EPIDEMOLOGY AND CONTROL OF HELMINTH PARASITES

EPIDEMIOLOGY AND CONTROL OF HELMINTH PARASITES SUBMITTED BY:

TATHAGATO ROY

What is EPIDEMIOLOGY?It is the study of distribution of diseases in a particular community or district.Study and analysis of patterns, causes and effects of health and disease state in particular population.The data are best obtained either directly in a field or from a source such as hospitals or regional health clinic records

Classification:Epidemiology of parasites are mainly divided into 2 types:Protozoan Epidemiology and Helminthic Epidemiology

HELMINTHSWhat are Helminths?Helminths (Greek meaning worms)Helminths are mostly parasitic worms ; but some are free living.

CLASSIFICATION OF HELMINTHSTwo major phyla of helminths:NEMATHELMINTHES (Roundworms): Includes major intestinal worms like soil-transmitted helminths Ascaris, and the filarial worms that cause lymphatic filariasis.PLATYHELMINTHES (Flatworms): Includes two classesTREMATODA (Flukes) Leaf like; e.g., Schistosomes and Fasciola CESTODA (Tapeworms) Ribbon like; e.g., Pork tapeworm that causes Cysticercosis.

HELMINTH INFECTIONSRoundworm infection(Nematodiasis):

Filariasis (Wuchereria bancrofti, Brugia malayi infection)Onchocerciasis (Onchocerca volvulus infection)Also known River blindness or Robles disease.Soil-transmitted nematode disease:It includes ascariasis (Ascaris lumricoides infection).It is an intestinal roundworm.

Tapeworm Infection (Cestodiasis):

Echinococcosis (Echinococcus infection): Infection through ingestion of parasitic egg with contaminated food, water or soil.Hymenolepiasis (Hymenolepis infection): Caused by the introuction of tapeworm species; Hymenolepis nana or Hymenolepis diminuta.Taeniasis/ Cysticercosis (Taenia infection): Acquired by humans through ingestion of tapeworm larval cysts (cysticerci) in undercooked pork or beef.

Trematode infection (Trematodiasis):Schistosomiasis/Bilharziasis (Schistosoma Infection): Caused by parasitic worm that live in certain types of freshwater snails.Amphistomiasis (Amphistoma infection): It can be transmitted via penetration of skin or by direct ingestion through contaminated food or water.Fascioliasis (Fasciola infection) It is a water and food borne zoonotic disease Caused by two parasites: F. Hepatica and F. Gigantica.

PREVALENCE OF HELMINTHISISRoundworm infected diseases:FILARIASIS: Caused by Wuchereria bancrofti, Brugia malayi GLOBAL SCENERIO:An estimated 120 million people in tropical and subtropical areas of the world are infected with lympathic filariasis; of these, 25 million men have genital disease (most commonly hydrocoele) and almost 15 million; mostly women, have lymphoedema or elephantiasis of the leg.

A recent study suggests that during the past 13 years >96.71 million cases were prevented or cured with MDA (Methylenedioxyamphetamine) treatment, yet, as many as 36 million cases of hydrocoele and lymphoedema remain.Of the total population requiring preventive chemotherapy, 57% live in South-East Asia region(9 countries), 37% live in African region (35 countries).One of the leading causes of global disability LF (Lympathic Filariasis) accounts for 2.8 million DALYs (Disability Adjacent Life Year).

INDIAN SCENERIO:

A district-level endemicity map created in India in the year 2000, shows that of the 289 districts as many as 257 were found to be endemic.About 553 million people are exposed to risk of infection; and of them about 146 million live in urban and the remaining in rural areas.About 31 millions are estimated to be carriers and over 23 million suffer from filarial disease menifestations in India.B. Malayi is prevalent in the states of Kerela, Tamil Nadu, Andhra Pradesh, Madhya pradesh, Orissa, Assam, West Bengal.

Bihar has highest endemicity (over 17%) followed by kerela(15.7%) and Uttar Pradesh(14.6%).Andhra Pradesh and Tamil Nadu Has About 10% endemicity.Goa showed the lowest endemicity (>1%), followed by Lakshwadeep (1.8%), Madhya Pradesh(above 3%) and Assam (5%).

ONCHOCERCIASIS (River Blindness): Caused by Onchocera volvulus Symptoms include itching, bumps under skin, blindness.GLOBAL SCENERIO: About 37 million people are infected with this parasite, about 300,000 of those have been permanently blinded.According to 2002 WHO report, Onchocerciasis has not caused a single death, but its global burden is 987,000 Disability Adjusted Life Years (DALYs).

As of 2008, about 99% of Onchocerciasis cases occurred in Africa, and it is currently endemic in 30 African countries, Yemen and isolated regions of South America.Infection reduces the host immunity and resistance to other diseases, which results in an estimated reduction in life expectancy of 13 years.This disease is not prevalent in India.

ASCARIASIS:

Most common helminthic human infection worldwide, causative agent Ascaris lumbricoides.

GLOBAL SCENERIO: Highest prevalence in tropical and sub-tropical regions where warm wet climates provide environmental conditions that favour year-round transmission of infection and areas with inadequate sanitations where suboptimal sanitation practices lead to increased contamination of soil and water.

In United States ascariasis is the third most frequent helminth infection exceeded only by hookworm and Trichuris trichura (whipworm).1.4 billion of the population i.e 25% are infected with A. lumbricoides.Ascariasis is found mostly in Asia(73%), Africa (12%), South America (8%).

INDIAN SCENERIO: High prevalence rates are found in Tamil Nadu(85%) and Kashmir (70%).

The following table shows the prevalence of roundworm infection as reported by some workers from different parts of India:

PREVALENCE OF TAPEWORM INFECTION (CESTODIASIS):Prevalence of Echinococcosis (Echinococcus Infection:GLOBAL SCENERIO:Greatest infection is found in the temperate zones including several parts of Eurasia (the Mediterranean regions, Southern and Central parts of Russia, central Asia and China), Australia, some parts of America and Northeast Africa.

Worldwide distribution of the zoonotic strains of Echinococcus granulosus and geographical endemicity.

INDIAN SCENERIO:The disease is endemic in India.High prevalence is reported from Kashmir, Andhra Pradesh, Tamil Nadu and Central India.

Prevalence of Hymenolepiasis (Hymenolepis infection):GLOBAL SCENERIO:The prevalence of H. nana in remote communities in Northwest Australia is remarkably high, 55%.In Bat Dambang, Cambodia middle school students were found to have a 2.4% prevalence.In 2006, a study in rural mexico found that 25% of the children ages 6-10 in 12 schools were infected with H. nana.Zimbabwe children in both small town and high-density suburbs suffer from H. nana.

Studies reported an overall prevalence rate of 24%in urban areas and 18% prevalence in rural towns.

Prevalence of Taeniasis/Cysticercosis (Taenia infection) GLOBAL SCENERIO:More than 80% of the worlds 50 million people who are affected by epilepsy live in low- and lower-middle-income countries.T. solium is the cause of 30% of epilepsy cases in many endemic areas where people and roaming pigs livein close proximity.

Figure: Endemicity of cysticercosis around the world

INDIAN SCENERIO:Cysticercosis is prevalent in virtually in all states of India, except in Kerela and Jammu and Kashmir.NCC(Neural Cysticercosis) accounts for anywhere between 8.7 to 50% of patients presenting with recent onset of seizure.The peculiarity of the disease in India is the high incidence of patients with the solitary form of the disease, namely, Solitary Cysticercus Granuloma (SCG).Pig rearing communities of the northern state of Uttar Pradesh reported that 38% of the members of that community has evidence of taeniasis.

The prevalence of Taeniasis is probably in Northern than in Southern areas.PREVALENCE OF TREMATODE INFECTION (TREMATODIASIS):SCHISTOSOMIASIS/ BILHARZIASIS:It is considered second only to malaria as the most devastating parasitic disease in the tropical countries.In Sub-Saharan Africa, more than 2000 deaths per year are due to schistosomiasis.

Figure: Prevalence of schistosomiasis showing the non endemic and endemic areas in world

Schistosoma mansoni: Distributed throughout Africa.Transmission also occurs in the Nile river valley in Sudan and Egypt, South America: including Brazil, Suriname, Venezuela Caribbean(low risk): Dominican Replublic, Guadeloupe, Martinique and Saint Lucia.Schistosoma Haematobium:Distributed throughout Africa: Southern and Sub-Saharan Africa including the great lakes and rivers as well as smaller bodies of water.Transmission also occurs in the Mahgreb region of North Africa.

Schistosoms japonicum:Found in Indonesia and parts of China and South-East Asia.Schistosoms mekongi:Found in Cambodia and Laos.Schistosoma Intercalatum:Found in parts of central and West Africa.FASCIOLIASIS (Fasciola infection):Human Fasciolasis has been reported from countries in Europe, America, Asia, Africa and OceniaThe incidence of human cases has been increasing in 51 countries of the 5 continents.

In Europe, human fasciolosis occurs mainly in France, Spain and Portugal.In Mexico, 53 cases have been reported.In Central America, the Caribbean Island, especially in zones of Puerto Rico and CubaIn South America; Bolivia, Equador and Peru are highly infected

INTENSITY OF SOME MAJOR HELMINTHIASES:SCHISTOSOMIASIS:S. haematobium infection intensity reduces with ageChildren are more highly affected and infected than adultsLow infection probability for males than in femalesThe incidence is usually more among those people who constantly get in contact with the schistosome infected waters through activities such as farming, fishing, swimming and washing.Death rate is very low or negligible.

FILARIASIS:Repeated mosquito bites over several months to years are needed to cause Lympathic Filariasis.This disease cause a negligible death rate but it can cause permanent disabilitiesIt affects both males and femalesASCARIASIS:It infects all ages of human. But mostly children of 2-10 year of age and intensity decreases over 15 years of age.Most prevalent in areas of low socioeconomic status and thus poverty and malnutritionIt exerts a chronic effect on host nutrition.

TAENIASIS/CYSTERCOSIS:Most often in rural areas of developing countries, where pigs roam freely and eat human faeces and where hygiene practices are poorWorldwide as of 2010 it caused about 1,200 deaths, up from 700 in 1990.The mean age at death was 40.5 years (range 288)The 33 US-born persons who died of cysticercosis represented 15% of all cysticercosis-related deaths. The cysticercosis mortality rate was highest in California, which accounted for 60% of all cysticercosis deaths

ECHINOCOCCOSIS:Cystic echinococcosis is rarely fatal. Occasionally, deaths occur because of anaphylactic shock or cardiac tamponade in heart .Hydatid disease is seen in subjects of any age and sex, although it is more common in those aged 2040 yrs It is a disease of rural areas where farming is practiced traditionally.

SCHISTOSOMIASIS:The manifestations of schistosomal infection vary over time as the cercariae, and later adult worms and their eggs migrate through the body.DermatitisItchy papular rash1-3cm big round bumpsThe rash can occur between the first few hours and a week after exposure and lasts for several days.CLINICAL SYMPTOMS, MORPHOLOGICAL AND PHYSICAL ALTERATIONS

A similar, more severe reaction called "swimmer's itch" reaction can also be caused by cercariae from animal trematodes that often infect birds.Katayama fever:Acute schistosomiasis (Katayama fever) may occur weeks or months after the initial infection as a systemic reaction against migrating schistosomulae as they pass through the bloodstream through the lungs to the liver.

Symptoms include:Dry cough with changes on chest x-rayFeverFatigueMuscle achesMalaiseAbdominal painEnlargement of both the liver and the spleen

The symptoms usually get better on their own but a small proportion of people have persistent weight loss, diarrhea, diffuse abdominal pain and rash.

Chronic Disease:In long established disease adult worms lay eggs that can cause inflammatory reactionsThe long term manifestations are dependent on the species of schistosome as the adult worms of different species migrate to different areas. Many infections are mildly symptomatic, with anemia and malnutrition being common in endemic areas.Genitourinary disease:The worms of S. haematobium migrate to the veins around the bladder and ureters

This can lead to blood in the urine 10 to 12 weeks after infection.Over time, fibrosis can lead to obstruction of the urinaryBladder cancer diagnosis and mortality are generally elevated in affected areas, and have efforts to control schistosomiasis in Egypt have led to decreases in the bladder cancer rate. tract, hydronephrosis and kidney failure.The risk of bladder cancer appears to be especially high in male smokers, perhaps due to chronic irritation of the bladder lining allowing it to be exposed to carcinogens from smokinIn women, genitourinary disease can also include genital lesions that may lead to increased rates of HIV transmissiong

Gastrointestinal Disease:The worms of S. mansoni and S. japonicum migrate to the veins of the gastrointestinal tract and liver.Eggs in the gut wall can lead to pain, blood in the stool, and diarrhea (especially in children).Severe disease can lead to narrowing of the colon or rectumEggs also migrate to the liver leading to fibrosis in 4 to 8 percent of people with chronic infection, mainly those with long term heavy infection.

Central Nervous system diseaseCentral nervous system lesions occur occasionally.Cerebral granulomatous disease may be caused by S.japonicum eggs in the brain. Communities in China affected by S. japonicum have been found to have rates of seizures eight times higher than baseline.Similarly, granulomatous lesions from S. mansoni and S. haematobium eggs in the spinal cord can lead to transverse myelitis with flaccid paraplegia.

FILARIASIS:Elephantiasis affects mainly the lower extremities, while the ears, mucous membranes, and amputation stumps are affected less frequentlyWuchereria bancrofti can affect the legs, arms, vulva, breasts, and scrotum (causing hydrocele formation), while Brugia timori rarely affects the genitals.Those who develop the chronic stages of elephantiasis are usually amicrofilaraemic, and often have adverse immunological reactions to the microfilariae, as well as the adult worms.

The list of signs and symptoms mentioned in various sources for Lymphatic Filariasis includes the 31 symptoms listed below: (major)Swollen lymph nodes ,Lymphedema ,Swollen armpit lymph nodes ,Swollen groin lymph nodes ,Arm swelling ,Breast swelling ,Leg swelling ,Male genital swelling ,Elephantiasis ,Lymphangitis ,Fever ,Aches ,Pain ,Epididymitis ,Orchitis ,Eosinophilia ,Hydrocele ,Chyluria , Thickened skin

ASCARIASIS:Most people who are infected with only a small number of worms have no symptoms. Clinical features depend on the affected body siteMigrating larva:As larval stages travel through the body, they may cause visceral damage, peritonitis and inflammation, enlargement of the liver or spleen, and an inflammation of the lungs. Pulmonary manifestations take place during larval migration and may present as Loeffler's syndrome, a transient respiratory illness associated with blood eosinophilia and pulmonary infiltrates with radiographic shadowing

Intestinal blockage:The worms can occasionally cause intestinal blockage when large numbers get tangled into a bolus or they may migrate from the small intestine, which may require surgery. More than 796 A. lumbricoides worms weighing up to 550g [19 ounces] were recovered at autopsy from a 2-year-old South African girl. The worms had caused torsion and gangrene of the ileum, which was interpreted as the cause of death

Bowel obstruction:Bowel obstruction may occur in up to 0.2 per 1000 per year.Sometimes the worm blocks the Ampulla of Vater or goes into the main pancreatic duct resulting in acute pancreatitis with raised serum levels of amylase and lipase.

Allergies:Ascariasis may result in allergies to shrimp and dustmites due to the shared antigen, tropomyosin; this has not been confirmed in the laboratory

Malnutrition:The worms in the intestine may cause malabsorption and anorexia which contribute to malnutrition.The malabsorption may be due to a loss of brush border enzymes, erosion and flattening of the villi, and inflammation of the lamina propria.Others:Ascaris have an aversion to some general anesthetics and may exit the body, sometimes through the mouth.

Taeniasis/cysticercosis:Taeniasis is generally asymptomatic.

It is not fatal, although cysticercosis can cause epilepsy and neurocysticercosis can be fatal.]Heavy infection is indicated by intestinal irritation, anaemia, and indigestion.

The eggs enter the intestine where they develop into larvae. The larvae enter bloodstream and invade host tissues. This clinical condition, called cysticercosis, is the most frequent and severe disease caused by any tapeworm.

It can lead to severe headaches, dizziness, occasional seizures, dementia, hypertension, lesions in the brain, blindness, tumor-like growths, and low eosinophil levels. It is the cause of major neurological problems, such as hydrocephalus, paraplegy, meningitis, convulsions, and even death.

It can cause antigen reaction that induce allergic reaction.It is an also rare cause of ileus, pancreatitis, cholecystitis, and cholangitis.

Echinococcosis: In the patients who are infected with E. granulosus and therefore have cystic echinococcosis, the disease develops into slow-growing mass in the body.

These slow-growing masses, are called cysts.these cyst are also common in patients that are infected with alveolar and polycystic echinococcosis. The cysts found in those with cystic echinococcosis are usually filled with a clear fluid called hydatid fluid, are spherical, and typically consist of one compartment and are usually only found in one area of the body

If the patient is symptomatic, the symptoms will depend largely on where the cysts are located. For instance, if the patient has cysts in the lungs and is symptomatic, they will have a cough, shortness of breath and/or pain in the chest.

On the other hand, if the patient has cysts in the liver and is symptomatic, they will suffer from abdominal pain, abnormal abdominal tenderness, hepatomegaly with an abdominal mass, jaundice, fever and/or anaphylactic reaction.

Some of the other symptoms includes: Bloody sputum, cough, severe skin itching.

PREVENTION AND TREATMENTSchistosomiasis:Prevention:Prevention is best accomplished by eliminating the water-dwelling snails that are the natural reservoir of the disease.Avoiding swimming or wading in freshwater when you are in countries in which schistosomiasis occurs. Swimming in the ocean and in chlorinated swimming pools is safe.Drinking safe water. Although schistosomiasis is not transmitted by swallowing contaminated water, if your mouth or lips come in contact with water containing the parasites, you could become infected. Water used for bathing should be brought to a rolling boil for 1 minute to kill any cercariae, and then cooled before bathing to avoid scalding. Water held in a storage tank for at least 1 - 2 days should be safe for bathing.

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Treatment:Schistosomiasis is treatable by taking by mouth a single dose of the drug praziquantel annually. Other possible treatments include a combination of praziquantel with metrifonate, artesunate, or mefloquineAnother agent, mefloquine, which has previously been used to treat and prevent malaria, was recognised in 20082009 to be effective against schistosoma

Filariasis:Prevention:Avoidance of mosquito bites through personal protection measures or community-level vector control is the best option to prevent lymphatic filariasis. Periodic examination of blood for infection and initiation of recommended treatment are also likely to prevent clinical manifestations.To eliminate lymphatic filariasis (LF) as a public health problem we must stop the spread of infection. Levels of worm larvae (microfilaria) in the blood of infected persons must be reduced so that mosquitoes cannot transmit the worms from one human to another.

Treatmennt: The strategy for interrupting transmission is an annual single co-administration of two drugs for at least five years. The two alternative regimens are: single doses of albendazole (400mg) plus Mectizan (150-200 mg/kg/body wt) or single doses of albendazole (400mg) plus DEC (6mg/kg/body wt). DEC, developed over 50 years ago, is an inexpensive and effective anti-filarial drug which is used to treat LF in many countries. DEC is available in tablet form and in a fortified salt formulation for daily intake at meal times. Mectizan (generic name: ivermectin) is an oral anti-parasitic drug, discovered and developed by Merck & Co. Inc. which is effective against both LF and onchocerciasis. Mectizan is provided free of charge by Merck & Co. Inc. for the treatment of onchocerciasis in all endemic countries and for LF in African countries where onchocerciasis and LF co-exist. Albendazole, donated by GlaxoSmithKline for LF prevention, is a well-established anti-parasitic treatment, given to an estimated 500-800 million people, mostly children, for intestinal infections over the past 20 years.

Ascariasis:Prevention:The best way to prevent ascariasis is to always:Avoid ingesting soil that may be contaminated with human feces, including where human fecal matter ("night soil") or wastewater is used to fertilize crops.Washing hands with soap and warm water before handling food.Wash, peel, or cook all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with manure. By-Not defecating outdoors,effective sewage disposal systemsIn areas where more than 20% of the population is affected treating everyone is recommended. This has a cost of about 2 to 3 cents per person per treatment. This is known as mass drug administration and is often carried out among school-age children.

Treatment:Albendazole 400 mg one dose orally is the drug of choice. Ascariasis commonly coexists with whipworm infection, which appears to be more susceptible to albendazole than to mebendazole. Albendazole is not recommended during pregnancy; pyrantel pamoate is the drug of choice in these cases.Alternative therapy is mebendazole (100 mg bid for 3 d or 500 mg as a single dose). Mebendazole is not recommended during pregnancy; pyrantel pamoate is the drug of choice in these cases.Paralyzing vermifuges (eg, pyrantel pamoate, piperazine, ivermectin) should be avoided in patients with complete or partial intestinal obstruction since the paralyzed worms may necessitate or further complicate surgery.Vitamin A supplementation improved growth development of children in Zaire; de worming did not improve growth development in this study.Drug therapy affects only adult worms. If the patient lives in an endemic area or has recently relocated, he or she may still be carrying larvae that are not yet susceptible. Such patients should be re-evaluated in 3 months and retreated if stool ova persist. In endemic areas, reinfection rates approach 80% within 6 months.Nitazoxanide, a drug used primarily for protozoal infection, was shown to have 89% clinical efficacy for the treatment of ascariasis in rural Mexico and may offer a future alternative to other medications

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