Important Fall Equine Vaccinations

Equine Fall Vaccination:
EEE, EHM, and Potomac Horse Fever Cases in Virginia


As we near the fall months, it’s time to get up to date on your horse’s vaccines. The Virginia Department of Agriculture has reported several positive cases of fatal diseases in Virginia this summer. Among the diseases reported are Eastern Equine Encephalitis (EEE), Equine Herpesvirus Myeloencephalopathy (EHM), and Potomac Horse Fever (PHF). All of these can be prevented or reduced in severity with proper vaccination, yet horses, in our area and across Virginia, are being diagnosed and dying from these diseases.


Equine Herpesvirus Myeloencephalopathy

Equine Herpesvirus Myeloencephalopathy is a neurological disease of horses caused by Equine Herpesvirus-1 (EHV-1). There are several different strains of the Equine Herpes Virus (EHV) these can cause respiratory problems, reproductive problems, neurologic problems and even death. EHV can be spread from horse to horse through contact with aborted fetuses, contact with nasal or oral discharges or by inhaling infected material in the air. Fortunately, EVH is not zoonotic, meaning it cannot be spread to humans. Some of the signs seen in horses can include being unsteady or weak on the rear limbs, not being able to urinate, and fever. The neurologic form of this disease is typically fatal.

Eastern Equine Encephalitis

Eastern Equine Encephalitis is another neurological disease caused by a virus. Normally, the virus lives in wild birds, but it is transmitted to mosquitoes and can then be spread to horses and humans. The virus cannot be transmitted directly from the horse to humans however. As was the case in Virginia, EEE often occurs near wetlands. However, EEE cases can occur wherever mosquitoes are present. Symptoms of EEE can include incoordination, stumbling, and weakness. These symptoms eventually progress to seizures and death. There is no effective treatment for EEE therefore infections usually result in death. The EEE vaccine is one of our core vaccine recommendations. It is most important to get this vaccine in the spring; however, a booster near then end of summer can help prevent disease should there be a fall mosquito epidemic.

Potomac Horse Fever

Potomac Horse Fever is caused by an intracellular bacterium called Neorickettsia risticii. The bacterium lives within flukes and is transmitted via water to snails and small flies. Horses pick up the bacteria by accidentally consuming the infected flies or snail larva. Signs of PHF are varying, but normally include a sudden fever. Other symptoms could also include lethargy, anorexia, colic-like signs, diarrhea, abortion, laminitis and death. Horses diagnosed with PHF can often be successfully treated with doxycycline and intensive fluid therapy. There is a vaccine available for PHF that may lessen the severity of the disease. We would recommend giving this vaccine to your horse. PHF dehydrates horses quickly, and it can be very hard to maintain their hydration. Oftentimes, successful treatment requires daily fluids and veterinary care for at least a few days. This vaccine is optional and may not be needed in your area. You, as the owner, should consult with your veterinarian about the benefits of this vaccine. If the vaccine is given, it is normally administered in the spring and boostered over the summer.


Equine Vaccine Recommendations:

Product Frequency of vaccine Vaccine Recommendations
Tetanus* Annually, booster if wound Core vaccine
EEE/WEE* Annually, 2x year in heavy mosquito areas Core vaccine
Rabies* Annually Core vaccine
West Nile Virus* Annually, 2x year in heavy mosquito areas Core vaccine
EHV-1/4 2x year Recommended if traveling frequently, also for breeding animals
Strangles 2x year Recommended if traveling frequently
Influenza 2x year Recommended if traveling frequently
PHF 2x year Consult your veterinarian

* Core vaccines are strongly suggested. These vaccines are safe and effective at preventing these potentially fatal diseases.
While spring is the most common time for equine vaccination, we are still within mosquito season, and it’s not too late to booster your horse. Additionally, if you have not had your horse vaccinated for Rabies or Tetanus this year, those core vaccines are very important. Please call to schedule a vaccination appointment soon!