A few moments with your local veterinary practitioner can help protect horses, mules and donkeys against mosquito-borne diseases, advises Dr. Terry Conger, veterinarian and state epidemiologist for the Texas Animal Health Commission (TAHC), the state's livestock health regulatory agency. Vaccines are available to protect horses against three viral diseases that pose a risk to Texas horses: West Nile Virus (WNV), and Eastern and Western Equine Encephalitis (EEE) and (WEE). The three diseases are forms of "sleeping sickness," that can cause infected horses to develop debilitating fever, swelling of the brain, muscle tremors, weakness and extreme fatigue, and in about a third or more of cases, death of the animal.

"As of June 24, 26 cases of West Nile Virus (WNV) have been reported this year by the Texas Department of Health's (TDH) Zoonosis Control Division, which maintains the state's statistical database for reporting laboratory-confirmed WNV cases in humans, mosquitoes, birds, and horses," said Dr. Conger. "According to the TDH, the 26 cases have been confirmed in one horse each in Angelina, Calhoun and Van Zandt Counties. WNV also has been detected in six birds and four mosquito pools in Harris County; one bird in Orange County; one bird and two mosquito pools in Dallas County; four mosquito pools in Tarrant County, three mosquito pools in Jefferson and two in Nueces Counties."

"In June 2002, Texas had its first case of WNV, and by year's end, 1,699 equine cases had been reported. Denton County was hit hardest, with 69 equine cases," explained Dr. Terry Conger, TAHC's state epidemiologist. "More unreported cases undoubtedly occurred across the state, as owners may have been reluctant to ask their veterinarian or the TAHC for assistance. Only laboratory-confirmed cases are included in the state's database. Most private veterinary practitioners send blood or tissue samples for WNV testing to the Texas Veterinary Medical Diagnostic Laboratory (TVMDL) in College Station or Amarillo."

WNV infection was first detected in the U.S. in New York in l999, and since then, the virus has swept across the country, spread by infected mosquitoes that have fed on birds carrying the disease. Only four states on the U.S. mainland have not reported cases: Arizona, Nevada, Oregon and Utah. Dr. Conger said it is likely that these states also will eventually have cases of WNV.

"Sporadic outbreaks of WEE and EEE also occur throughout the U.S., and this year we may have cases in Texas, as South Carolina, Florida and Georgia have already confirmed EEE in horses. Because Texas has a large mosquito population and history of infection in past years, it is prudent to have equine animals vaccinated against WEE and EEE every year," said Dr. Conger. "It is important to note that the vaccines for WNV, WEE and EEE do not provide cross-protection. For example, WNV vaccine protects only against WNV." As of late June, 14 horses in South Carolina have been diagnosed with EEE. In Florida, more than 110 EEE cases in equine animals have been confirmed, and in Georgia, a dog, three birds and 16 horses have tested positive for the disease.

"WNV, EEE and WEE are going to be with us always, as these diseases have become endemic in our country. Even if you try to reduce the mosquito population in your area, vaccinating against these mosquito-borne diseases still needs to be part of routine horse health maintenance," said Dr. Conger.

Dr. Conger explained that the WNV vaccine for horses vaccination requires a series of two shots, administered three to six weeks apart. After the second injection, several more weeks must pass before full immunity is developed. Equine animals vaccinated last year should receive a single WNV booster this year. In areas where mosquitoes are a continual problem year-round, animals should receive a WNV booster every six months. "Owners should take action now to get their equine animals vaccinated, before cases become more widespread," urged Dr. Conger.

"EEE and WEE vaccines are available in a combined product. To develop disease protection, the animal will need two injections, 30 days apart. A booster shot is then needed annually or biannually," said Dr. Conger. "In most cases, horses can be vaccinated for WNV, EEE/WEE at the same time." He said some veterinarians also employ the EEE/WEE vaccine in an off-label use to protect ratites (emus, rheas and ostriches) against the disease.

"While no vaccine can guarantee 100 percent protection, it's much better than no protection," commented Dr. Conger. "Last year, Colorado State University followed more than 500 equine animals infected with the WNV in Colorado and Nebraska. The death rate was greater than 36 percent in animals that had not received vaccine. The death loss dropped to around 20 percent for animals that had received at least one dose of WNV vaccine. Of the 13 animals properly vaccinated with two doses of vaccine, a dozen survived."

Dr. Conger said equine animals infected with WNV, EEE or WEE, may exhibit similar signs, including fever, irregular gait, teeth grinding, drowsiness, an inability to swallow. Affected animals may be paralyzed and be unable to rise. He said TAHC and public health officials advise owners to have sick animals tested to diagnose the disease that caused illness or death, because rabies always must be considered when an animal is disoriented or staggers. If an owner has been exposed to rabies while caring for a sick horse, appropriate preventive health measures must be taken immediately, he said.

"WNV, EEE and WEE impact a community's animals, and owners should take advantage of opportunities to protect their stock by reducing mosquito populations and vaccinating," said Dr. Conger. "Although these "sleeping sicknesses" aren't regulatory diseases, veterinarians are required to report cases, so that disease trends or outbreaks can be followed and all preventive and educational measures can be taken."