Venezuelan Equine Encephalitis Confirmed in Mexico

Due to recent confirmed cases of Venezuelan equine encephalitis (VEE) in horses in Southern Mexico, the Texas Animal Health Commission (TAHC) is encouraging area horse owners and veterinarians to be alert to any clinical signs of illness that could indicate an animal has contracted VEE.

Venezuelan equine encephalitis is a noncontagious, mosquito-borne viral infection of horses and other equids that can cause a severe and often fatal inflammation of the brain and spinal cord. Clinical signs of VEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (such as facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (including aggression, self mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs (such as headpressing, circling, blindness, and seizures).

Although the disease is typically only found in Central and South America, the recent equine fatality that resulted from a VEE infection in the Southern Mexican state of Tabasco has prompted the USDA to issue an import alert affecting horses in four Mexican states.

Effective immediately, and until further notice, horses and other equids originating from the states of Tamaulipas, Veracruz, Tabasco, and Chiapas or that have transited through these states are required to undergo an extended seven-day quarantine and observation for VEE in a vector-proof (double-screened) quarantine facility, rather than the standard three-day quarantine prior to entry into the United States. The import alert issued by USDA is a precautionary measure due to the one horse in Tabasco that has died from the virus.

The particular VEE strain being reported by Mexico is considered an endemic strain that doesn't normally cause disease in equids. A severe VEE outbreak that occurred in Texas in 1971 was caused by a different, more virulent strain of the virus. People also can be infected with VEE by mosquitos, but horse-to-horse and horse-to-human transmission is uncommon.

Considered a foreign animal disease, VEE is reportable to both the TAHC and the Department of State Health Services due to the potential for human illness.

"There have been no reported cases of VEE in recent years in Texas," said Andy Schwartz, DVM, TAHC state epidemiologist. "However, our close proximity to Mexico means that we will be keeping a close eye on any cases across the border and determining whether any further regulatory action will be needed. Vaccination and other protective measures for all equine including West Nile virus, Western and Eastern equine encephalitis (WEE/EEE) should be discussed with your veterinarian."

Additional Resources:

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More