Dr Ubaid N P Community Medicine Dept ACME, Pariyaram.

Dr Ubaid N PCommunity Medicine DeptACME, 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 determinantsAgent factors

a) Agent ▫ Flavivirus fibricus; group B arbovirus; Togavirus

family

b) Reservoir of infection ▫ In forest: monkeys & forest mosquitoes; ▫ In urban areas: Man & Aede aegypti mosquitoes

c) Period of communicability▫ 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 transmissionSylvatic(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 YF1) Vaccination

▫ 17D live attenuated▫ Sensitivity▫ Dose & Route of administration▫ Contra indications and ADRs▫ Vaccine interaction

2) Vector control3) Surveillance

▫ Aedes aegypti index <1%

International measures

•Missing link of YF in receptive countries•International Health Regulations(IHR) to

restrict the spread of YFi. Travellersii. Mosquitoes

•International certificate of vaccination•Reference centres

▫National Institute of Virology, Pune▫Central Research Institute, Kasauli

Thank You