With the recent rain and flooding across the state of Texas, mosquito activity is expected to increase. So, Texas Animal Health Commission (TAHC) officials are encouraging horse owners to consult with their private veterinary practitioner regarding vaccinating their equids against mosquito-borne illnesses such as Eastern equine encephalitis (EEE), Western equine encephalitis (WEE), Venezuelan equine encephalitis (VEE), and West Nile virus.

The commission noted that EEE, WEE, and VEE are reportable diseases to the TAHC.

A mosquito-borne viral disease of all equid species, EEE can cause horses to suddenly die or show progressive central nervous system disorders. Signs of disease can include unsteadiness, erratic behavior, and a marked loss of coordination.

A viral disease that mainly affects horses, WEE is primarily transmitted by mosquitoes. Similar to EEE, WEE is characterized by central nervous system dysfunction.

A viral disease that affects horses and causes illness in humans, VEE has not been confirmed in the United States for many years; however, a recent VEE outbreak occurred in Mexico. Mosquitoes most often transmit the disease after the insects have acquired the virus from birds and rodents. Humans also are susceptible when bitten by an infected mosquito, but direct horse-to-horse or horse-to-human transmission is very rare. Signs of disease in horses vary widely, but all result from the degeneration of the brain. Early signs include fever, depression, and appetite loss.

About 20 to 50% of horses infected with WEE die, and the death rate is 75-100% of animals infected with EEE. The mortality rate for VEE is 40 to 80%.