Anthrax

What is anthrax?

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 a contaminated environment.

Cattle, sheep, goats and horses are highly susceptible to anthrax, as are laboratory animals such as guinea pigs, rabbits and mice.

Other animals such as pigs, dogs and cats, are less susceptible and can sometimes be exposed to the bacterium repeatedly before ever becoming infected. Birds and wildlife also appear to be at a lower risk for anthrax.

Is anthrax a risk to human health?

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 sources of anthrax infection in humans are direct or indirect contact with infected animals or carcasses, and through occupational exposure to infected or contaminated animal products.

In humans, three forms of anthrax occur depending on the route of infection.

Cutaneous anthrax, the most common, is acquired through breaks in the skin and causes black, coal-like skin lesions.

Pulmonary anthrax, which is rare, results from the inhalation of 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.

Although 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?

In highly susceptible species like cattle, the time between onset of mild symptoms (e.g. feed refusal and/or lower milk production) and death can be a matter of hours. Often the first sign of an anthrax outbreak is one or more sudden deaths in affected livestock.

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; and
• 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.

Where is anthrax found?

Anthrax has a nearly worldwide distribution and has been described in literature since ancient times. Both Canada and the U.S. have reported sporadic cases of anthrax.

In Canada, cases of anthrax 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, providing a source of infection for other animals. The bacteria can be inhaled or can enter the body through an existing break in the skin or mucous membrane.

The most common means of livestock infection is ingestion of the spores from contaminated pasture, feed or soil while grazing. Once ingested, the bacterium grows and multiplies in the blood stream.

How is anthrax diagnosed?

Anthrax may be suspected following the sudden death of an animal or observation of any of the clinical signs noted above.

It is diagnosed by examining blood (or other tissues) for the presence of the bacteria. Samples must be collected carefully to avoid contamination of the environment and to prevent human exposure to the bacteria.

A post mortem examination should not be performed on an animal suspected to have died from anthrax.

How is anthrax treated?

The most common form of Bacillus anthracis can be treated with antibiotics, i.e., penicillin. Control and treatment is intended to break the cycle of infection.

Vaccination, used as a control measure prevents anthrax in most animals for about one year. The Stern vaccine is the only licensed anthrax vaccine in Canada, and can be used in cattle, sheep, horses, goats and swine.

Antibiotic treatment interferes with the development of post-vaccination immunity, therefore antibiotics should not be administered during the eight days immediately before or after vaccination.

What is done to protect Canadian livestock anthrax?

The Canadian Food Inspection Agency (CFIA) will impose control measures wherever anthrax is confirmed.

Anthrax is a "reportable disease" under the Health of Animals Act. This means that all suspected cases must be reported to the CFIA for immediate investigation.

How would the CFIA respond to an outbreak of anthrax in Canada?

The CFIA's disease control measures include:

• the removal of animals from an anthrax-contaminated pasture;
• quarantine of the premises;
• proper disposal of carcass and contaminated material;
• disinfection of the premises, and
• vaccination of susceptible animals.

For more information

Contact your CFIA Area office:

Atlantic Area: 506-851-7651

Quebec Area: 514-283-8888

Ontario Area: 519-837-9400

Western Area: 403-292-4301

You can find your local CFIA District office on the CFIA Web site or by consulting the blue pages of your local phone directory.