Lecture 1.3 - Zoonoses PDF

What is a zoonosis?: ◦A ‘zoonosis’ is any disease or infection that is naturally transmissible from vertebrate animals to humans’ - World Health Organisation ◦Major cause of emerging human disease ◦Wide ranging causative agents - bacterial, viral, fungal, protozoan, prion (variant Creu...

What is a zoonosis?: ◦A ‘zoonosis’ is any disease or infection that is naturally transmissible from vertebrate animals to humans’ - World Health Organisation ◦Major cause of emerging human disease ◦Wide ranging causative agents - bacterial, viral, fungal, protozoan, prion (variant Creutzfeldt-Jakob disease) ◦Host specificity ‣ Macaque Herpes Virus (Cercopithecine herpesvirus 1) - high mortality rate in humans without anti-viral treatment ‣ HIV Why is zoonotic disease important?: ◦General practice vs hospital medicine ◦Pets in the home ◦Occupational hazards ◦Wildlife ◦Hobbyists ◦Young, elderly and immunosuppressed patients ◦Pregnancy Routes of transmission: ◦Direct contact - dermatophytosis (ringworm), Orf (Parapoxvirus), Sarcoptic Mange (Sarcoptes scabiei) ◦Scratches/bites - cat scratch fever (Bartonella henselae, Rabies (Lyssavirus) ◦Inhalation - Psittacosis (Chlamydophila psittaci) ◦Ingestion - vCJD, Tuberculosis (M.bovis), Campylobacter, Salmonella ◦Faeco-oral - Toxoplasmosis (Toxoplasma gondii) Influenza A viruses: ◦Most influenza viruses originate from birds ◦Aquatic birds are the main natural reservoir for influenza A viruses ◦Great zoonotic potential as can infect various avian and mammal hosts and transmit to humans ◦High potential for genome change by: ‣ Point mutations - sporadic mutations to the genome (antigenic drift) - no proofreading function on RNA ‣ Reassortment - of viral segments of Influenza A viruses during Co-infection (antigenic shift) ◦Rate of point mutations is higher in humans than in avian hosts ◦Reassortment -> concern for new respiratory pandemics ◦Various flu outbreaks in history ◦Subtype according to two surface proteins: ‣ Haemagglutinin (H)- binds virus particle to cell to initiate infectious cycle ‣ Neuraminidase (N) - allows release of viral particles to complete infectious cycle ◦High pathogenicity vs Low pathogenicity Avian influenza ‣ Used in chicken species Tuberculosis: ◦Caused by Mycobacteria that are part of the Mycobacteria tuberculosis complex ◦Zoonotic tuberculosis caused by Mycobacterium bovis ◦Economically very important disease of cattle that is also spread by badgers  ◦Primary route of transmission - ingestion ◦Occupational risk of airborne transmission ◦Challenges: ‣ Differentiation for M.tuberculosis clinically and in the laboratory ‣ Misdiagnosis ‣ Treatment - resistance to Pyrazinamide (drug) Salmonellosis: ◦Salmonellosis is generally considered a food borne illness - eggs (Salmonella enteritidis) ◦Less commonly known risk from pet reptiles ◦Salmonella enteritidis outbreaks associated ◦Risk from skin, faeces and feed animals ◦Education is very important ◦At risk groups - very young children particularly Pets in the home: ◦The most common source of zoonotic disease in the UK: ‣ Dermatophytoses ‣ Toxoplasmosis ‣ Cat scratch fever ‣ Psittacosis ‣ Protozoa infections ‣ Rabies Dermatophytoses: ◦‘Ringworm’ - fungal not parasitic ◦Risk species - dogs, cats, guinea pigs, rabbits ◦Can be non-pruritic in animals ◦Difficult to identify in long coats ◦Commonly transferred to children, the elderly and immunosuppressed patients Toxoplasmosis: ◦Infection with Toxoplasma gondii ◦Risk from cat faeces and infected meat ◦Can cause miscarriage, still birth and birth defects ◦Eduction of pregnant patients ‣ Cat litter trays - pregnant women should avoid changing litter trays ‣ Gardening - wear gloves ‣ Fruit and veg - wash before use Cat scratch fever: ◦Bacterial infection with Bartonella henselae ◦Can occur through any bite or scratch that breaks the skin ◦Cats under 1 year old more likely to carry  ◦Asymptomatic in cats ◦Symptoms can include: ‣ Round, raised purulent lesions at site of injury ‣ Fever ‣ Enlarged local lymph nodes ‣ Headache ‣ Can cause severe systemic complications Psittacosis: ◦Bacterial infection with Chlamydophila psittaci ◦Carried by all species of bird - parrots and pigeons highest risk ◦Transmission - primarily inhalation ◦Incubation 1-4 weeks ◦Symptoms - flu-like symptoms to severe pneumonia ◦At risk groups - occupational exposure, immunosuppressed and young/elderly individuals, pregnant women ◦Pet birds - education is needed Protozoa infections: ◦Examples include Giardia, Cryptosporidium and Coccidia ◦Giardia: ‣ Common in young dogs, especially from poor breeding backgrounds Occupational hazards: ◦People working with farm animals: ‣ Orf (viral skin infection contracted from sheep and goats) ‣ Ringworm ‣ Toxoplasmosis - pregnant sheep and lambs ◦People working in zoos with exotic animals: ‣ Bacterial infections - especially working with primates ‣ Protozoal infections