It’s Fall Vaccination Time!

As the cold weather moves in, it’s time to think about fall vaccines to protect your horses. Below is a list of our recommended vaccinations and a brief summary of the diseases they help to prevent. Please contact us with any questions!

West Nile Virus

West Nile Virus (WNV) is cause by a virus that lives in a bird-mosquito life cycle. Signs of disease include fever and neurologic abnormalities such as trembling, head-pressing, circling, instability, abnormal gait, visual difficulty, and inability to swallow. There is no treatment for this disease aside from supportive care and this disease can be fatal. While humans can be infected with this disease, there is no direct horse- human transmission.

EWE (Eastern and Western Equine Encephalitis)

Eastern Equine Encephalitis (EEE) and Western Equine Encephalitis (WEE) are caused by viruses that lives in a bird- mosquito life cycle (and occasionally rodents). Transmission to horses usually occurs by mosquito bites. Signs of infection are neurologic abnormalities such as stumbling, head-pressing, loss of balance, circling, depression, and abnormal gait. Infected horses typically have a fever and abnormal bloodwork (low white blood cell count). EEE has a high potential to be deadly in unvaccinated horses. There is no treatment for these diseases aside from supportive care. Available vaccines for both diseases have been proven to be very effective for disease prevention. Both of these viruses can affect humans, causing similar signs as seen in horses, however transmission from horse to human has not been proven.

Potomac Horse Fever

Potomac Horse Fever (PHF) is caused by a bacterial organism (Neorickettsia risticii). This bacteria lives inside a fluke which resides within aquatic insects during the immature stages and within snails during the adult stages. The primary mode of infection in horses is likely by accidental ingestion of infected insects or snails that contaminate grass, hay or feed. PHF most commonly causes acute-onset fever, colic, anorexia, diarrhea, and/or laminitis. Horses that are vaccinated for Potomac Horse Fever may still show signs, but are usually less severely affected and have a better response to treatment, resulting in more favorable prognosis for survival. Treatment for PHF is with an intravenous antibiotic (oxytetracycline) and is usually most successful when started early in the course of infection.


Equine influenza virus (the flu) is also called by a virus (orthomyxovirus). The virus is easily aerosolized by respiratory secretions and is transmitted by direct contact or inhalation. It is highly contagious in unvaccinated individuals and causes destruction of the cells lining the respiratory tract, which can take up to 3-4 weeks to fully repair. Clinical signs can include nasal discharge, cough, increased respiratory rate, lethargy, poor appetite, exercise intolerance, and fever. There is no specific treatment other than supportive care and rest. The virus affects all ages of horses, although clinical signs are often more mild in older horses. It has a short incubation time of only a few days, and can cause an isolated case or an outbreak of an entire barn. The immunity following vaccination is short-lived, consequently it is important to vaccinate every 6 months or sooner in high risk situations.


Equine herpesvirus (also known as rhino, EHV or rhinopneumonitis) is caused by a virus (equine herpesvirus-1 or equine herpesvirus-4). Signs of respiratory infection vary based on type and strain of virus, but may include fever, lethargy, anorexia, nasal discharge and cough. Vaccination is indicated to reduce severity of illness and help prevent the spread of respiratory tract disease, particularly show horses or racehorses that travel. EHV-1 can also cause abortions and neurologic signs, so pregnant mares and horses exposed to pregnant mares should be vaccinated. Unfortunately, currently available vaccines have not been shown to provide reliable protection against the neurologic form of the disease. Some protection is, however, likely to be provided by appropriate vaccination. There is no specific treatment for these diseases and locations where horses are identified with the neurologic form of EHV-1 must undergo strict quarantine measures.

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