We don’t want to alarm you—but if you’re new to horse ownership, you should know that horses can catch a wide range of infectious diseases. Some just cause mild respiratory signs, while others are truly life-threatening. The good news? With a little knowledge, smart preventive strategies, and guidance from a veterinarian, you can manage or prevent most of these illnesses. Here’s a quick guide to equine infectious diseases that could make your horse sick and how they spread.
| Disease | Clinical Signs | How it Spreads | Contagious Between Horses? |
| Anthrax | Fever, muscle tremors, labored breathing, colic, bloody diarrhea, followed by sudden death | Bacteria in the soil or environment | No |
| Botulism | Drooling, poor tail, tongue and eyelid tone, muscle weakness and trembling, flaccid paralysis, difficulty swallowing, inability to stand | Bacteria or toxins in the soil or environment | No |
| Contagious Equine Metritis | In mares, vaginal discharge, infertility, abortion | Breeding/semen; contaminated equipment | Yes |
| Coronavirus | Fever, lack of appetite, depression, lying down frequently, diarrhea, colic | Feces | Yes |
| Equine Encephalomyelitis (EEE, WEE, VEE) | Fever, lack of appetite, lethargy, depression, neurologic signs | Biting insects such as mosquitoes | No |
| Equine Herpesvirus/ Rhinopneumonitis | Fever, nasal discharge, lethargy, neurologic disease, abortion | Nasal or oral secretions; abortion byproducts | Yes |
| Equine Infectious Anemia | Fever, anemia, muscle weakness, atrophy, depression, spots on mucous membranes | Biting insects; contaminated equipment | Yes |
| Equine Influenza | Fever, cough, nasal discharge, enlarged lymph nodes | Nasal or oral secretions | Yes |
| Equine Protozoal Myeloenchepalitis (EPM) | Ataxia, weakness, muscle atrophy, cranial nerve deficits, reduced sensation | Opossum feces | No |
| Equine Viral Arteritis | Fever, depression, edema, anorexia, conjunctivitis, hives, abortion | Breeding/semen; nasal or oral secretions; across the placenta | Yes |
| Leptospirosis | Fever, loss of appetite, uveitis, abortion, kidney or liver failure | Bacteria in the soil or environment; bodily fluids | Yes |
| Lyme Disease | Swollen joints, uveitis, neurologic signs | Ticks | No |
| Piroplasmosis | Weakness, lethargy, lack of appetite, fever, labored breathing, jaundice, colic, swollen abdomen | Ticks; contaminated equipment | No |
| Potomac Horse Fever | Fever, diarrhea, anorexia, depression, laminitis, colic, edema, abortion | Aquatic insects | No |
| Rabies | Fever, loss of appetite, difficulty swallowing, blindness, skin hypersensitivity, muscle twitching, loss of body control, incontinence, death | Saliva; bites from infected animals | Yes |
| Rhodococcus equi | Fever, lethargy, loss of appetite, rapid and/or difficulty breathing | Bacteria in the soil or environment | No |
| Rotavirus | In foals, diarrhea, colic, loss of appetite | Feces | Yes |
| Salmonellosis | Diarrhea, fever, lethargy, anorexia, colic, sepsis | Feces; contaminated equipment | Yes |
| Strangles | Fever, nasal discharge, abscesses in the lymph nodes below the jaw, difficulty swallowing, coughing | Nasal or oral secretions; contaminated equipment | Yes |
| Tetanus | Difficulty moving, lockjaw, agitation, sawhorse stance, extended neck, difficulty swallowing | Bacteria in the soil or environment | No |
| Vesicular Stomatitis | Ulcerative lesions on the lips, muzzle, nostrils and tongue, difficulty eating, salivation | Biting insects; contaminated equipment | Yes |
| West Nile Virus | Fever, lack of appetite, depression, lethargy, neurologic signs | Biting insects such as mosquitoes | No |
While equine infectious diseases can affect any horse, these are the most vulnerable:
- Immunocompromised horses, such as those with immunocompromising conditions like metabolic disease or horses under stress from travel, illness, or strenuous exercise.
- Unvaccinated horses.
- Young, unprotected foals.
Horses that travel frequently and co-mingle with other horses are more likely to get sick.
Related Reading:
- Safe and Sound: A Guide to Biosecurity for Horses
- How to Handle a Disease Outbreak on a Horse Farm
- Equine Vaccinations: What Your Horse Needs and When
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