An infectious disease is one that is spread between members of a species either by direct contact or a secondhand vector such as an insect or wild animal.

The 8 diseases listed below are potentially deadly, making prevention and early detection essential. Luckily, each has its own set of signs and symptoms as well as measures you can take to prevent infection.

1. West Nile

Infection with deadly West Nile disease is most common in the late summer or early fall in the northeast and Mid Atlantic regions when mosquitoes are rampant. The insects become vectors for the virus when they take a blood meal from an infected bird. They then transmit the disease when they move on to the next host.

Not all animals exposed to West Nile become ill, but horses seem to be especially susceptible. The virus affects the central nervous system causing encephalitis – inflammation of the brain.

Signs of West Nile:

loss of appetite
weakness or paralysis of hind limbs
impaired vision

head pressing
convulsions (seizures)
inability to swallow

walking in circles

An equine vaccination is available, but is not 100% effective against all strains of the disease. Reducing your horse’s risk of exposure to mosquitos is essential and can be done by reducing their breeding grounds. Mosquitos love stagnant water that collects in gutters, troughs, bird baths, recycling containers, old tires, wading pools, etc. Clean out and empty any water-collecting containers frequently. You may also opt to use an equine-safe insecticide spray.

2. Tetanus

Horses generally contract tetanus when an untreated wound becomes contaminated with the bacterium Clostridium tetanii which can be found in soil and manure. The bacteria are extremely hardy and can survive for long periods of time without oxygen. Tetanus proves deadly in 50-75% of cases.

Signs of Tetanus:

Muscular stiffness and spasms
Difficulty moving and eating

Tail often held straight out
Development of an anxious expression due to facial spasms
In advanced cases the horse will collapse with spasms, convulsions and death from respiratory failure

Vaccination against tetanus and good first aid practices are key to prevention. Prevent wounds by keeping barns and turn-out areas free from potential hazards.

3. Strangles (Streptococcus equi)

Strangles is highly infectious from horse to horse and caused by the bacterium Streptococcus equi equi. It causes abscessation of the lymphoid tissue of the upper respiratory tract and is transmitted by direct contact with infected horses, insects that have come in contact with contaminated nasal drainage, human contact from horse to horse and infected equipment or medical supplies.

In a small percentage of cases, ‘bastard’ strangles may occur when abscesses spread to other areas of the body. This is almost always fatal.

Signs of Strangles:

Fever (103°–106°F)
Nasal discharge
Difficulty swallowing

Respiratory noise
Extended head and neck

Swollen lymph nodes

Vaccination and quarantine of affected horses to prevent spreading the disease to other animals.

4. Equine Influenza (Flu)

Equine influenza is a highly contagious virus that is endemic in the US, meaning it circulates continuously in the equine population. Influenza can be spread through direct contact with an infected horse or contamination in the environment. The incubation period of 1-3 days allows the virus to spread rapidly throughout animals in close proximity before symptoms ever appear.

Signs of Equine Influenza

A harsh, dry cough of sudden onset that persists for 2-3 weeks or more
Clear nasal discharge progressing to thick, green-yellow discharge

Loss of appetite


While there are vaccinations available, it is difficult to provide full immunity against various strains of virus. New and traveling horses should be quarantined for at least 14 days as a safety precaution.


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