reached a level which presents a threat of urban transmission of yellow fever.16 History In the eighteenth century slave ships from West Africa to the Americas carrying casks of drinking water, providing breeding places for A. aegypti, aided the spread of the mosquito into the New World. The extended global spread of the mosquito is facilitated by a rapid urbanization accompanied by an unreliable water supply and domestic water containers providing a perfect habitat for A. aegypti.15 A. albopictus is a native of South-East Asia where it commonly breeds in discarded tyres. Like other Aedes species eggs can tolerate months of desiccation and then hatch when soaked by rainwater. In 1979 A. albopictus suddenly appeared in Albania and in 1985 in Texas, USA. It has also been introduced into Mexico, South America, Fiji, Italy, Nigeria and a few other countries. It was brought to these countries as dry viable eggs mainly in used exported tyres.15 In the1940s and 1950s an A. aegypti eradication programme in Latin America freed 19 countries. But the mosquito was not eradicated from all countries and in the 1970’s the programme deteriorated. In 1995 the distribution of A. aegypti in Latin America was almost identical to that of the 1940s.15 In Argentina the mosquito has been detected in 332 municipalities, from Buenos Aires and the Pampas in the south stretching all the way to the northern border.9

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Problems and difficulties Water-storage containers cannot be discarded since they provide essential domestic water. Covering with plastic mosquito screening counteract ovi-positioning but still allow the containers to be filled with rainwater. However, in practice it is notoriously difficult to get communities to cover such potential breeding places. In Puerto Rico, in the 1980s, after comprehensive educational propaganda, more than 70% of the people considered dengue an important disease and about 70% also believed that dengue could be prevented. Nevertheless, it proved impossible to get the community to change their habits. There are many more examples illustrating the difficulties to get full and sustained community cooperation. Though, in Cuba, when Fidel Castro declared A. aegypti “The Public Enemy Number One” the entire community cleaned up the environment, removing discarded bottles, tin cans, and other mosquito breeding places. Similarly, in Singapore, people helped to eliminate A. aegypti breeding places around their houses, because householders could otherwise be fined or imprisoned. Consequently Singapore and Cuba have the most efficient A. aegypti control programmes in the world. Despite many disappointments and failures, most national and international health agencies believe that the only long-term solution to controlling dengue in Asia and the Americas is through community participation.15 Environmental measures, such as physically preventing A. aegypti from breeding in domestic water containers, are preferable. But, if a dengue epidemic is threatening the lives of people, the only rapid response is insecticidal spraying to kill infected adult mosquitoes. Once the epidemic is under control there can be a return to a more integrated approach to vector control. However, the situation has to be constantly monitored for detection of any re-introduction.15 History and geographic distribution The first reported dengue epidemics occurred in 1779-1780 in Asia, Africa, and North America. Until the mid-twentieth century DF only occurred infrequently as major epidemics in tropical regions. Nowadays dengue is endemic in the majority of the tropical countries.17 The global spread started in Southeast Asia following World War II. The epidemiology changed because of ecological transformations (domestic water storage, transport of war equipment and soldiers, left over war material) which increased larval habitat for A. aegypti and enabled transport of mosquitoes and their eggs to new geographical areas but also human transport of virus strains to susceptible populations. This resulted in high densities of A. aegypti and hyperendimicity (co-circulation of multiple strains of dengue virus) which facilitated the first real emergence of DF and DHF in Southeast Asia. An unsurpassed urbanization and population growth, involving inadequate housing, water, sewer and waste management in this region contributed. In every Southeast Asian country the emergence of DHF evolved in a similar way, at first sporadic cases for several years, then culminating into outbreaks. From the mid 1950s to the 1970s epidemic DHF was localized to a few Southeast Asian countries. In the 1980s and 1970s a dramatic geographic expansion west into India, Pakistan, Sri Lanka, the Maldives and east into China took place. Even in Singapore, with an outstanding prevention and control program, there was a resurgence of DHF, mainly because of a low herd immunity and virus import via migrant workers. Today Asia suffers from cyclic DF and DHF outbreaks every 2nd - 5th year.16

The dengue surveillance in Africa has been poor and still is, when epidemics occur they are often reported as malaria outbreaks. In spite of this, laboratory confirmed dengue-epidemics have increased dramatically since 1980. Limited outbreaks have occurred in West Africa, but also in East Africa and in the Middle East. All four virus serotypes have been involved, but only sporadic cases of clinical DHF have been reported.16

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Map: Dengue distribution in the world, 2006. Blue areas: Aedes aegypti infestation. Red areas: Aedes aegypti and recent dengue epidemics.18

Epidemic dengue re-emerged in the Americas in the late 1970s. Before this there was no epidemic activity due to a successful A. aegypti eradication programme initiated by the Pan American Health Organization (PAHO) in 1946 to prevent yellow fever. In the early 1970s the programme was discontinued and by the end of the 1980s the countries that achieved eradication were re-infested.16

Map: Aedes aegypti re-infestation in the Americas, 1970 and 2002. PAHO/WHO, 2002

This coincided with movement of dengue virus both into and within the region. From the 1950s to early 1980s there was non-endimicity (no virus) or hypo-endimicity (only one serotype) in most American countries. In 1977 DEN-1 was introduced to the region via Jamaica and Cuba, and subsequently spread into the Caribbean islands, Mexico, Texas, Central America and Northern South America, causing major or minor epidemics over the next four years. In 1981 DEN-4 was introduced and spread rapidly in a similar way. Some of the outbreaks were associated with the first documented cases of DHF in the Americas. In 1981 a new strain of DEN-2 was introduced in Cuba, most probably from Southeast Asia. This caused the first major DHF epidemic in Cuba and was associated with thousands of cases of severe DHF. Epidemic DHF of variable intensity caused by the same strain of DEN-2 has subsequently occurred in numerous American countries, but none with the same severity. In 1994 a new strain of DEN-3, also from Asia, caused a major DF/DHF epidemic in Nicaragua and subsequently spread throughout Central America and Mexico causing major outbreaks. The changing epidemiology of dengue in the Americas in the 1970s to the 1990s is almost identical to the development in Southeast Asia in the 1950s to the 1970s. The re-invasion of Aedes aegypti in combination with increased urbanization and movement of people has resulted in an increased epidemic activity and the emergence of DHF. Cuba, Venezuela,

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Brazil, Colombia and Nicaragua have had major DHF epidemics, but only small DHF numbers have emerged in the rest of the American countries.16 Today dengue is endemic and cause cyclic outbreaks in almost the hole of the Caribbean and Latin America, including Bolivia, Brazil, Colombia, Ecuador, French Guyana, Guyana, Mexico, Paraguay, Peru, Suriname, Venezuela and Central America.9

In northern Argentina several cases of dengue were reported in 1905-1911 and in 1916 an outbreak of 15,000 cases were reported. In 1955 A. aegypti covered a large part of Argentina, reaching Buenos Aires, but by 1963 the mosquito was considered eradicated. In 1997 the first dengue cases since 1916 were confirmed.19 The mosquito has been detected in 332 municipalities from Buenos Aires and the Pampas in the south stretching all the way to the northern border.9 In 1998 a dengue outbreak occurred in the province of Salta, in total 644 cases of dengue was laboratory confirmed. This was the first time dengue was laboratory diagnosed and the virus isolated (DEN-2) in Argentina.20

Material and Methods The site of the study Geography and Climate Argentina is situated in southern South America, between the Andes in the west and the Atlantic Ocean in the east. It is bordered by Paraguay and Bolivia in the north, Brazil and Uruguay in the northeast, and Chile in the west. Its total area is approximately 2.7 million km². Consequently, Argentina is the second largest country in South America (after Brazil) and the 8th largest country in the world. Argentina is nearly 3,700 km long from north to south, and 1,400 km from east to west (maximum values). The geographic coordinates are 34°00’S, 64°00’W. The terrain can roughly be divided into four parts: the fertile agricultural plains of the Pampas in the centre, the flat to rolling and oil-rich plateau of Patagonia in the southern half down to Tierra del Fuego, the subtropical flats of the Gran Chaco in the north, and the rugged Andes mountain range along the western border. Argentina displays a variety of climates, but is predominantly temperate with extremes ranging from sub-tropical in the north to sub-Antarctic in the south. The north of the country is characterized by very hot, humid summers with mild drier winters, and suffers from periodic droughts. Central Argentina has hot summers with thunderstorms and cool winters. The southern regions have warm summers and cold winters with heavy snowfall, especially in the mountains. Higher elevations at all latitudes experience cooler conditions.21 The province of Salta is situated in north-east Argentina. It is bordered by Bolivia and the province of Jujuy in the north, Paraguay and the provinces of Formosa and Chaco in the east, the provinces of Santiago del Estero, Tucumán and Catamarca in the south, and Chile and the province of Jujuy in the west. Its total area is approximately 155 488 km². The geographic coordinates are 22°00’N, 26°23’S, 62°21’E, 68°33’W. The climate is tropical but displays distinct variations between the different regions. The mountain chain has an important influence on the precipitation. The eastern part is semi-dry, annual precipitation 500 mm, the temperature ranging from -5°C up to 47°C (average 20°C). The mountain plateau is characterized by brusque changes in temperature (average 10°C) and sparse rainfall, annual precipitation 200 mm. The fertile valleys are densely populated and have a humid climate suitable for agriculture, annual precipitation reaching 1000 mm, average temperature in summer 20°C and 14°C in winter. The A. aegypti infestation is abundant, with a peak during summer months (December to March). The population is approximately one million inhabitants. Almost half of the population live in Salta capital, Orán or Tartagal, which are the

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most densely populated municipalities. The Salta province is a communication node between the north of Chile, the north-east of Argentina, Bolivia and Paraguay. There is a constant and intense movement of people and merchandise across the border to the neighbouring countries. Bolivia and Paraguay have both suffered from several severe dengue outbreaks in the last years.22

Map: Climate Map of Argentina. Gobierno Electrónico Argentina. Available from: http://www.surdelsur.com/argentinamap/climatemap.htm

Population (in thousands) total 38747 (2005) Total fertility rate (per woman) 2.3 (2005) Population annual growth rate (%) 1.1 (2005) Population in urban areas (%) 90.0 (2005) Population living below the poverty line (% living on < US$1 per day) 7.0 (2003) Gross national income per capita (PPP international $) 13920 (2005) Total expenditure on health as percentage of gross domestic product 9.6 (2004) Adult literacy rate (%) 97.2 (2004) Life expectancy at birth (years) men 72.0 (2005) women 78.0 (2005) Population with sustainable access to improved drinking water (%) urban 98 (2004) rural 80 (2004) Population with sustainable access to improved sanitation (%) urban 92 (2004) rural 83 (2004)

Table 1. Core Health and Socioeconomic Indicators23

Inequities in Health24 Argentina is not only extremely diversified when it comes to geography and climate. It is also a country with a severe disparity between rich and poor, urban areas and countryside, and displays major differences in development between the central provinces and the remote northern parts. The figures in Table 1 are all correct but do not give a fair picture. The northern, subtropical provinces; Chaco, Corrientes, Formosa, Misiones, Jujuy and Salta are in high risk of future dengue epidemics. These provinces also have the smallest margin and lack sufficient financial resources to combat a feasible epidemic. They fall behind development in several important areas. This is neatly illustrated by the statistics in Table 2-3. Table 2

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displays socio-economic indicators, comparing the situation in the whole country, Buenos Aires city (BA) and the Northern provinces. The Human Development Index (HDI) measures the average achievements in a country in three basic dimensions of human development; a long and healthy life (life expectancy), knowledge (literacy and education) and a decent standard of living, for countries worldwide. It is used by the United Nations Development Programme in its annual Human Development Report to determine whether a country is developed, developing, or underdeveloped.25 The mean HDI for Argentina and BA is high (0,800-1) while the northern provinces only reach a medium (0,500-0,799). Another multidimensional measure of poverty is Unsatisfied Basic Needs (Necesidades Básicas Insatisfechas NBI). The Argentine government uses the following strategy to characterize households with unsatisfied basic needs:26

1. Overcrowded homes is households with more than three persons per room. 2. Unsuitable housing. Housing is considered unsuitable if it is a tenement or some other

poorly built house, apartment, or shack. 3. Houses without toilets. 4. Households with children aged 6-12 years not attending school. 5. Survival capacity. Households which have 4 or more working members as well as

those households whose head of household has not completed third year of primary education.

Only 7.8% of the households in BA, but almost a third of the households in the poorest provinces does not have one or more of the basic needs satisfied. 1. 2. 3. 4. 5.

Argentina 0,826 17,7 2,6 77 42,5

Buenos Aires city 0,892 7,8 0,5 99,9 96,6

Corrientes 0,772 28,5 6,5 81 42,4

Chaco 0,755 33 8 61,6 18,6

Formosa 0,764 33,6 6 64,7 21,7

Jujuy 0,772 28,8 4,7 92,6 48

Misiones 0,772 27,1 6,2 57,2 11,3

Salta 0,792 31,6 4,7 89,9 51,1

Table 2. Socioeconomic Indicators 2003.23 1. Human Development Index (HDI) 1996. 2. Households with at least one NBI (%) 2001. 3. Adult illiteracy rate (%) 2001. 4. Population with sustainable access to improved drinking water sources (%). 5. Population with sustainable access to improved sanitation (%).

A. B. C. D.

Argentina1 4,4 16,5 10,5 0,7

The central region2 2,6 15,2 9,4 0,5

The north-west region3 7,6 19,1 12,6 0,8

The north-east region4 8,2 23,2 15,7 1,3

Table 3. Maternal and Child Health 2003. 23 A. Maternal mortality rate (per 10.000 live births). B. Infant mortality rate (per 1000 live births). C. Neonatal mortality rate (per 1000 live births). D. Under-5 mortality rate (per 1000 live births). 1The whole country. 2Buenos Aires city and province, Cordoba, Entre Rios, Santa Fe. 3Catamarca, Jujuy, Santiago del Estero, Salta, Tucuman. 4Corrientes, Chaco, Formosa, Misiones.

Table 3 compare indicators concerning maternal and child health. Development, i.e. public health, is falling behind in the northern provinces. The actual dengue prevention programme is based on vector population control. The cornerstones of this programme are public health education and communication, and improvement of the sanitary environment (see following chapters). Subsequently, a region falling behind in development will face major difficulties combating a feasible dengue outbreak. The living standards in the Salta province are poor when comparing to the central provinces, as well as the general level of education. A significant part of the population lack sustainable access to improved drinking water and sanitation. Also a large proportion of the population

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are descendants to indigenous people. These people commonly live segregated from the rest of the population in so-called Misiónes. The litteracy rate is low and malnutrition is common. The grave poverty as well as cultural differences in these neighbourhoods, contribute to the difficulties the public health care system meet. The surveillance system (Sistema Nacional de Vigilancia Epidemiologica SiNaVE) Dengue surveillance in Argentina is organized as a collaboration of the National Department of Epidemiology, National Ministry of Health, Provincial Departments of Epidemiology, National and Provincial Departments of Vector control, and the DENV laboratory network.27 A compulsory report program, a disease specific form and laboratory procedures for several diseases, among them dengue, are essential components of the surveillance system. (See attached form Notificación Médica Obligatoria C2) SiNaVE is organized into four levels;

1. Population; all inhabitants of Argentina. 2. Local health care professionals in direct contact with the population. 3. Provincial Departments of Epidemiology collect, compile and forward the information

reported by the local physicians. 4. The National Department of Epidemiology summarize, draw up national guidelines,

and forward epidemiological data to international organizations (WHO and PAHO).28 Dengue surveillance Information and instructions on the surveillance, prevention, and control of dengue are distributed to health care professional at all health care establishments (public as well as private). Case classification and information about the procedures and investigations that must be performed on suspected cases are disseminated to physicians at all levels. When identifying a suspected case, every physician is obliged to;

1. Immediately contact the provincial epidemiological department by telephone or fax. 2. Obtain the laboratory tests needed. 3. Complete the specific designed form containing personal information, clinical signs,

laboratory tests performed, and epidemiological data on the suspected case.29 (See attached form Vigilancia de Sindrome Febril B1-3).

DengueNet is an international surveillance system created by the WHO to improve global dengue surveillance. It is a central data management system made to collect and analyse standardized epidemiological and viral data, and present epidemiological trends. The American region was the first to participate. The objective is to provide public health authorities and the general public with immediate real time data on dengue morbidity and mortality as well as circulating virus serotypes.30 Due to the major dengue outbreak in the neighbouring country Paraguay in January 2007, the Argentine National Ministry of Health declared an alert epidemic situation. The Northern provinces (Formosa, Misiones, Corrientes, Chaco and Salta) bordering Paraguay and Bolivia and A. aegypti infested are at especially high risk. High risk provinces must monitor all febrile cases and the following measurements and recommendations were reinforced;31

- Intensified surveillance of all febrile conditions. - Registration and epidemiologic investigation of all suspected, probable and confirmed

dengue cases. - Focal control and/or block of viral transmission. - Evaluation of the efficiency of the intervention programme. - Intensified vector control at a provincial level.

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Case classification28 Classical dengue fever (DF), ICD-10: A90 A suspected DF case is defined as an acute febrile illness no longer than seven days, characterized by frontal headache, and showing at least two of the following symptoms; retro-ocular pain, muscle and joint pain, coetaneous rash, minor bleeding phenomena immobilisation, nausea or vomiting, in combination with residence or movement into an area with confirmed dengue transmission. A Probable DF case is a clinically compatible case with supportive serologic findings such as single acute or convalescent-phase serum positive for Immunoglobulin (Ig) M antibody or a dengue virus IgG antibody titre ≥1280. A confirmed case is a clinically compatible case that is laboratory confirmed either by virus isolation, IgM seroconversion or a four-fold increase in IgG titres for paired serum, or molecular biology test (PCR). Dengue haemorrhagic fever (DHF), ICD-10: A91 A clinically compatible DF case presenting one or more of the following haemorrhagic manifestations;

1. Positive Tourniquet (capillary fragility test) 2. Petechiae, ecchymoses or purpura 3. Gastrointestinal or mucosal haemorrhage (gingival bleeding, haematemesis, melaena) 4. Thrombocytopenia (≤100x109/l) 5. Plasma leakage, due to increased capillary permeability, causing one or more of the

following characteristics; - 20% increase of haematocrit (adjusted for age). - 20% decrease of haematocrit after rehydration therapy, (compared to basal level). - Pleural effusion, ascites or hypoproteinaemia.

Dengue haemorrhagic shock syndrome (DSS) A DHF case presenting symptoms or signs of circulatory failure; fast and weak pulse, reduced pulse pressure, hypotension (age adjusted), cold extremities, restlessness or agitation. Laboratory investigations28

1. Isolation of dengue virus from serum and/or or autopsy tissue samples (confirmed). 2. Demonstration of a four-fold or greater rise or fall in reciprocal IgG or IgM antibody

titres (MAC-ELISA) to one or more dengue virus antigens in paired serum samples (confirmed).

3. Detection of dengue virus antigen in autopsy tissue by immunohistochemistry or by viral nucleic acid detection (confirmed).

4. Detection of dengue virus genomic sequences in autopsy tissue, serum samples, or cephalo-rachidial liquid using polymerase chain reaction (PCR) techniques (probable).

Serum samples (≥ 5 ml, if possible 10 ml) should preferably be collected from suspected cases 5 days (late acute) and 10-20 days after onset of symptoms (convalescent). When using serological methods for diagnosis it is important that the corresponding epidemiological history accompany the sample to the laboratory. The usage of anti-coagulants must be avoided, as well as deep freezing, unless the sample can not be sent to the national reference laboratory within 4 days. The laboratory result for specific antibodies is ready within 72 hours, PCR within 48 hours, and virus cultivation takes about 15 days.32 The DENV laboratory network is coordinated by the national institute for human viral diseases (Instituto Nacional de Enfermedades Virales Humanas, INEVH), the national

15

reference centre of DENV diagnosis in Argentina.26 To guarantee true verification of suspected cases additional support was distributed to the DENV laboratory network (laboratorios de la Red), including equipment and instructions on how to collect, handle and process dengue diagnostic samples. Standardized protocols were designed to secure sufficient diagnostic quality and a reliable sample referral chain.33 Prevention34 1. Public health education and communication on methods how to eliminate, destroy and control the vector mosquito (i.e. A. aegypti) larvae habitat, that is to say artificial water containers inside or close to housing (water receptacles, vases, old tyres, and groceries). 2. Community studies to assess vector density and recognise major larvae habitats, with the objective to speed up programs on how to eliminate, control and combat the mosquito. 3. Personal protection against mosquito bites; repellents, mosquito nets, and adequate clothing. Out-break plan35 Four different epidemiologic situations and four corresponding contra-actions can be outlined. In the first scenario a probable case is identified in an area with no vector infestation, this demands for an epidemiological investigation. In the second scenario A. aegypti is present but indigenous dengue is not (Mendoza), a probable dengue case then causes an alert epidemiologic situation and calls for active measures at community level. In scenario number three there are several probable cases in a mosquito endemic area, an epidemic (Salta). This requires active measurements as well as serologic surveillance to detect new serotypes. The fourth situation is “worst case scenario” where hyperendimicity (more than one serotype circulating) is present and dengue is endemic.34 Active measures at the individual level involve.33

- Epidemiological (activities last 15 days before debut) and laboratory investigation. - Report to local health authorities. - Avoid patient-mosquito contact until the fever has subsided. - Active look-out for unreported or undiagnosed cases. - If DF appears in Yellow Fever (YF) endemic areas, YF-vaccination is recommended.

In case of an epidemic, the local government must act to locate and kill adult mosquito near housing, and to protect people exposed to mosquito bites;

- Information, education and communication to the general public, concerning mosquito biology, virus transmission and prevention.

- Intensified surveillance of febrile cases in high risk areas. - Intensified control of mosquito breeding ground. - Elimination of mosquito breeding ground through destruction or inversion of water

containers, larvae repellents, or elimination of adults. - Campaigns to eliminate crocks and improve municipal waste management.27

The low-risk province, Mendoza The following section is based on an oral presentation and a personal interview with Dr. Horacio Falconi (e-mail: zoonosismendoza@yahoo.com.ar phone: +54 261 5091772) the responsible veterinary at the Division for Zoonosis, Reservoirs and Vectors (División de Zoonosis, Reservoires y Vectores) in the Mendoza province.

16

Several approaches to improve the sanitary environment to combat the mosquito vector and inhibit viral transmission exist. Environmental modifications involve improvement of public access to drinking water and sanitation, as well as elimination of natural vector reservoirs. Manipulative methods include covering reservoirs with mosquito net and improving community consciousness to prevent human vector contact (physical barriers, repellents). Another aspect when discussing preventive measurements is to subdivide methods into natural or chemical. Natural methods are preferable;

- Sustainable access to improved drinking water (water supply and storage). - Sustainable access to improved sanitation. - Improved garbage management, including; yards, houses, lots, streets, dustbins, etc. - Modification of other man-made breeding ground, such as; farm basins, enclosures,

posts, tarpaulins, wash basins, etc. - Personal protection, e.g. adequate clothing, mosquito nets, etc.

A chemical approach must be rational and strategic to avoid mosquito resistance to insecticides, ecologic changes affecting other species, and unwanted human effects;

- Focal control is limited to larvae habitat and consists of organic phosphor insecticide granules placed in artificial water containers.

- General control methods aim at adult mosquito and involve spatial spraying of ultra low volume (ULV) of a pyrethroid insecticide 400 meters around case location blocks.

- Sub-focal control is aiming at larvae habitat as well as adult mosquito. ULV indoor spraying is limited to mosquito infested households of suspected cases.

Biological control methods, yet not applied in large-scale, are fresh-water fish feeding on larvae (Gambusia and Poecilia species), competitive larvae, hormones, water fleas, and bacteria (Bacillus species). In Mendoza preventive actions are based on public education. An impressive educational material on how to eliminate larvae habitat, vector biology and lifecycle, and dengue symptoms, has been prepared. Pedagogical material, including a CD ROM computer game, is handed out to teachers at primary schools. Written information is distributed to primary health care professionals performing home visits. Due to economic limitations, the use of other mediums (newspapers, radio and television) does not exist. Entomologic surveillance in Mendoza is only implemented during summer months (e.g. January till May). These investigations are basic and the objective is to determine A. aegypti presence in the province. Water-filled tyres are placed in appropriate surroundings and checked for mosquito egg, larvae or pupae every week. If a suspected dengue case appear in Mendoza the patient is highly recommended to accept hospital admission where patient-mosquito contact can be strictly under control. If this is not possible, the Division for Zoonosis, Reservoirs and Vectors will investigate if the affected household and block must be subject for a general chemical control programme. The high-risk province, Salta The following chapter is based on a study visit at the municipal Department of Epidemiology, Hospital Juan D. Peron in Tartagal, the Salta province and circulating letters of directions (Circular Normativa) provided by Dr. Josefina Aguierre, chief at the local Department of Epidemiology in Tartagal, published by the Ministry of Public Health in the Province of Salta;

EPI 5 Sitios centinela para la vigilancia epidemiologica de dengue EPI 7 Vigilancia entomológica de Aedes Aegypti EPI 8 Uso de repelente en pacientes y convivientes de casos sospechosos de dengue EPI 12 Dispositivo para recipientes no descacharrables EPI 19 Guia para la utilización del Spinosad y Glifosato para el manejo de Aedes Aegypti EPI 20 Uso del hipoclorito de sodio contra huevos de Aedes Aegypti

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The objectives of the surveillance system are intensified epidemiological surveillance of all cases of acute febrile illness and early detection of any cases compatible with dengue (see previous chapters) as well as early identification of circulating serotypes. The Salta province is divided into operative areas;

1. Operative areas in high risk of DF and DHF. (orange) 2. Operative areas in high risk of DF. (yellow) 3. Operative areas in moderate risk of DF. (green)

Map: The Salta province, operative areas. Orange: operative areas in high risk of DF and DHF. Yellow: operative areas in high risk of DF. Green: operative areas in moderate risk of DF. (EPI 5)

1 Colonia Santa Rosa O 13 Rivadavia Banda Sud O 25 San carlos 37 Guachipas

2 Pichanal O 14 Las Lajitas Y 26 Molinos 38 El Potrero

3 Aguaray Y 15 J.V. Gonzalez Y 27 Cachi 39 Urundel O

4 Morillo O 16 El Quebrachal 28 General Mosconi O 40 Hospital San Bernardo G

5 Santa Victoria Oeste 17 El Galpón G 29 Los Andes 41 Hospital del Milagro G

6 Inya 18 Rosario de la Frontera G 30 Cerrillos G 42 Hospital Christofredo

7 Salvador Mazza O 19 Metán G 31 Hipólito Yrigoyen O Jackob

8 Santa Victoria Este O 20 Hospital Materno Infantil 32 Rosario de Lerma G 43 Hospital Endocrinologia

9 Embarcación O 21 La Candelaria 33 Chicoana y Metabolismo

10 Nazareno 22 General Güemes G 34 El Carril G 44 Alto La Sierra

11 Orán O 23 Apolinario Saravia O 35 Coronel Cornejo 45 PNA- Area Capital G

12 Tartagal O 24 Cafayate 36 La viña 46 Hospital “El Milagro” G Salta Province, Operative Areas. (EPI 5)

Anticipatory surveillance phase Serum samples for viral isolation should be collected from suspected cases 3 days after onset of symptoms, and sent to the National Reference Laboratory (INEVH in Pergamino) within 72 hours, accompanied by the dengue specific form. In case of an outbreak and when the circulating serotype has been identified, confirmation of suspected cases should be carried out by testing for IgM antibodies instead of viral isolation. Serologic samples are sent to the

18

provincial laboratory (Laboratorio de Virologia del Hospital Milagro) (see previous chapters). Local pharmacists are instructed to report increasing consumption of the most commonly used antipyretics. Surveillance during the high risk period (Nov-May)

- Daily notification of suspected cases tested negative. - Weekly epidemiological report in case of an outbreak. - Weekly report of housing and Breteau index (A. aegypti infestation), the objective is to

keep the housing index < 1%. A fixed number of households are selected and larvae presence is controlled weekly (Nov-May) or monthly (Jun-Oct). (EPI 7)

Once an outbreak is officially announced, IgM samples are collected from one out of five of the suspected DF cases and from every single suspected case of DHF. Communication All probable DF cases detected during the anticipatory surveillance phase must be reported immediately to the chief of the Epidemiologic Surveillance Programme: Dr. Griselda Rangeón or her subordinate Dr. Alberto Gentile. Daily notification, by fax or telephone, of suspected cases tested negative starts on the first of November every year. In case of an outbreak in an operative area the weekly epidemiological report is sent by e-mail or fax to the Epidemiologic Coordination Committee (Dirección de Coordinación Epidemiológica). Control actions All suspected cases and co-inhabitants must be informed on how to use mosquito repellent by their physician. Individuals ≥ 2 years are advised to use a 23.8% DEET (N,N-diethyl-m-toluamide) spray, individuals ≤ 2 use a special customized alcohol free essence. Suspected cases must use repellent up to and including day four and co-inhabitants up to and including day 12 after symptom onset (EPI 8). Detection of probable and confirmed cases leads to immediate and urgent actions to find compatible cases in the same household and neighbourhood. Simultaneously, actions to verify the entomologic situation in every single household in the neighbourhood are made (EPI 7). This is also an opportunity to inform the neighbours to seek medical advice and to avoid aspirin in case of acute febrile illness. The problem how to discard water-storage containers which serve as mosquito breeding places has been subject to many discussions. But it has proved difficult to change human behaviour. In the Salta province, sanitary agents work preventive by visiting people in their homes, handing out information and showing potential risks in the surrounding environment. Despite many disappointments community participation is the only long-term solution to control A. aegypti (EPI 12). Spinosad insect spray (a mixture of two naturally occurring metabolites, spinosyns A and D, produced by S. spinosathe) is used to control adult A. aegypti. Glyphosate (N-(phosphonomethyl) glycine), is an herbicide used to constrain mosquito preferred mating areas (EPI 19). Sodium hypochlorite (NaOCl), commonly known as bleach, is placed in dry containers before watering to prevent A. aegypti ovipositioning (EPI 20). Responsibility

- Management of diagnostic laboratory samples; provincial (Laboratorio de Virologia del Hospital Milagro) and national (INEVH, Pergamino).

- Vector Index Reports: The Department of Zoonosis and Environment. - Daily reports of negative cases and weekly reports; The Epidemiologic Surveillance

Programme.

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Results Salta From January 2002, when SiNaVE first introduced the electronically surveillance system, to December 2007 the Provincial Department of Epidemiology in Salta reported 378 DF and 3 DHF laboratory confirmed cases to the National Department of Epidemiology. The incidence rate ranges from 0.28 to 15.6 cases per 100,000. All DHF cases were registered in 2007. Two outbreaks, in 2004 and 2007, occurred during the period studied (see Table 1).

Year 2002 2003 2004 2005 2006 2007 Total

N1 21 52 168 11 3 126 381

IR2 1,946155 4,819049 15,56924 1,019414 0,278022 11,67693 35,3088 Table 1. 1Number of laboratory confirmed DF and DHF cases reported to SiNaVE. 2Incidence rate (per 100 000 population). Salta 2002- 2007.

Seasonal variation There is a marked seasonal correlation between the number of registered DF cases and the temperature and precipitation (see Diagram 1-7). Most cases were reported between January and June with a slight peak in March. From epidemiological week 17 onwards the weekly report dropped, showing a probable halt in transmission. Effective transmission probably only occur over the first four months of the year (see Diagram 8). Diagram 1, weekly DF surveillance Salta 2002 Diagram 2, weekly DF surveillance Salta 2003

DF Salta 2002 (N=21)

0

1

2

3

4

5

6

7

8

9

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

Ca

ses

DF Salta 2003 (N=52)

0

2

4

6

8

10

12

14

16

18

20

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

Ca

ses

Diagram 3, weekly DF surveillance Salta 2004 Dagram 4, weekly DF surveillance Salta 2005

DF Salta 2004 (N=168)

0

2

4

6

8

10

12

14

16

18

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

Cas

es

DF Salta 2005 (N=11)

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

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ses

20

Diagram 5, weekly DF surveillance Salta 2006 Diagram 6, weekly DF surveillance Salta 2007

DF Salta 2006 (N=3)

0

1

2

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

Ca

ses

DF Salta 2007 (N=123)

0

5

10

15

20

25

30

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

Ca

ses

Diagram 7, weekly DF surveillance Salta 2002- 2007

DF Salta 2002-2007 (N=378)

0

5

10

15

20

25

30

35

40

45

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

Ca

ses

Sex distribution The distribution by sex did not show any predominance though the attack rate was slightly higher in females. The mean male:female ratio between 2002 and 2007 was 1:1,1. A great variation different years is observed, the ratio ranging from 1:3,2 in 2002 to 2:1 in 2006 (see Table 2).

Table 2. Number of DF cases per sex. Salta 2002- 2007

Age distribution The age distribution displays an extreme dispersion going from <1 to ≥ 65. The 15- to 24- year age group is slightly predominant, but since this is also the dominating age group in the population the incidence rate looks different (see Diagram 8). The age specific IR was highest in the 45- to 65- year age group, followed by the 35- to 44- year age group. (see Table 3).

Year Male (%) Female (%) Total (%) M:F ratio

2002 5 (23,8) 16 (76,2) 21 (100) 1:3,2

2003 24 (46,2) 28 (53,8) 52 (100) 1:1,2

2004 76 (45,2) 92 (54,8) 168 (100) 1:1,2

2005 6 (54,5) 5 (45,5) 11 (100) 1,2:1

2006 2 (66,7) 1 (33,3) 3 (100) 2:1

2007 69 (54,8) 57 (45,2) 126 (100) 1,2:1

Total 182 (47,8) 199 (52,2) 381 (100) 1:1,1

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Table 3. Number of laboratory confirmed DF cases reported to SiNaVE in different age groups. Salta 2002- 2007. Diagram 8. Age and sex distribution. Salta.

Salta, age and sex distribution

0

20000

40000

60000

80000

100000

120000

≤ 1 1 2 to 4 5 to 9 10 to 14 15 to 24 25 to 34 35 to 44 45 to 64 ≥ 65

Age group (years)

Po

pu

lati

on

Geographical distribution From January 2002 to December 2007, 13 of 46 operative areas in the Salta province reported laboratory confirmed dengue cases (see Table 4). Out of 13 operative areas 11 were identified by the Ministry of Public Health in the Province of Salta as being in high risk of DF and DHF. One, Aguaray (3), was identified as an operative area in high risk of DF and one, PNA- Area Capital (45), as an operative area in moderate risk of DF (see previous chapter). Affected Operative Areas 2002 2003 2004 2005 2006 2007 Total

Colonia Santa Rosa (1) R 21 21

Pichanal (2) R 13 13

Aguaray (3) Y 4 17 21

Morillo (4) R 3 3

Salvador Mazza (7) R 12 28 1 1 52 94

Santa Victoria Este (8) R 3 2 5

Embarcación (9) R 22 2 2 10 36

Tartagal (12) R 9 2 28 7 39 85

Rivadavia Banda Sud (13) R 6 6

General Mosconi (28) R 1 5 6

Hipólito Yrigoyen (31) R 9 1 2 12

PNA- Area Capital (45) G 4 1 5

Orán (11) R 70 1 71

Total 21 52 168 11 3 123 378 Table 4, number of laboratory confirmed DF cases reported to SiNaVE (per operative area), Salta 2002- 2007. R: Operative area in high risk of DF and DHF. Y: Operative area in high risk of DF. G: Operative area in moderate risk of DF.

Age group <1 1 2-4 5-9 10-14 15-24 25-34 35-44 45-64 ≥ 65 unspec. Total

2002 2 7 2 2 3 5 21

2003 1 1 3 10 9 11 9 2 6 52

2004 8 5 18 32 24 30 43 8 168

2005 1 3 2 1 4 11

2006 1 1 1 3

2007 4 10 12 29 21 11 20 6 10 123

Total 1 0 12 16 37 81 59 55 80 16 21 378

IR 3,69 0 15,2 11,8 30,6 39,3 40,2 46,6 51,1 24,6 35,0

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The majority of the operative areas reporting laboratory confirmed DF cases between 2002 and 2007 were affected in one or both of the 2004- and 2007-outbreaks (see Table 4). Salvador Mazza (7) and Tartagal (12) reported the highest number of DF cases and are also affected almost every year (see Map 1- 6). Map 1, affected operative areas, Salta province 2002 Map 2, affected operative areas, Salta province 2003

Map 3, affected operative areas, Salta province 2004 Map 4, affected operative areas, Salta province 2005

Map 5, affected operative areas, Salta province 2006 Map 6, affected operative areas, Salta province 2007

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Argentina

From January 2002, when SiNaVE first introduced the electronically surveillance system, to December 2007, 616 laboratory confirmed DF and DHF cases were reported to the National Department of Epidemiology. Overall, 3 cases of DHF cases were registered, all in 2007 in the Salta province. The incidence rate ranges from 0,022 (in 2006) to 0,71 (in 2007) cases per 100 000 population (see Table 5).

Year 2002 2003 2004 2005 2006 2007 Total

N1 21 58 255 11 8 259 616

IR2 0,057915 0,159955 0,703252 0,030336 0,022063 0,714283 1,698836 Table 5. Overall DF cases Argentina 2002- 2007. 1 Number of laboratory confirmed DF and DHF cases reported to SiNaVE. 2 Incidence rate (per 100 000 population).

Seasonal variation

The seasonal pattern in Argentina was similar to the Salta province. Most cases were reported in the first months of the year with a slight peak in the end of February and the beginning of March. From epidemiological week 17 onwards the weekly report dropped, showing a probable halt in transmission. A few cases were also reported in epidemiological week 39 to 49 (see Diagram 11). Diagram 11, weekly DF surveillance Argentina 2002- 2007

DF Argentina 2002-2007 (N=613)

0

10

20

30

40

50

60

70

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

Epidemiological week

Cas

es

24

Discussion In 2007, 259 DF and DHF cases were registered in Argentina, this is the highest annual number recorded since SiNaVE first introduced the electronically surveillance system. The same year the first DHF cases were registered. Close to half (N=126) of the DF cases and all (N=3) of the DHF cases in 2007 were registered by the Provincial Department of Epidemiology in Salta. Even though the numbers are small this indicates that dengue is increasing in Argentina and that the Salta province is in particularly high risk of dengue epidemics in the near future. The number of DF cases reported to SiNaVE demonstrates laboratory confirmed cases only. The actual number can therefore be considered to be higher. Another reason to believe that dengue incidence is underestimated is the fact that an unknown percentage of the dengue fever infections are asymptomatic or present atypical or light symptoms. Patients who do not seek medical advice are obviously not included in the statistics. In Salta a significant part of the population is indigenous people living under very poor conditions which contribute to a low report frequency (patient bias). Dengue fever can also be mistaken for other febrile conditions such as; malaria, yellow fever, leptospirosis, hantavirus infections, among others (doctor bias). The above mentioned biases are of unknown magnitude. In 1997 the first cases of dengue in Argentina since 1916 were detected in the Salta province. The time span between 1916 and 1997 (81 years) eliminates the suspicion that herd immunity could cause over- or under-diagnosis of dengue. The surveillance system is not optimal for analyzing incidence rates. When an outbreak is recognized and the circulating serotype identified, case confirmation is carried out testing for IgM antibodies instead of viral isolation. Once an outbreak is officially announced, IgM samples are only collected from one out of five suspected DF cases. It is simple to identify an outbreak and analyze the epidemiological pattern retrospectively but impossible to calculate the quantity. A dengue epidemic requires the presence of the vector mosquito (until today mainly A. Aegypti), the dengue virus (DEN-1, -2, -3, -4) and a large number of susceptible human hosts. Outbreaks may be explosive or progressive, depending on the density and efficiency by which the vector can be infected, the serotype and strain of dengue virus, the number of susceptible humans in the population, and the amount of vector-human contact.1 In the Salta province all these variables coincide creating a surrounding in high risk of severe outbreaks in the future. A. aegypti infestation is abundant. The vicinity to Bolivia and the concurrent movement of people across the boarder result in introduction of new dengue virus serotypes into a highly susceptible and previously unexposed population, a combiantion of low herd immunity and virus import via migrant workers. A significant share of the population lives under poor conditions in shantytowns without systems for running water or sewage. Gathering rainwater in receptacles is an essential part of everyday life. Together with the low educational level this give rise to great difficulties for governmental sanitary agents working preventive against dengue. A male predominance was expected since that has been shown in other studies36,37 and since men are more exposed to mosquito bites, a higher proportion working outdoors in the agricultural sector. When comparing farming to other occupations, a strong association with DENV prevalence has been shown in other studies.38 But the distribution by sex (male:female ratio 1:1,1) did not show any significant predominance. In contrary, the incidence rate was slightly higher in females. Other studies have shown that the dengue case fatality rate is higher in females.35 A hypothesis is that if women have a severe clinical picture and subsequently seek medical advice more often. This could explain the slight female predomination. The considerable variation observed between the different years, the ratio

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ranging from 1:3,2 (in 2002) to 2:1 (in 2006), could be a coincidence since very small numbers were reported the years with no autochthonous transmission. Outbreaks of dengue fever were found to occur seasonally during the summer months. The marked seasonal correlation between the number of registered DF cases and temperature and precipitation is explained by the mosquito life cycle, which requires hot and damp conditions to proceed (see previous chapter). Effective transmission probably only occurs over the first four months of the year. Cases recorded outside the summer season are most probably imported cases from other parts of South America where dengue is endemic all year round. The age specific incidence rate observed was highest in the 45- to 65- year age group, followed by the 35- to 44- year age group. All age groups were affected, ranging from <1 to ≥ 65. In other epidemiological studies, mainly implemented in Southeast Asia, the age-specific incidence rate was highest in the younger age groups; 5- to 9- and 10- to 19 years of age,39 15- to 29- years of age.36 In the Salta province the highest number of cases was found in the 15- to 24- year age group. But since this also is the largest age group the incidence rate is only 39,3 compared to 51,1 in the 45- to 64-age group. No complete explanation could be found for this discrepancy, but demographic differences, genetic vulnerability, and different DENV serotypes could be part of the answer. The Salta province is divided into 46 operative areas, 13 reported laboratory confirmed dengue cases between 2002 and 2007. The majority (N=11) of these operative areas were affected in one or both of the 2004- and 2007- outbreaks. The majority of the affected areas are fertile lowland where the climate is humid and suitable for agriculture, annual precipitation reaching 1000 mm, average temperature of 20°C in summer and 14°C in winter, and abundant A. aegypti infestation in the summer (December to March). The Ministry of Public Health in the Province of Salta identify 11 out of 13 affected operative areas as being in high risk of DF and DHF. One operative area, Aguaray (3), is identified as being in high risk of DF and one, PNA- Area Capital (45), as being in moderate risk of DF. The epidemiology in Southeast Asia has changed. Dengue was originally considered to be a rural problem, nowadays it has turned into an urban disease.36 Approximately 50% of the population in the Salta province live in Salta capital, Orán or Tartagal, which makes them the most densely populated municipalities. This could explain that densely populated high risk areas in the Salta province; Salvador Mazza (7) and Tartagal (12), have reported the highest number of DF cases and are also affected almost every year. This could also explain why PNA- Area Capital (45) was affected, despite being considered operative area in moderate risk of DF. Apart from climate conditions and population density the position plays a major part in the geographical distribution of dengue. The Salta province is a communication node between the north of Chile, the north-east of Argentina, Bolivia and Paraguay. There is a constant and intense movement of people and merchandise across the border to the neighbouring countries.21 Bolivia and Paraguay both suffered from several severe dengue outbreaks during the last years. The affected areas are all situated close to the Bolivian border or main country roads leading from the border to the major cities. The changing epidemiology of dengue in the Americas in the 1970s to the 1990s is almost identical to the development in Southeast Asia in the 1950s to the 1970s. In every Southeast Asian country the emergence of DHF evolved in a similar way, at first sporadic cases for several years, then culminating into outbreaks. Today Asia suffers from cyclic DF and DHF outbreaks every 2nd-5th year.16 In the Americas the re-invasion of A. aegypti in combination with increased urbanization and movement of people has resulted in an increased epidemic activity and the emergence of DHF. Cuba, Venezuela, Brazil, Colombia and Nicaragua have had major DHF epidemics.16 Today dengue is endemic and cause cyclic outbreaks in almost every country in the Caribbean and Latin America, including Bolivia, Brazil, Colombia,

26

Ecuador, French Guyana, Guyana, Mexico, Paraguay, Peru, Suriname, Venezuela and Central America.9 Today A. aegypti has the same distribution in Argentina as before the PAHO eradication programme.18 The mosquito has been detected in 332 municipalities from Buenos Aires and the Pampas in the south stretching all the way to the northern border.9 In 1998 a dengue outbreak occurred in the province of Salta. This was the first time dengue was laboratory diagnosed and the virus isolated (DEN-2) in Argentina.13 Since 2002, 616 laboratory confirmed DF and DHF cases have been reported to SiNaVE. Four provinces have reported autochthonous cases; Salta, Jujuy, Formosa and Misiones. 32 Several circumstances are suggesting that dengue is becoming endemic in South America and northern Argentina. The actual epidemiological pattern is practically identical to the development in Southeast Asia a couple of decades ago. Apart from rapid urbanization and population growth, involving inadequate housing, water, sewer and waste management, new factors affecting the epidemiology of dengue are becoming increasingly important. Global warming causing ecologic transformations increasing mosquito larval habitat, mosquito resistance to insecticides, increased travelling resulting in transport of mosquitoes and their eggs to new geographical areas but also human transport of virus strains to susceptible populations, and the spread of new mosquito vectors (A. albopictus) may also affect the outcome in an unpredictable direction. The conclusion is that if governmental organizations do not take immediate actions to prevent the ongoing development there is an impending risk that dengue in Argentina in general and Salta province in particular is on the way to becoming a major health problem. References 1 Center for Disease Control and Prevention/ National Center for Infectious Diseases. [homepage on the internet]. Colorado: Division of Vector Borne Diseases [updated 2005 aug 22, cited 2007 may 23]. Dengue fever. Available from: http://www.cdc.gov/ncidod/dvbid/dengue/index.htm 2 Aviles G, Rangeon G, Vorndam V, Briones A, Baroni P, Enria D, et al. Dengue Reemergence in Argentina. Emerg Infect Dis. 1999 Jul-Aug;5(4):575-8. 3 Aviles G, Rangeon G, Baroni P, Paz V, Monteros M, Sartini JL, et al. Outbreak of Dengue-2 virus in Salta, Argentina, 1988. Medicina (B Aires). 2000;60(6):875-9. 4 Aviles G, Paz M V, Rangeon G, Ranaivoarisoa M Y, Verzeri N, Roginski S, et al. Laboratory Surveillance of Dengue in Argentina, 1995-2001. Emerg Infect Dis. 2003 Jun;9(6):738-42. 5 World Health Organisation (WHO). Dengue and dengue haemorrhagic fever. Fact sheet No 117, revised 2002 Apr. Available from; www.who.int/mediacentre/factsheets/fs117 6 Levinson WE. Medical Microbiology and Immunology: Examination and Board Review. 8th ed. New York: McGraw-Hill; 2004. 7 DengueInfo.org [homepage on the internet]. Singapore: Genome Institute of Singapore (GIS) and Novartis Institute for Tropical Diseases (NITD); c2005 [cited 2007 Nov 26]. Available from: http://dengueinfo.org/NITD/index.html 8 Center for Disease Control and Prevention. National Center for Infectious Disease Control [homepage on the internet] Colorado: Division of Vector Borne Diseases. Dengue fever (updated 2007 Oct 19, cited 2007 Oct 24). Available from; www.cdc.gov/NCIDOD/DVBID/DENGUE/index.htm

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9 Lee MS, Hwang KP, Chen TC, Lu PL, Chen TP. Clinical characteristics of dengue and dengue hemorrhagic fever in a medical center of southern Taiwan during the 2002 epidemic. J Microbiol Immunol Infect. 2006;39:121-29. 10 Heymann DL, editor. El control de las enfermedades transmisibles. 18th ed. Washington: Organización Panamericana de la Salud; 2005. 11 Melino S, Paci M. Progress for dengue virus diseases. Towards the NS2B-NS3pro inhibition for a therapeutic based approach. FEBS J. 2007 Jun;274(12):2986-3002. 12 World Health Organization (WHO). Dengue haemorrhagic fever: diagnosis, treatment, prevention and control. 2nd ed. Geneva; 1997. p. 24-33. 13 Diaz-Quijano FA, Villar-Centeno LA, Martinez-Vega RA. Effectiveness of early dipyrone administration on severity of dengue virus infection in a prospective cohort. Enferm Infecc Microbiol Clin. 2005 Dec;23(10):593-7. 14 Ministerio de la Salud de la Nación. Enfermedades Vectoriales. In: Manual de Normas y Procedimientos del Sistema Nacional de Vigilancia Epidemiológica (Si.NA.VE.). Argentina; 1999. p. 90-92. 15 Womack M. The yellow fever mosquito, Aedes aegypti. Wing Beats. 1993 5(4):4. 16 Van Emden HF, Service MW. Pest and Vector Control. New York: Cambridge University Press; 2004. 17 Gubler DJ. Epidemic dengue/dengue haemorrhagic fever as a public health problem in the 21st century. In: Smith GL, editor. New challenges to health: the threat of virus infection. West Nyack, NY: Cambridge University Press; 2001. p. 247-269 18 S Department of Agriculture/ Agricultural Research Service. Dengue: An emerging arboviral disease. GG Clark. 2007. Available from; www.afpmb.org/meetings/TriService2007/Presentations/Monday/OClubMorning/TRIServiceDENemergingJAX2007.ppt 19 Segura EL. Emerging Infections in Latin America. In: Davis JR, Lederberg J, editors. Emerging Infectious Diseases from the Global to the Local Perspective: Workshop Summary. Washington DC: National Academies Press; 2001. p. 35-52 20 Ministerio de la Salud de la Nación. Enfermedades Vectoriales. In: Manual de Normas y Procedimientos del Sistema Nacional de Vigilancia Epidemiológica (Si.NA.VE.). Argentina; 1999. p. 90-92. 21 Central Intelligence Agency, office of public affairs. Argentina. In: The World Factbook 2007. Washington: Government Printing Office; 2007. 22 Ministerio de Defensa, Servicio Meteorològico Nacional. Estadìsticas Climatològicas Perìodo 1991-2000. Buenos Aires; 2003. Available from: http://www.camdipsalta.gov.ar 23 WHOSIS (WHO Statistical Information System). A Guide to Statistical Information at WHO, World Health Statistics 2007. Available from: http://www.who.int/whosis/en/index.html 24 Boletín del Programa Nacional de Estadísticas de Salud. Agrupamiento de causas de mortalidad por división político territorial de residencia, edad y sexo. Rep. Argentina. Año 2005. Dirección de Estadísticas e Información de Salud (DEIS). Ministerio de Salud. Presidencia de la Nacion. Available from: http://www.deis.gov.ar/Publicaciones/arbol_tematico.asp 25 UNDP.org [homepage on the internet]. New York: United Nations Human Development Reports; 2007 [cited 2007 Nov 15]. Available from: http://www.undp.org/ 26 INDEC.MECON.ar. [homepage on the internet]. Buenos Aires: Instituto Nacional de Estadística y Censos (INDEC); 2003 [cited 2007 Nov 15]. Available from: http://www.indec.mecon.ar/

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27 Aviles G, Paz M V, Rangeon G, Ranaivoarisoa M Y, Verzeri N, Roginski S, et al. Laboratory Surveillance of Dengue in Argentina, 1995-2001. Emerg Infect Dis. 2003 Jun; 9(6):738-42. 28 Ministerio de la Salud de la Nación. Sistema Nacional de Vigilancia Epidemiologia. In: Manuel de Normas y Procedimientos del Sistema Naciónal de Vigilancia Epidemiológica (SINAVE). Argentina; 1999. p.14-15. 29 Ministerio de la Salud de la Nación. Enfermedades Vectoriales. In: Manuel de Normas y Procedimientos del Sistema Naciónal de Vigilancia Epidemiológica (SINAVE). Argentina; 1999. p. 90-92. 30 who.int [homepage on the internet]. Geneva: World Health Organization, DengueNet 2007. Available from: http://www.who.int/csr/disease/dengue/denguenet/en/index.html 31 Ministerio de Salud. Presidencia de la Nación. Dirección de Epidemiologia de Nación. Brote de dengue en Paraguay-Riesgo en localidades fronterizas. Direpi\Alerta.1. 2007 Jan 15. 32 Red de Laboratorios. Casos Sospechos de Dengue –Interrogantes y Respuestas. In: Guia Practica de Laboratoria. Argentina; Mendoza: 2000. 33 Ministerio de Salud. Presidencia de la Nacion. Dirección de Epidemiologia de Nación. Casos de dengue hemorrágico en Paraguay. Riesgo en localidades fronterizas con antecedentes de brotes previos. Direpi\Alerta.2. 2007 Jan 23. 34 Heymann DL, editor. El control de las enfermedades transmisibles. 18th ed. Washington: Organización Panamericana de la Salud; 2005. 35 Mollar MCM, Falconi H. Control Dengue. Departamento de Epidemiologia, Division Zoonosis. Ministerio de Salud/Provincia de Mendoza. 36 Shekhar KC, Huat OL. Epidemiology of dengue/dengue hemorrhagic fever in Malaysia-a retrospective epidemiological study 1973-1987. Part I: Dengue hemorrhagic fever (DHF). Asia Pac J Public Health. 1992-1993;6(2):15-25. 37 Hussin N, Jaafar J, Naing NN, Mat HA, Muhamad AH, Mamat MN. A review of dengue fever incidence in Khota Bharu, Kelantan, Malaysia during the years 1998-2003. Southeast Asian J Trop Med Public Health. 2005 Sep;36(5):1179-86. 38 Reiskind MH, Baisley KJ, Calampa C, Sharp TW, Watts DM, Wilson ML. Epidemiological and ecological characteristics of past dengue virus infection in Santa Clara, Peru. Tropical Medicine and International Health. 2001 Mar;6(3):212-18. 39 Shekhar KC, Huat OL. Epidemiology of dengue/dengue hemorrhagic fever in Malaysia-a retrospective epidemiological study 1973-1987. Part II: Dengue fever (DF). Asia Pac J Public Health. 1992-1993;6(3):126-33.