Anthrax Season Firing Up in Texas

With the weather in Texas transitioning rapidly from extreme rainfall to extreme heat, anthrax has reemerged in Tom Green county and caused the death of two horses so far.

Bacillus anthracis is a spore-forming bacteria that occurs worldwide. If an animal dies from the disease and the carcass isn't properly disposed of, the bacteria will lie dormant in the soil and resurface under specific weather conditions. The bacteria can also be transmitted via horseflies, explained Kenneth Waldrup, DVM, PhD, regional veterinarian with the Texas Department of State Health. These flies feed by cutting the skin and using a spongelike tongue to absorb pooled blood. If the fly moves on before ingesting a complete blood meal, it will repeat the process with another animal, thus transmitting bacteria on its mouthparts.

Tom Green county (the county containing the city of San Angelo) is in an area known to be endemic for Bacillus anthracis, Waldrup said. The fatal equine cases followed an outbreak among cattle and whitetail deer in another area of the county in July. Horseflies in this area are reported to be especially bad this year due to the earlier wet weather, Waldrup reported.

"Most livestock owners who have been there for any length of time routinely vaccinate their cattle," Waldrup said. "From what I understand on this particular case, these people had vaccinated their cattle but had not done the horses."

Anthrax cases have also been reported this summer in North Dakota, and an outbreak in Winnipeg has killed 50 animals, including two horses, according to published reports.

Affected horses might show clinical signs of fever, chills, severe colic, anorexia, depression, weakness, bloody diarrhea, and swellings of the neck, sternum, lower abdomen, and external genitalia, the Merck Veterinary Manual notes. Death usually occurs within two to three days of onset.

"This is a very fast disease," Waldrup said. "You see (affected animals), they're fine one morning, they're not fine in the afternoon, and they're dead the next morning."

An anthrax vaccine for livestock is available. It is a live vaccine, so it is important not to give it in conjunction with antibiotics.

"The vaccine is very good as far as prevention of the actual disease. The whole thing about the prevention is to truly prevent it—do it beforehand," Waldrup said. "In the case of anthrax, vaccination is a whole lot easier than trying to treat them. As long as the animal's alive, it's never too late (to vaccinate)."

Animals that die of anthrax require special handling and disposal to prevent further contaminating the area. Waldrup said it’s important to have a veterinarian collect a sterile swab for testing to confirm that anthrax is the culprit. These swabs can be submitted to the Texas Veterinary Medical Diagnostic Laboratories.

It is also important not to cut the animal open (or allow scavengers to do so), as the spores form when exposed to air, Waldrup said. The animal carcass should be incinerated or buried in place as soon as possible.

Waldrup also advised those with animals that succumb to anthrax to wear disposable gloves and a facemask when handling the carcass.

"It's not something to panic about, but just be careful," Waldrup said. "This is an infectious disease."

Anthrax is a reportable disease in Texas. Suspected cases should be reported to the Texas Animal Health Commission at 800/550-8242, where a veterinarian is on call 24 hours a day.

About the Author

Erin Ryder

Erin Ryder is a former news editor of The Horse: Your Guide To Equine Health Care. She owns a portly gray gelding named Duncan and dabbles in several equestrian disciplines, with an emphasis on dressage.

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