Infectious Diseases of Animals
Core concepts
Understand the epidemiologic triad (host, agent, environment) and transmission routes (direct, indirect, vector-borne, vertical, airborne). Know reservoirs vs vectors vs fomites, and the difference between infection and disease. Study zoonotic agents (rabies, brucellosis, leptospirosis, Q fever, anthrax, tuberculosis) and transboundary diseases (FMD, ASF, CSF, rinderpest history, HPAI).
For each major disease, know the causative agent (bacterial, viral, prion, parasitic), species affected, key clinical signs, diagnostic test of choice, and control strategy (vaccination, test-and-slaughter, quarantine, vector control). Understand antigenic variation (e.g., influenza reassortment), latency (herpesviruses), carrier states, and vertical transmission. Know reportable/notifiable disease categories and the concept of foreign animal disease recognition.
Traps
- Confusing FMD (vesicular, cloven-hoofed) with vesicular stomatitis (also vesicular but zoonotic and New World).
- Assuming vaccination always prevents infection rather than reducing disease/transmission.
- Mixing prion diseases (scrapie, BSE, CWD) with viral encephalitides.
- Forgetting carrier animals in control programs (e.g., Salmonella carriers).
Worked rule of thumb
For any disease-control question, identify the interruption point: reduce susceptible hosts (vaccination), reduce contact (biosecurity, quarantine), or remove infectious sources (test-and-slaughter, culling). Then ask whether the agent has an environmental or wildlife reservoir-if so, eradication is far harder than control.
Example: FMD control uses rapid detection, movement restrictions, culling of infected/premises, and vaccination rings; the virus has no significant wildlife reservoir in most settings, making eradication feasible.