Equine owners advised to act against EEE

Texas A&M AgriLife veterinarian recommends vaccinations to protect horses from mosquito-borne disease

by Adam Russell

A Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, expert advises horse owners to take proactive steps to protect their horses after cases of eastern equine encephalitis, EEE, infections in two Houston County horses were confirmed. These are the first reported cases of the mosquito-borne illness in Texas, according to the Texas Animal Health Commission, TAHC.

As a protective measure, equine owners are encouraged to consider vaccinating their horses against mosquito-borne illnesses such as eastern equine encephalitis, western equine encephalitis, WEE, Venezuelan equine encephalitis, VEE, and West Nile Virus, WNV.

Mosquitoes most often transmit eastern equine encephalitis, western equine encephalitis and Venezuelan equine encephalitis after the insects have acquired the virus from birds and/or rodents. Humans are also susceptible to these viruses when bitten by an infected mosquito, but direct horse-to-horse or horse-to-human transmission is very rare. EEE is rare in humans, with an average of 11 cases reported each year, according to the Centers for Disease Control and Prevention.

Terry Hensley, DVM, TVMDL assistant agency director and Texas A&M AgriLife Extension Service veterinarian, Bryan-College Station, said horse owners should take precautions to protect their animals against infection.

“WNV and EEE are the two mosquito-borne diseases we see the most in horses,” he said. “Equine owners should familiarize themselves with diseases as they are a potential threat each year from spring through early fall.”

Signs of infection to look for in horses

Infection causes nonspecific clinical signs and often affects the central nervous system. Affected equines should be given supportive care based on the severity of their symptoms.

Clinical signs may include:

• Moderate to high fever of 102.5-104.5 degrees.
• Severe depression, known as “sleeping sickness.”
• Behavior changes.
• Impaired vision.
• Circling or head pressing.
• Muscle twitches.
• Inability to swallow.
• Paralysis.
• Convulsions.
• Death.

Equine owners or producers who suspect eastern equine encephalitis, western equine encephalitis, or Venezuelan equine encephalitis, should contact their private veterinarian for evaluation. All confirmed diagnoses or suspected cases must be reported to the Texas Animal Health Commission at 1-800-550-8242.

Prevention for mosquito-borne diseases is paramount

The eastern equine encephalitis, western equine encephalitis and Venezuelan equine encephalitis vaccinations, repeated at least annually, effectively prevent clinical disease. Private veterinarians should be consulted if horses are in or traveling to higher-risk areas, including near the border of Mexico. Higher-risk areas have year-round mosquito populations or have previously reported cases.

Owners and producers should reduce mosquito attractants, such as standing water. Place fans where the horses rest and limit their outdoor activities at dawn and dusk. Owners can also use equine-approved mosquito repellent to deter bites. Mosquito dunks approved for water troughs can be used to prevent mosquito larvae development.

“Aside from practicing mosquito control around your barn, stable and home environment, the primary method of reducing risk in horses for these mosquito-borne viruses is vaccination,” Hensley said. “The vaccines available for both diseases have proven to be very effective.”

According to Hensley, most documented cases of West Nile virus and eastern equine encephalitis come from nonvaccinated or undervaccinated horses. TVMDL experts encourage horse owners to work with their veterinarians to establish a vaccination program, especially in areas with a historical presence of both viruses.

General disease information and how to protect horses from these mosquito-borne diseases of equine species can be found on the TAHC website.