What is anthrax?
Anthrax is a naturally occurring disease caused by a spore-forming bacterium called Bacillus anthracis. It can have devastating effects on cattle, sheep, goats, horses and bison.
Laboratory animals, such as guinea pigs, rabbits and mice, are also susceptible to anthrax.
Pigs, dogs and cats are less susceptible. They can be exposed to the bacterium repeatedly before ever becoming infected. Birds and wildlife also appear to be at lower risk for anthrax.
Anthrax is a "reportable disease" under the Health of Animals Act. This means practitioners and laboratories are required to report suspect positive anthrax test results to the Canadian Food Inspection Agency (CFIA).
Is anthrax a risk to human health?
Humans are susceptible to anthrax. However, human cases associated with an animal outbreak are rare if proper precautions are taken when handling and moving affected animals and carcasses.
Humans can become infected by:
- direct or indirect contact with infected animals or carcasses, or
- exposure to infected or contaminated animal products.
There are three types of anthrax that can occur in humans.
- Cutaneous anthrax, the most common, is acquired through breaks in the skin. It causes black, coal-like skin lesions.
- Pulmonary anthrax, which is rare, is acquired by inhaling airborne spores. Signs of this form of the disease resemble the common cold and can progress to severe breathing problems and shock.
- Gastrointestinal tract anthrax is contracted from eating contaminated meat from an animal that died of anthrax. This form of the disease can result in fever, vomiting, diarrhea, weakness, and other gastrointestinal problems.
Most anthrax outbreaks in recent history have been recorded in beef cattle and bison. Anthrax can also occur in dairy cattle. However, the risk of contracting anthrax from milk or dairy products is extremely low.
For more information on the human health implications of anthrax, consult the Public Health Agency of Canada website.
What are the clinical signs of anthrax?
Often the first sign of an anthrax outbreak is one or more sudden deaths in affected livestock. In highly susceptible species like cattle, the time between the onset of mild symptoms (such as feed refusal and/or lower milk production) and death can be a matter of hours.
Animals that do not die suddenly may:
- appear distressed
- have difficulty breathing
- stop eating and drinking
- develop swellings, often under the jaw where the head joins the neck and lower abdominal areas
- have a normal or elevated temperature.
After death, the animal carcass may leak bloody fluids from body openings (rectum, nostrils, mouth, etc.) and bloat rapidly. Rigor mortis might not occur, and blood may not clot.
Where is anthrax found?
Anthrax has occurred nearly worldwide, and has been described in literature since ancient times. Both Canada and the United States have reported sporadic cases of anthrax.
In Canada, anthrax cases have occurred from Alberta to western Ontario, with repeated outbreaks in the Mackenzie Bison Range in the Northwest Territories and in Wood Buffalo National Park in northern Alberta.
How is anthrax transmitted and spread?
The Bacillus anthracis bacterium is shed by an animal that has died of anthrax. This provides a source of infection for other animals. It can be inhaled or it can enter the body through an existing break in the skin or mucous membrane.
Livestock are most commonly infected by ingesting the spores from contaminated pastures, feed or soil (while grazing). Once ingested, the bacterium grows and multiplies in the blood stream.
How is anthrax diagnosed?
Anthrax is diagnosed by examining blood or tissues for the presence of the bacteria. Samples must be carefully collected to avoid environmental contamination and prevent human exposure to the bacteria.
Post-mortem examinations should not be performed on animals suspected to have died from anthrax.
How is anthrax treated?
Anthrax can be treated with antibiotics, such as penicillin. Control and treatment is intended to break the cycle of infection.
However, antibiotics should not be administered during the eight days immediately before or after vaccination, as they interfere with the development of post-vaccination immunity.
Vaccinating livestock is the best protection against anthrax. The Sterne vaccine is the only licensed anthrax vaccine in Canada, and it prevents anthrax in most animals for about one year. It is licensed for use in cattle, sheep, horses, goats and swine. Use of the vaccine in bison is considered extra-label and must be recommended by a veterinarian.
How can livestock be protected?
While vaccinating livestock is the best protection against anthrax, producers should also:
- avoid giving hay that was cut close to the soil or feed that had contact with soil to non-vaccinated animals
- thoroughly clean and disinfect equipment and footwear that may have had contact with contaminated soil
- wash clothes worn when tending to sick animals separately from the rest of the household laundry.
Producers seeking advice on the prevention, diagnosis, treatment or disposal of anthrax cases in their herd are encouraged to contact their private veterinarian.
Information on how to properly dispose of anthrax-infected carcasses, and cleaning and disinfection procedures is also available on the CFIA website.