Causative agent: Bacillus anthracis
Anthrax most commonly causes sudden death. If the carcass of a dead animal is not opened after death, putrefaction will destroy the bacteria. If the carcass is opened to the air, the bacteria will produce resistant spores that may survive in the environment for up to 30 years (9). Infection is thought to occur by ingestion of spores present in recently disturbed soil or hay. Spores can be spread by streams, insects, birds, dogs and other carnivores (9). Humans can contract anthrax if they eat infected meat or through bacterial contamination of skin scrapes or lacerations suffered while processing or performing a postmortem on an infected carcass. Anthrax has been described in bison from Canada (2,3,4,5) and the USA (6,7).
Clinical Signs:
The following are some clinical signs associated with anthrax in bison (2,3,4,5,6,7):
- this is usually a very rapidly fatal disease.
- clinically affected bison will be moribund. They often stand with their head down, and are unresponsive.
- they may be lame, stagger or have a stiff legged gate and they may be reluctant to move, walking with great difficulty.
- affected animals will often have edematous swellings of the preputial or umbilical region.
- occasionally, a bison may survive the disease.
Diagnosis:
The diagnosis is most commonly made on postmortem examination of the carcass. Swabs may be taken of the exudate from any of the body orifices and examined microscopically for the presence of the bacteria, which have a characteristic rectangular “box-car shape”. Swabs can be sent to a diagnostic pathology laboratory for bacterial culture and identification.
Postmortem findings:
- the most common accompanying history is sudden death.
- care should be taken not to perform a postmortem dissection without first examining exudate from the mouth, nose, ears, or anus for the presence of B. anthracis organisms.
- the carcass bloats quickly after death, and has a sawhorse configuration.
- there may be exudation of dark tarry blood from body orifices.
- the blood of infected bison may not clot after death.
- the spleen and lymph nodes are typically enlarged.
Treatment:
There is no effective treatment for anthrax. Affected animals usually die. If an animal is found alive, high doses of systemic antibiotics (penicillins) may be tried.
Control:
Anthrax is a reportable disease in Canada. If the disease is suspected the Canadian Food Inspection Agency (CFIA) must be notified immediately. Members of the CFIA will destroy, or bury carcasses and disinfect the ground on which they were found. The bison on the ranch will be vaccinated and the ranch will be quarantined.