Introduction to Animal Diseases
Key concepts, classifications, causes, transmission, prevention, and basic management
1. What Is an Animal Disease?
- Definition – Any deviation from normal health in animals caused by internal or external factors that impairs physiological functions.
- Importance – Affects animal welfare, agricultural productivity, public health (zoonoses), and biodiversity.
2. Major Classifications
| Category |
Description |
Typical Examples |
| Infectious (Communicable) |
Caused by pathogens that can spread between animals (and sometimes to humans). |
Foot‑and‑mouth disease, avian influenza, rabies, bovine tuberculosis |
| Non‑Infectious (Non‑communicable) |
Result from genetics, nutrition, management, or environmental factors. |
Nutritional deficiencies, metabolic disorders, congenital anomalies |
| Zoonotic |
Infectious diseases that can be transmitted from animals to humans. |
Brucellosis, anthrax, leptospirosis, salmonellosis |
| Emerging & Re‑emerging |
Newly identified or previously controlled diseases that reappear. |
African swine fever, Nipah virus, COVID‑19 (suspected animal origin) |
3. Common Causative Agents
| Agent Type |
Characteristics |
Representative Diseases |
| Bacteria |
Prokaryotic, often treatable with antibiotics. |
Pasteurellosis, anthrax, leptospirosis |
| Viruses |
Obligate intracellular parasites; vaccines are primary control. |
Rabies, foot‑and‑mouth disease, avian influenza |
| Fungi |
Opportunistic; thrive in moist, warm environments. |
Ringworm, aspergillosis |
| Parasites |
Include protozoa, helminths, ectoparasites. |
Coccidiosis, liver fluke, mange |
| Prions |
Misfolded proteins, no nucleic acids; extremely resistant. |
Scrapie, chronic wasting disease |
| Toxins |
Produced by plants, microbes, or environmental contaminants. |
Mycotoxicosis, botulism, heavy‑metal poisoning |
4. Routes of Transmission
| Route |
Mechanism |
Examples |
| Direct Contact |
Physical interaction, bite, sexual contact. |
Rabies (bite), bovine viral diarrhea |
| Indirect Contact |
Shared feed, water, equipment, fomites. |
Salmonella via contaminated feed |
| Airborne/Aerosol |
Respiratory droplets or dust particles. |
Avian influenza, foot‑and‑mouth disease |
| Vector‑borne |
Insects, ticks, mites act as carriers. |
Lyme disease (ticks), bluetongue (midges) |
| Vertical |
Mother to offspring (in utero, birth, milk). |
Bovine viral diarrhea, toxoplasmosis |
| Environmental |
Soil, water, pasture contamination. |
Clostridial enterotoxemia, leptospirosis |
5. Clinical Signs – A Quick Reference
| System |
Common Signs |
Typical Diseases |
| Respiratory |
Cough, nasal discharge, dyspnea |
Pneumonia (bacterial, viral), pasteurellosis |
| Gastrointestinal |
Diarrhea, vomiting, weight loss |
Coccidiosis, salmonellosis |
| Neurological |
Ataxia, seizures, paralysis |
Rabies, listeriosis |
| **Derm |
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