Veterinary Microbiology, Pathology and Parasitology
Veterinary microbiology, pathology and parasitology tests causal agents, lesion recognition and laboratory diagnosis. Expect questions that link a specimen to a stain, culture or parasite egg.
Core rules
- Gram stain: Gram-positive purple, Gram-negative pink. Anthrax is a Gram-positive, spore-forming rod with a capsule; do not open a suspect carcass.
- Brucella is a Gram-negative coccobacillus, zoonotic; diagnosis by serology and culture. Tuberculosis is acid-fast; Ziehl–Neelsen stain.
- Viruses need living cells; FMD and rabies are not treated with antibiotics. Rabies diagnosis is by brain tissue, not blood.
- Parasites: Fasciola hepatica uses a snail intermediate host; Haemonchus contortus lives in the abomasum and sucks blood; coccidia damage intestine; Babesia is tick-transmitted and causes haemoglobinuria.
- Pathology: inflammation, necrosis, hyperplasia and neoplasia are distinguished by cell pattern and tissue reaction; post-mortem sampling should include affected and marginal tissue.
Worked example
A sheep is pale, weak and has soft faeces; faecal flotation shows strongyle-type eggs. Reasoning: anaemia plus strongyle eggs points to Haemonchus, a blood-sucking abomasal worm. A faecal egg count does not measure worm burden directly in all cases, but anaemia and eggs together justify targeted anthelmintic treatment and pasture management. Coccidiosis would more typically cause diarrhoea in young lambs with oocysts, not marked anaemia.
Traps
Do not diagnose anthrax by opening the carcass. Do not confuse Gram stain colours. Do not call all diarrhoea in calves bacterial. Do not ignore zoonotic risk when handling Brucella or rabies suspects.