Dr Ubaid N P
Community Medicine Dept
ACME, Pariyaram
Zoonoses
Definition - “those diseases and infections which
are naturally transmitted between vertebrate animals
and man”
a) Anthropo-zoonoses – infections transmitted to
man from lower vertebrate animals
b) Zoo-anthroponoses - infections transmitted
from man to lower vertebrate animals
c) Amphixenoses – infections maintained in both
man and lower vertebrate animals that may be
transmitted in either direction
Classification based on the type of
life cycle of the infecting organism
1.
Direct zoonoses: Transmitted from infected vertebrate host to a
susceptible host by direct contact, fomites or by a mechanical vector.
Undergoes little or no propogative or development changes during
transmission. Eg – Rabies, trichinosis, Brucellosis
2.
Cyclo zoonoses: Require more than one vertebrate host species to
complete the developmental cycle; no invertebrate host. Eg –
Echinococcosis, human taeniases
3.
Meta zoonoses: Transmitted biologically by invertebrate vectors;
multiplies or develops or do both in vectors. There is always an extrinsic
incubation period before transmission to another vertebrate host. Eg –
Arbovirus infection, Plague, Schistosomiasis
4.
Sapro zoonoses: Have both a vertebrate host & a non animal
developmental site or reservoir like, food, soil, plants. Eg – Larva
migrants, some mycoses
Yellow Fever
Introduction
• Zoonotic disease caused by an arbovirus
• Spectrum of disease varies from clinically indeterminate to severe cases
• Severe cases develop jaundice with hemorrhagic manifestations, albuminuria/
anuria, shock, stupor and coma
• Can have severe hepatic and renal involvement
• Death occurs between 5th and 10th day of illness
• Case fatality rate may reach 80% in severe cases
• 45 countries in Africa & Latin America has reported cases, with at risk population of
900 million
• No case has been reported in Asia, although the region is at risk as the conditions
required for transmission are present there
Epidemiological determinants
Agent factors
a) Agent
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Flavivirus fibricus; group B arbovirus; Togavirus family
b) Reservoir of infection
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In forest: monkeys & forest mosquitoes;
In urban areas: Man & Aede aegypti mosquitoes
c) Period of communicability
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Man: first 3 to4 days of illness;
Mosquitoes: After an extrinsic incubation period of 8 to 12
days, mosquitoes becomes infective for life
Host factors
a) Age & sex – All ages and sexes
b) Occupation – person who has contact with
forests (wood cutters, hunters)
c) Immunity – one attack gives life long
immunity; Infants born to immune mothers
have antibodies up to 6 months of life
Environmental factors
a) Climate – temp. of 24°C or over and relative
humidity of over 60% is required for
multiplication of virus and for the mosquitoes
to live long respectively
b) Social factors – Urbanization, dense
population, increases in number of people who
travel from endemic to receptive areas
Modes of transmission
Sylvatic(forest) YF - Intermediate YF -
Urban YF
Incubation period - 3 to 6 days
Treatment:
• No specific treatment
• Supportive care to treat dehydration and fever
• Antibiotics for secondary bacterial infections
Control of YF
• Jungle YF – continues to be uncontrollable
• Urban YF
1) Vaccination
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17D live attenuated
Sensitivity
Dose & Route of administration
Contra indications and ADRs
Vaccine interaction
2) Vector control
3) Surveillance
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Aedes aegypti index <1%
International measures
• Missing link of YF in receptive countries
• International Health Regulations(IHR) to
restrict the spread of YF
i. Travellers
ii. Mosquitoes
• International certificate of vaccination
• Reference centres
▫ National Institute of Virology, Pune
▫ Central Research Institute, Kasauli
Thank You