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Flood A Precursor To Anthrax

By any measure, the 2011 snow pack makes flooding in many areas on the Prairies almost a certainty. Any flooded land in anthrax endemic areas should be considered high risk and cattle grazing low, wet, or previously flooded land should definitely be vaccinated.

The warning comes from veterinary authorities across Minnesota, the Dakota’s and the Canadian Prairies.

Anthrax is a highly fatal disease that can affect all mammals, including humans. The disease is caused by a spore-forming bacterium called Bacillus anthracis. Animals generally acquire the disease from grazing grassland and mixed forested regions contaminated by spores. Cattle, bison, sheep, goats and horses are highly susceptible to anthrax. Other animals such as pigs, dogs, and cats are less susceptible, but can sometimes be infected through repeated exposure. Birds and wildlife, other than bison, are at a lower risk of contracting anthrax.

When exposed to environmental conditions outside an infected carcass, Bacillus anthracis produces highly resilient spores that remain viable in soil for many years (perhaps a century or more). Ingestion of spores from soil as animals graze starts another cycle of infection. Wind erosion during drought, flooding and any activity that disturbs topsoil can all bring anthrax spores in close contact with grazing animals. Flooding of endemic areas percolates spores buried in soil toward the surface and in contact with grazers. Soil erosion compounds the situation and may actually play a role in the transport and seeding of spores into areas previously unaffected. Once ingested, activated anthrax spores revert to bacteria that rapidly multiply releasing powerful toxins that cause clinical disease, which often culminates in death. Some researchers believe Tabanid species (large biting flies) can play a role in transmitting anthrax during outbreaks.

Humans are susceptible to anthrax infection; however it is rare to find a human case of anthrax associated with an animal outbreak if proper precautions are taken during the handling and movement of affected animals and carcasses. The principal source of anthrax infection in humans is direct or indirect contact with infected animals or carcasses, and through occupational exposure to infected or contaminated animal products.

Although most anthrax outbreaks in recent history have been recorded in beef cattle and bison, anthrax can also occur in dairy cattle and horses.

In highly susceptible species like cattle, the time between the first onset of symptoms and death can be a matter of hours. Often the first sign of anthrax in a herd is discovery of dead animals that appeared normal just hours before.

Animals discovered before dying appear distressed and may have difficulty breathing. Most stop eating and drinking and often develop swellings under the jaw where the head joins the neck and lower abdominal areas. Body temperature may or may not be elevated. After death, the animal carcass may leak bloody fluids from the rectum, nostrils or mouth and bloat rapidly. Rigor mortis might not occur.

Anthrax can appear similar to other potential causes of sudden death in cattle like blackleg and malignant edema.

Suspect carcasses must be handled carefully to prevent accidental spread of anthrax spores to the environment and humans. For that reason producers should contact a veterinarian when animals die suddenly. Anthrax is diagnosed by examining blood (or other tissues) for the presence of the bacteria and samples must be collected carefully to avoid contamination. Normally, a post mortem is not performed on animals suspected of anthrax.

Anthrax is found worldwide and been described in historical documents since ancient times. In Canada, cases have occurred from Alberta to western Ontario, with repeated outbreaks in the Mackenzie Bison Range in the Northwest Territories and Wood Buffalo National Park in northern Alberta. Manitoba, Saskatchewan and Alberta have all had problems with anthrax in domestic herds. The Canadian Food Inspection Agency recommends that all ranchers on the Prairies vaccinate cattle against anthrax, to curb recent outbreaks that have been the worst in decades.

Vaccination prevents anthrax in most animals for about one year. The attenuated, live spore (Sterne strain) vaccine is licensed in Canada, and can be used in cattle, sheep, horses, goats and swine. While the most common form of Bacillus anthracis can be treated with antibiotics like penicillin, animals receiving any form of antibiotic treatment at the time of, or shortly after, vaccination may not respond adequately to vaccine. Animals as young as two weeks of age may be expected to respond fully to the vaccine, although risk of disease is low until animals are exposed to spores through grazing.

Anthrax is a “reportable disease” under the Health of Animals Act. All suspected cases must be reported to the CFIA for immediate investigation. The Canadian Food Inspection Agency (CFIA) will impose control measures wherever anthrax is confirmed.

This year’s risk of anthrax is high in certain areas. Producers at risk need to discuss the pros and cons of anthrax vaccination with a veterinarian. The wait-and-see approach with anthrax is often a regrettable choice. Dr.RonClarke

About the author

Columnist

Dr. Ron Clarke

Dr. Ron Clarke prepares this column on behalf of the Western Canadian Association of Bovine Practitioners. Suggestions for future articles can be sent to Canadian Cattlemen ([email protected]) or WCABP ([email protected]).

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