Since widespread flooding has occurred on the Prairies this year, livestock producers and horse owners living near areas where anthrax cases were previously reported may be considering vaccinations as a preventive measure.
But before horse owners make a decision about vaccinating, Dr. Chris Clark of the Western College of Veterinary Medicine (WCVM) recommends that they talk to their veterinarians first.
“Horses are relatively resistant to anthrax, and they’re even more unlikely to get exposed to the bacteria because of the way most owners keep their horses in smaller pastures or paddocks. Consequently the risk is typically very low,” explains Clark, a specialist in large animal medicine who has been involved in previous anthrax investigations in the United Kingdom and in Western Canada.
“Only people who live in high risk areas and manage horses like cattle and other livestock are at a high risk for anthrax.”
Anthrax is a reportable disease in Canada that’s caused by the bacteria Bacillus anthracis whose spores can survive in soil for decades. Cattle, horses, bison or deer can ingest anthrax when they graze in areas where flooding or digging has brought the bacterial spores to the surface.
Once ingested, the spores germinate and grow in an animal’s intestinal tract — releasing potent toxins that cause the animal to die if left untreated. Clinical signs of anthrax include bloody discharge from the animal’s nose, mouth, anus or vagina, abdominal swelling and a carcass that decomposes very quickly. The mortality rate in the early stages of an anthrax outbreak is nearly 100 per cent.
According to veterinarians at the Canadian Food Inspection Agency (CFIA), anthrax is different from other reportable diseases. It’s considered to be an environmental disease since its spores are in the soil and they’re available in a wide, geographic region.
Although anthrax is a non-contagious disease, the bacterial spores can “spread” to other areas through scavengers, migrating birds or flies. Excessive moisture and flooding can also wash anthrax spores from one area to another.
The only anthrax vaccine that’s licensed in North America is manufactured by the Colorado Serum Company (www.colorado-serum.com). The vaccine is available for cattle, horses, mules, sheep, goats and pigs, while off-label use can be considered for bison and farmed elk and deer. The live culture anthrax spore vaccine, which was introduced in the 1950s, is highly effective and considered to be safe with minimal risk to animals and to humans.
However, Clark points out that the anthrax vaccine typically causes significant reaction (such as local swelling) at the injection site — an issue that can be particularly upsetting for horse owners. As well, the vaccine company and the WCVM advise owners of miniature horses and young foals to use other alternatives for preventing the disease.
Once animals receive the vaccine, it takes from seven to eight days for them to build up enough immunity against the disease. In circumstances where an animal is already exposed to anthrax, Clark says that it’s better to treat with antibiotics such as oxytetracycline or penicillin, then vaccinate the animal later. “What’s important to remember is that you can not give the vaccine and treat with antibiotics at the same time.”
Visit the Canadian Food Inspection Agency (www.inspection.gc.ca) for more information.
Reprinted with permission from Horse Health Lines, publication for the Western College of Veterinary Medicine’s Equine Health Research Fund. Visit www.ehrf.usask.ca to sign up for our e-newsletter.