Water, water everywhere raises risk of livestock disease

Cattle Market & Farm Reports, Editorials
Dec 20, 2007
by WLJ

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 and the reportable diseases Eastern and Western Equine Encephalitis. “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 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 equines must be maintained at least 200 yards away from other equine animals, euthanized, or sent to slaughter.


“In the past, untested equine animals could be sold for slaughter through a livestock market. At the slaughter plant, blood samples were collected and sent for laboratory testing. Now that Texas equine slaughter plants have been closed, we can not ensure that horses moving to plants in other states or countries are tested. Therefore, we are requiring all horses to have a current EIA test, even when being sold for slaughter,” said Hillman.


Rain, followed by hot weather can coax the invisible bacteria Bacillus anthracis to the surface, a situation that has occurred on a ranch in Tom Green County where 17 head of cattle and a number of white-tailed deer have died. “Anthrax in Texas occurs nearly every year, and it is a reportable disease to the TAHC. If we know an outbreak is occurring, we can let ranchers in the area know that it’s time to vaccinate their livestock. There is no preventive treatment for wildlife,” said Hillman.


Anthrax naturally occurs worldwide and in many states of the U.S. Disease outbreaks have been reported in Minnesota, South Dakota and Canada this year. When an anthrax-infected animal dies and isn’t properly burned, the bacteria will infiltrate the soil and lie dormant (but not spread) for many years. Under ideal weather and soil conditions—a cool, wet spring, followed by a hot, dry spell—the bacteria will resurface on grass and forage. The disease cycle starts again when another animal ingests the resurfaced anthrax bacteria.


TAHC regulations require that an infected animal’s carcass, manure and bedding be incinerated. This prevents wild animals from being exposed to the disease, and it kills the bacteria, preventing another site where the anthrax bacteria can resurface. Hillman urged ranchers to wear gloves and long sleeves when preparing the burn site and to avoid moving the carcasses, if possible. Exposure to anthrax carcasses could cause a handler to develop a black skin lesion that requires prompt medical treatment.


“There is no need for vacationers or hunters to worry about naturally occurring anthrax. Just don’t touch or handle sick or dead animals, and don’t pick up bones or shed antlers. We usually advise hunters not to hunt feral or wild swine in the area during an anthrax outbreak. Feral swine may root around carcasses of anthrax-killed animals, becoming exposed to the bacteria but not contracting the disease.”


Hillman advised swimmers to avoid ponds or streams if dead animals are nearby. The same advice goes for pets, too. By the time hunting season starts, he said, cool weather usually puts an end to anthrax cases. “Always harvest only healthy-looking animals, and, as a routine practice, wear gloves when processing meat,” he said.


“In Texas, it is often ‘feast or famine,’ drought or flood,” said Hillman. “With each of the conditions, there are concerns about livestock health. So, while ranchers enjoy the lush grasses the rains have produced, they may have to control pests to lower disease risks. However, I don’t know many ranchers who would choose last year’s drought over some extra vigilance this year.”

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