Veterinary Microbiology and Immunology
Veterinary Microbiology and Immunology
This domain tests bacterial, viral, fungal, and parasitic structure and diagnosis, plus innate and adaptive immunity, vaccines, and serological tests.
Core rules
- Bacterial cell wall structure determines Gram staining; Gram-positive cells retain crystal violet, Gram-negative cells decolourise and take safranin.
- Culture needs correct medium, atmosphere, and temperature; colony morphology and biochemical tests support identification.
- Viruses replicate only in living cells; diagnosis uses PCR, antigen detection, serology, or isolation.
- Innate immunity is rapid and non-specific; adaptive immunity is specific, with humoral and cell-mediated arms.
- Vaccines: live attenuated, killed, toxoid, subunit; maternal antibody can block active immunisation in young animals.
Worked example
Cattle die suddenly; a blood smear shows square-ended Gram-positive rods with a capsule. Reasoning: large encapsulated rods in blood from a sudden bovine death suggest Bacillus anthracis. Do not open the carcass; confirm with staining and PCR. This is a zoonosis, so notify authorities and handle samples with protection.
Traps
- Calling anthrax a Gram-negative organism.
- Confusing clostridial toxins with anthrax septicaemia.
- Using serology to prove active infection without paired samples or vaccination history.
- Ignoring biosafety and zoonotic risk.
Exam focus
Match organism, stain, lesion, host, and diagnostic test. State whether a test detects antigen, antibody, or nucleic acid.