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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.html8/3/2019 Week 5 Zoonoses
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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
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