7. Zoonoses Flashcards
What is the definition of a Zoonose?
Infections (Bacterial, Viral, Parasite or Fungal) that are naturally transmitted between Vertebrate Animals and Humans (The Source of the disease being from the Animal)
Note - of the 1415 pathogens currently known to affect humans, 61% are Zoonotic
What are examples of diseases which are transmitted from animals to humans, which are not Zoonoses?
- Malaria (from a Mosquito)
- Schistosomiasis (from a Snail) - Snail Fever
- Oncoceriasis (from a Fly) - River Blindness
- Elephantiasis (from a Fly / Mosquito) - Lymphatic Filariasis
Note - even though they are transmitted from the animal, they depend on the human host for part of their life-cycle
- What is an Anthroponosis?
- Give examples.
- “Reverse Zoonoses” - infections from humans which can effect animals
- a) Influenza (Virus affecting birds / pigs)
- b) “Strep Throat” (Bacteria affecting dogs)
- c) Leishmaniasis (Parasite affecting dogs)
- d) Chytridiomycosis (Fungus affecting amphibians)
What are the most common Bacterial Zoonoses?
- Salmonella (Common in the UK)
- Campylobacter (Common in the UK)
- Coxiella Burnetti (Q Fever) (Common in the UK)
- Chalmydophila Psittaci (Psittacosis / Ornitosis)
(Common in the UK) - Anthrax (Rare in the UK)
- Brucella (Rare in the UK)
- Leptospirosis
What are the most common Viral Zoonoses?
- Rabies (Emerging but Rare in the UK)
- Avian Influenza (Emerging)
- Ebola Virus Disease
- Yellow Fever
What are the most common Fungal Zoonoses?
- Dermatophytoses (Ringworm) (Common in the UK)
- Sporotrichosis
What are the most common Parasite Zoonoses?
- Toxoplasmosis (Common in the UK)
- Cysticercosis
- Echinococcosis
- Trichinellosis
- Visceral Larva Migrans (Toxocara)
How is Rabies transmitted?
From the bite of an infected animal, normally a dog (97%) or a bat
How does Rabies present?
The Rabies Virus travels to the Brain via the Peripheral Nerves (it can take up to 2 months) and so presents as an acute Encephalitis:
1. Malaise, Headache and Fever
2. Progression to Mania, Lethargy and Coma
3. Over-production of Saliva and Tears
4. Unable to swallow and Hydrophobia
5. Death by Respiratory Failure
How is Rabies diagnosed?
Diagnosis is difficult:
1. PCR of Saliva or CSF
2. Often confirmed post-mortem on brain biopsy
How is Rabies treated?
Immediately after the bite give post-exposure prophylaxis: Human Rabies Immunoglobulin infiltrated around the bite (if possible) + 4 doses of Rabies Vaccine over the next 14 days
Note - this is fatal if untreated
Where was Brucellosis an occupational hazzard?
- Farmers
- Vets
- Slaughterhouse Workers
How are humans infected with Brucellosis?
- During milking infected animals
- During parturition
- Handling carcasses of infected animals
- Consumption of unpasteurized dairy products
Note - the organisms are excreted in milk, placenta, and aborted foetus
How does Brucellosis present?
- Actue (1-3 weeks):
- a) Fever + Drenching Sweats
- b) Weakness, Headaches
- c) Splenomegaly
- Subacute (>1 month): Fever and Joint pains
- Chronic (>months or years): Flu-like symptoms
- Subclinical (commonest): 50% exposed have positive serology
What is the treatment of Brucellosis?
- Long acting Doxycycline for 2-3 months
- Rifampicin
- Intramuscular Gentamycin for 1st weeks
- Cotrimoxazole for 2 weeks (in CNS disease)
What is the commonest form of Leptospirosis?
L. Hardjo (cattle) - 11% of dairy workers have a positive serology, though most have no history of the illness
How does Leptospirosis present?
- Jaundice
- Liver Failure
- Renal Failure
What is the treatment of Leptospirosis?
- Usually benign
- Penicillin as early as possible
What is the main source of Toxoplasmosis?
Toxoplasma Gondii is found commonly in cats
How is Toxoplasmosis transmitted into humans?
- From oocysts in cat faeces
- From trophozoites in under-cooked meats
How does Toxoplasmosis infection present?
- Asymptomatic
- Acute: Pneumonia, Fever, Cough, Rash
- Chronic: Lymphadenopathy, Lymphcytosis, Atypical Mononuclear Cells on the Blood Film
- Chorio-Retinitis and Uveitis
- Congenital form: Hydrocephalus, Microphthalmos, Microcephaly, Convulsions, Calcification in Brain on X-Ray - usually fatal
How is Toxoplasmosis diagnosed?
Serology:
1. Toxoplasma Dye Test
2. IgM antibodies
How is Toxoplasmosis treated?
- Most don’t require treatment
- Sulphonamide and Pyrimethamine
- Tetracycline (occasionally)
What is the cause of Lyme Disease?
- Borrelia Burgdorferi
- Spirochaete found in wild Deer
How is Lyme Disease transmitted to humans?
Via Ticks
What can Lyme Disease go on to form?
- Acrodermatitis Chronica Atroficans (ACA)
- Lymphocytoma
- Neuroborreliosis (NB)
What is Acrodermatitis Chronica Atroficans (ACA)?
Note - this is caused by Lyme Disease
The Extensor Surfaces of the Distal Extremities (commonly of elderly) turn bluish red - and progress to atrophic disease
Peripheral Neuropathy common
What is Lymphocytoma?
Note - this is caused by Lyme Disease
Bluish, solitary, painless nodule found in the earlobe or Aerola
Note - more common in children
What is Neuroborreliosis (NB)?
Note - this is caused by Lyme Disease
Triad of:
1. Cranial Nerve Palsy (Normally Facial Nerve)
2. Radicular Pain (Migratory, worse at night)
3. Lymphocytic Meningitis
How is Lyme Disease diagnosed?
Clinically:
1. Single / multiple lesions - red area which can then spread (Erythema Migrans)
2. ACA and Lymphocytoma
3. Arthritis - very high serology titres from Synovial Fluid
