Anthrax

Causative Agent

• A zoonotic disease caused by infection with the bacteria Bacillus anthracis.

• B. anthracis bacteria are highly effective at causing disease because of several factors:

  • highly resistant, infectious spores that are capable of surviving outside of the host may be produced

  • toxins are released in the blood of the host organism while the bacteria are undergoing rapid reproduction

  • it is highly infectious to humans

Geographic:

• Worldwide distribution; may be locally common.

• In Canada, anthrax has been reported in wood bison in the Northwest Territories and in northeastern Alberta.

Seasonality:

• May occur throughout the year, but most often in the late summer.

Hosts:

• Mammalian herbivores have a higher susceptibility to anthrax than carnivores, likely due to a more effective response from the immune system of carnivores.

• Wild mammals in North America that have been confirmed to be susceptible to anthrax include:

  • wood bison

  • white-tailed deer, moose

  • bobcat, cougar

  • raccoon

  • mink

• Humans are also susceptible to anthrax.

Transmission:

• Transmission in wildlife and in humans occurs in one of three ways:

  • cuts in the skin (cutaneous)

  • inhalation

  • ingestion

• Infected animals as well as “carriers” of the disease can shed spores in urine and feces.

• In wildlife, anthrax outbreaks typically occur in dry summers following periods of rain.

• Dry weather usually forces grazing animals to feed closer to the ground where spores are often concentrated. Exposure typically occurs through inhalation or ingestion of dust.

• Transmission among susceptible animals may also occur through flies and mosquitoes.

• Humans can contract anthrax from contact with infected animals through either:

  • cuts or scratches in the skin

  • the eyes, nose or mouth

  • inhaling spores from contaminated objects such as hides of infected animals

  • eating undercooked meat from an infected animal

Life Cycle:

• The oxygen and nutrient-rich blood of a warm-blooded host effectively prevents other types of bacteria within the host from competing with anthrax bacteria for resources.

• When a host dies, and oxygen is no longer transported in the blood, B. anthracis bacteria become dormant .

• Other types of bacteria from the gastrointestinal tract of the host animal begin the process of decomposition and can destroy remaining B. anthracis bacteria if the carcass remains intact.

• Scavenging birds and mammals may open the carcass, dispersing anthrax bacteria which, given the correct environmental conditions, form spores that are infectious to other animals or humans.

Signs and Symptoms

Animals:

• Within hours or days after exposure, infected animals may show signs of fever, debilitation, breathing difficulties, disorientation, and ultimately death.

• Toxins produced by bacteria in the blood are transported throughout the body. These toxins cause a reduction in oxygen in the blood, edema, kidney failure, shock, and ultimately death.

• A frothy discharge may be observed from the nose in addition to bloody discharges from other body orifices.

Humans:

• Signs of gastrointestinal (ingestion) anthrax include:

  • fever, loss of appetite, vomiting and diarrhea.

• Signs of inhalation anthrax include:

  • fever, sore throat and general ill-feeling that may be followed by breathing difficulties – this is the most serious type of anthrax infection.

• Signs of cutaneous (skin) anthrax include:

  • a small painless bump that often appears on the skin which becomes a blister and then an ulcer with a black centre. In humans, this is the most common type of anthrax infection and can be treated with antibiotics.

Meat Edible?

• Meat from infected animals should not be consumed nor fed to dogs. Carcasses should not be opened or cut into.

Human Health Concerns and Risk Reduction

• Anthrax is a potentially fatal zoonotic disease; all appropriate precautions should be taken to avoid exposure.

• The carcass of a dead animal suspected of having anthrax SHOULD NOT BE OPENED OR TOUCHED! Wild bison are the most likely to be found; however, cattle are occasionally reported as well.

• REPORT ANY SUSPECTED CASES OF ANTHRAX TO THE NEAREST CONSERVATION OFFICER OR HEALTH AUTHORITY.

• For further information on human health concerns and anthrax, please refer to anthrax information provided at the URLs of Health Canada or that of the US Centres for Disease Control and Prevention and follow the appropriate links.

Gates, C. C., B. Elkin, and D. Dragon. 2001. Anthrax. Pp. 396-412 in E. S. Williams and I. K. Barker (eds.), Infectious diseases of wild mammals. 3rd Ed. Iowa State University Press, Ames, IA. 

Common Wildlife Diseases and Parasites in the NWT and Nunavut - anthrax information

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