Texas has joined at least five other states this year in reporting cases of Eastern Equine Encephalitis (EEE) infection in horses. In Houston County, in the southeast corner of the state, a horse with clinical illness has tested positive for the disease, and in the north central Texas, in Denton County, a vaccinated horse also tested positive and exhibited clinical signs of disease. EEE, which can be transmitted to humans by infected mosquitoes, also has been reported this year in horses in Georgia, Florida, Maine, Tennessee, and New Hampshire­and in Ontario, Canada.

“Infected horses are a ‘sentinel’ or warning that infected mosquitoes are in the area, and measures should be taken to protect humans against exposure to the dangerous pests,” said Dr. Andy Schwartz, state epidemiologist for the Texas Animal Health Commission (TAHC), the state’s livestock and poultry health regulatory agency. “Protect yourself and your horses with a mosquito spray containing DEET, get rid of stagnant water, and avoid being outside at night, when mosquitoes are more active.”

“Horses with mosquito-borne encephalitic viruses, such as EEE, Western Equine Encephalitis (WEE) or West Nile Virus (WNV), may stagger, appear confused, and act erratically. Owners should contact their veterinarian immediately, if their equine animals exhibit clinical signs of these diseases. About half of infected animals may be saved, with the appropriate supportive care,” said Dr. Schwartz. Although EEE, WEE and WNV are not regulatory diseases, they are reportable to the TAHC and to the Texas Department of State Health Services, due to their potential to cause human disease.

“Vaccines are readily available to protect equine animals against mosquito-borne encephalitic diseases, but they must be given according to the manufacturer’s" directions, and it takes at least a week to 10 days after vaccination for protective antibodies to develop. Booster shots also must be given as needed. Heed your veterinarian’s advice,” he said. “As good as vaccines are at protecting against infection, there are rare times when a vaccinated animal will still contract disease. That is no reason to avoid vaccinating your animals.”

Dr. Schwartz noted that, in 2002, when West Nile Virus was first detected in Texas, 1,699 equine animals were stricken with infection. West Nile vaccine has helped cut those case numbers from 716 in 2003 to only two cases in 2008. “Vaccinating against mosquito-borne diseases has to be a part of routine equine health care,” he said. “Don’t stop, just because case numbers drop.”