Rainstorms’ Aftermath — Water, Water Everywhere Raises Risk Of Livestock Disease, Human Mosquito Bites

AUSTIN Rushing water, stagnant ponds, or even the dry stages after wet periods can lead to outbreaks of livestock disease. Mosquitoes and biting flies, capable of carrying and transmitting diseases, thrive in the damp weather, and naturally-occurring anthrax can take a toll on livestock and wildlife when pastures dry after prolonged wet periods.

Horse owners should take precautions against mosquito-transmitted diseases by having their animals vaccinated against West Nile Virus (WNV) and the reportable diseases Eastern and Western Equine Encephalitis (EEE and WEE). “If you wait until cases of ‘sleeping sickness ‘occur in your area, you may have waited too long to vaccinate,” said Dr. Bob Hillman, Texas’ state veterinarian and head of the Texas Animal Health Commission (TAHC), the state’s livestock and poultry health regulatory agency.

“You need time for the vaccine to do its job, which is to build the animal’s immunity to a particular disease,” he said. “Vaccine can provide the best disease protection possible, but it’s also crucial to keep up with booster shots, as recommended by the vaccine manufacturer or your private veterinary practitioner. In 2006, 111 horses were confirmed to have West Nile Virus in Texas. So far this year, the disease has been confirmed in one horse, located in Willacy County.”

Three cases of Potomac Horse Fever, which is not a regulatory disease, have been confirmed in Kerr County by the Texas Veterinary Medical Diagnostic Laboratory. Potomac Horse Fever, first detected in Maryland in l979, is not typically found in Texas. Clinical cases usually are found near rivers, streams, ponds or canals. The infection involves tiny flukes that are parasites of water snails. The flukes hatch their offspring into the water, and these are then picked up by aquatic insects that molt into flying insects, including caddis flies and mayflies. Horses can become exposed to Potomac Horse Fever when they eat or drink anything contaminated with the insects.

Kerr County equine veterinarians are urging all owners to call their practitioner if equine animals exhibit signs of Potomac Horse Fever, which can include a reluctance to eat, fever, diarrhea, colic or inflammation around the hoof. Treatment includes antibiotics and supportive care.

Biting flies can mechanically transmit equine infectious anemia (EIA), sometimes called “swamp fever.” This incurable disease, for which no approved vaccine exists in the U.S., is a regulatory disease. TAHC regulations require horses and other equine animals to have a negative test for EIA within the previous 12 months before entering the state, or going to events, assemblies, trail rides, undergoing change of ownership or entering a breeding farm. The most commonly known test for EIA is the “Coggins” blood test. The incidence of EIA has dropped dramatically since l997, when 750 equine animals in Texas were found to be infected. Since January 2007, only 29 infected animals have been detected.

“EIA-infected horses can develop severe anemia, fever and swelling. In severe cases, EIA can kill the animals, but many times, the infected animal has few signs of disease,” noted Dr. Hillman. “Prevent EIA transmission by avoiding blood-to-blood contact between infected and ‘clean’ equine animals. Disinfect medical instruments and tack, and control flies. Biting flies carry blood from one animal to the next on their mouthparts, and they play a key role in the mechanical transmission of EIA.”

Infected equine must be maintained