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Vaccination key to anthrax prevention

posted by Horse Owner Today    |   April 20, 2011 20:10

     Since widespread flooding is predicted 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.

In 2006, an unusually wet spring followed by nearly four weeks of hot weather created ideal conditions for anthrax — especially in north-central and northeastern Saskatchewan. By mid-September 2006, more than 900 animals had died — including five horses and one donkey — from anthrax on 174 positive premises in 51 rural municipalities throughout Saskatchewan and Manitoba. CFIA also reported cases of anthrax on a bison farm near Bonnyville, Alta.

  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.

To control the spread of bacterial spores, producers and veterinarians shouldn’t open the carcasses of any animals suspected of dying from anthrax. Once a diagnosis is confirmed, all animals on infected premises are placed under a 21-day quarantine. Carcass disposal is extremely important, and it’s crucial that it’s done very quickly by incineration or by deep burial.

     CFIA vaccinates all animals on quarantined farms and recommends revaccination for at least three years on anthrax-positive premises. Producers on neighbouring farms aren’t required to vaccinate their animals, but during the 2006 outbreak, veterinarians advised producers to vaccinate all herds within 10 kilometres of anthrax-positive premises.

More than 550,000 anthrax vaccine doses were distributed across the Prairies during the summer of 2006. 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 now advise owners of miniature horses and young foals to use other alternatives for preventing the disease. This warning comes after at least nine miniature horses in the region died of an apparent adverse reaction to the anthrax vaccine in the summer of 2006. The deaths are under investigation, but until more confirmed information is available, Clark says it’s best to take preventive precautions with smaller horses — a recommendation that’s now included in the vaccine’s packaged information.

“If you’re in a high risk area, it’s best to take the small horses — the miniatures and young foals — off pasture and give them preserved feed and hay. They should also have access to water from a water bowl, just to be on the safe side,” explains Clark.

 “What producers must keep in mind is that this particular vaccine has saved countless lives over the past 50 years. It’s a tested product that’s well documented to work in cattle, swine, sheep, goats and horses. Severe adverse reactions to this vaccine are highly unusual.”

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.”

       For more information about anthrax, please visit the Farm Animal Council of Saskatchewan’s web site (www.facs.sk.ca) or the Canadian Food Inspection Agency (www.inspection.gc.ca). 

Reprinted with permission of Horse Health Lines, news publication for the Western College of Veterinary Medicine’s Equine Health Research Fund. Visit www.ehrf.usask.ca to sign up for the EHRF e-newsletter.