week 5 zoonoses

8/3/2019 Week 5 Zoonoses

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ZOONOSESLearning objectives1.What are zoonoses and howare they transmitted?2.What major factors need to beconsidered in order to control andprevent zoonoses?3.Examples of zoonoses causedby bacteria, viruses and protozoa


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What are zoonoses?

-diseases that affect both animals andhumans

-animals are the reservoirs of thepathogens-

humans encounter the zoonotic

pathogen when they cross into theanimal cycle


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Zoonoses-transmission of the infectious agentto humans from an ongoing reservoir life cyclein animals, without the permanent establishmentof a new life cycle in humans.

A zoonosis is an animal disease transmissible to

humans, generally by direct contact, aerosols,or bites.

Diseases in animals may be enzootic, presentendemically in certain populations or epizootic,With incidence reaching epidemic proportions

Epizootic diseases occur on periodic, sometimes

cyclic basis.

Definitions


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Over 200 zoonoses have beendescribed and they have been known

for many centuries. They are caused by all types of

agents: bacteria, parasites, fungi,

viruses and unconventional agents.


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Modes of transmission 2 means transmission of pathogens

from animals to humans

1.direct: from animal to human: eg rabiesvirus is transmitted from a diseasedanimal to a person through a bite orcontact with the animals saliva

2. Indirect: Pathogen transmitted fromanimal to humans through vector


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Elements that Contribute to the

Emergence of a New Zoonoses

Microbial/viral (e.g. mutations and evolution)

Individual host (e.g. acquired immunity (vaccination)and lack of immune surveillance (AIDS)

Population host (e.g. transportation and urban crowding)

Environmental (e.g. ecological and climate influences)


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Reasons for emergence of

zoonoses alteration of the environment affecting the size and

distribution of certain animal species, vector andtransmitters of infectious agents of humans

increasing human population favouring an increase level ofcontact between human and infected animals

industrialization of foods of animal origin changes in foodprocessing and consumer nutritional habits

life style of people

Increasing movements of people as well as trade ofanimals and animals products and decreasing activities forthe surveillance and control for major zoonoses


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Increases in Zoonotic Pathogens

Global human and livestock populations continue to grow-this brings people and animals in closer contact

Advanced transportation makes long distance travelpossible in less than the incubation periodof most infectious agents

Massive ecological and environmental changes broughtabout by humans

Zoonotic agents may be the choice for manybioterrorist activities


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Zoonotic Microbial Pathogens

Pathogen Animal Diseas

BacteriaBacillus anthracis Cattle Anthrax

Borrelia burgdorferi Mice,deer tick Lyme disease

Camplylobacter Cattle , poulty

Listeria monocytogens

Salmonella spp Cattle, poultry Gastroenteritis

Yersinia pestisLeptospiraBrucella

Rodents, fleasrat

PlagueLeptospirosisBrucellosis

VIRUS

Dengue virus Monkeys, mosquitoes Dengue fever

HantavirusRabies

RodentsRaccoons, skunks bats,

foxes

PneumoniaRabies


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Other parasitic zoonoses aretrematodosis,

echinococcosis/hydatidosis,toxoplasmosis and trichinellosis


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Yersinia pestisand Plague Plague-an infection of rodents and small animals that may be

transmitted to humans -caused by bacterium, Yersinia pestis.= G negative, facultative

anaerobe, two forms of plague :bubonic plaque and pneumonic plaque clinical features: inflammation and swelling of lymph nodes

(buboes), especially in the groin area Fever, chills, headache, general malaise, chest, muscle pain, nausea When the disease is limited primarily to involvement of lymph nodes,

it is called bubonic plague

Plague that invades the lungs and is transmitted by the airborneroute through direct exposure to large respiratory droplets is calledpneumonic plague. Cells of Y.pestis either inhaled directly or via the

blood or lymphatic circulation. Symptoms usu. Absent until lst day ortwo of the disease bloody sputum Pneumonic plague-uncommon but it represents an especially serious

public health problem. Highly contagious and can spread rapidly viaperson-to person respiratory route.

Septicemic plaque is the rapid spread ofY.pestisthroughout body viathe bloodstream without the formation of buboes , usu cause death

before diagnosi can be made.


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Modes of transmission mostcases of human plague are bubonic form in

which Y. pestisis transmitted from animals to humans

through bites of infected fleas

fleas feeding on infected animals contract Y pestiswhich reproduces in the flea intestinal tract

when the infected fleas feed on another animal or a

person, they regurgitate Y pestisinto the bite wound The natural reservoir for Y. pestisis wild rodents Other wild animals: rabbits, coyotes, wolves domestic

cats, dogs-can harbour Y.pestis

plague that circulates within a wild animal populationthe natural cycle of plaguesylvatic plague


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humans accidentally contract Y.pestisfrom thesylvatic plague cycle when people move intoareas where sylvatic cycle is occurring or wheninfected animals or infected fleas move into areaswhere humans live.

Bubonic plague circulate among urban rodentssuch as rats . this cycle is known a urban plague The rats acquire Y.pestisfrom wild rodents and

then humans come into contact with infected ratfleas

Urban plagueis a much greater threat tohumans than slyvatic plague. Greater contactwith infected rat fleas in crowded cities


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REPORT

In 1981- a middle aged woman inCalifornia died of bubonic plague

Pet cat-killed an infected chipmunk.5 days later, cat died with difficultbreathing and bloody nasaldischarge. 3 days later, the womandeveloped fatal disease

Cat exhumed and an autopsy-revealed both the lungs and lymph

nodes were infected with Y.pestis


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Prevention

reduce risk of people being bitten by fleasinfected with Y. pestis

rat control program critical: periodicsurveillance and testing, proper garbageand refuse disposal

public should be alerted of possible riskarea. Eg campers, hunters

pneumonic plague; strict precautions mustbe taken to interrupt airborne transmission


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Discussion on local example:

Nipah virus outbreak in Malaysia

Leptospirosis in Malaysia

Etiologic agent

Epidemiology

Steps taken by public health authorities in

control of disease spread


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BACKGROUND

Nipah virus is a newly recognised zoonotic virus.

Nipah virus caused disease in animals and in humans

through contact with infectious animal.

First was discovered in 1999. Named after the location where it was first detected in

Malaysia.

Member of the virus family Paramyxoviridae.

This virus infect a wide range of host and produce disease causing

causing significant mortality in human.


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ECONOMIC IMPORTANCE OFTHE DISEASE

From September 1998 April 1999, there was large outbreak

of encephalitis caused by Nipah virus in Malaysia.

A total of 265 people were infected, and 105 died.

About 99% of cases had occupational exposure to pigs. 1.1 million of pigs were culled.

The outbreak in Perak result in the huge planning, logisticsand cost.

Various agencies were involved in to control the diseaseoutbreak such as DBI (Ipoh City Hall), JKR (Public WorksDept), RELA, Drainage and irrigation Dept, Agriculture Deptand etc.

Pig industry; a multi million dollar industry collapsed

Disallowed to export pig anymore


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AGENT OF THE DISEASE

The virus that cause this disease is the Nipah Virus.

The are believed that certain species of fruit batsare the natural host of the virus (Pteropid fruit batsincluding Pteropus vampyrus(Malayan flying fox)and Pteropus hypomelanus(Island flying fox).

These bats are susceptible to the infection with thisvirus but they do not get ill

Transmission of Nipah virus from flying foxes topigs is thought to be due to an increasing overlapbetween bat habitats and piggeries in peninsularMalaysia.


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MODE OF TRANSMISSION

Animal to animal

- scientist speculate that bats waste/ fruit

contaminated by bat saliva fell into pig pens andwere consumed by the pigs.

Animal to human

- require close contact with contaminated tissue orbody fluids from infected animals.

Human to human (has not beenreported)


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Laboratory trials suggest the following variations in

presentation of illness in pigs by different routes of

transmission.

Clinical Presentation of Nipah Virus by Route of Exposure

Route of

exposure

Characteristics

Oral

inoculation

Incubation period 14-16 days

Mild clinical signs and gross pathology

Parenteral

inoculation

Narrow study of two pigs revealed a more severe disease,

closer resembling natural exposure

Incubation period about 7-10 days

In-contact pigs Rapid infection

Neutralizing antibodies detected at day 14

Adapted from Nor 1999 (seeReferences).
http://www.cidrap.umn.edu/cidrap/content/biosecurity/ag-biosec/anim-disease/nipah.htmlhttp://www.cidrap.umn.edu/cidrap/content/biosecurity/ag-biosec/anim-disease/nipah.html


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THE RESERVOIRS

Natural reservoir-Certain sp of fruit bats (referred to as flying fox).

Animal Reservoirs

- Bats: serves as a carrier

- Pigs: source of infection among most humancases in Malaysia outbreak of Nipah (through

close contact). Other potential seropositive animals

- Dogs, rat, goats, horses and cats


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PREVENTION

Reduce transmission of Nipah virus to pigs by removingthe fruit source on a farm.

Import / export precaution and biosecurity should beincreased.

Increased hygiene and updated protocols on pigoperations are necessary.

National surveillance to detect any additional infectedherds.

Personal protection equipment (PPE) among people

exposed to pigs Studies of the virus should be managed in a high-level of

biosecurity laboratory (BSL-4) as respiratory secretionscontain the virus.


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Control of zoonoses: factors

to consider: multiple targets to consider: humans, animals and

vectors multiple targets can provide opportunities for

control from a single human target animals: a diversified threat: direct contact or

indirect contact ;urine, saliva, feces are infective animal reservoirs vectors: not only they transmit pathogens but also

act as reservoirs resistance factors control measures themselves may represent

problems: eg use of pesticides and antimicrobialagents may be harmful to humans


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The control of neglectedzoonotic diseases

At least 61% of all human pathogens are zoonotic,and have represented 75% of all emergingpathogens during the past decade.

Except for the newly emerging zoonoses such asSARS and highly pathogenic avian influenza H5N1,the vast majority are not prioritized by healthsystems at national and international levels and are

therefore labeled as neglected.


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Many zoonotic diseases impactsignificantly on human health as well

as livestock productivity, thusundermining livelihoods both bycausing illness in the household and

threatening its livestock and theiroutput.


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Prevention

increase surveillance

Adequate government inspection and control ofmeat, herd and milk production

control and elimination of animal reservoir

Food processing : pasteurization of milk

Proper cooking

Introduction of vaccine Strict quarantine

Notification of diseases

Sanitation control of farms

week 5 zoonoses

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