Anthrax is a zoonotic disease caused by toxins from the bacteria Bacillus anthracis (Stitt, 2011). B. anthracis is highly effective at causing disease. It produces highly resistant, infectious spores that can survive outside the host for long periods of time. While the bacteria are undergoing rapid reproduction, they release toxins in the blood of the host organism. Anthrax is highly infectious to humans (Miller et al, 2003).

Anthrax is rare in the United States, but sporadic outbreaks do occur in wild and domestic grazing animals such as cattle or deer. Anthrax is most common in agricultural regions of Central and South America, sub-Saharan Africa, central and southwestern Asia, southern and Eastern Europe, and the Caribbean (National Center for Emerging and Zoonotic Infectious Diseases).  Anthrax outbreaks may occur throughout the year, but are most common in the late summer. In wildlife, anthrax outbreaks typically occur in dry summers following periods of rain. Dry weather may force grazing animals to feed closer to the ground where B. anthracis spores are often concentrated (Miller et al, 2003).

Mammalian herbivores are more susceptible to anthrax than are carnivores, likely due to a more effective response from the immune system of carnivores (Miller et al, 2003). The most common wildlife hosts are bison and cervids (Stitt, 2011). Wild mammals in North America that have been confirmed to be susceptible to anthrax include bison, white-tailed deer, moose, bobcat, cougar, raccoon, and mink (Miller et al, 2003).

Wild animals can become infected when they breathe in or ingest spores in contaminated soil, plants, or water (National Center for Emerging and Zoonotic Infectious Diseases). Transmission among susceptible animals may also occur through flies and mosquitoes (Miller et al, 2003).

In most cases, animals with anthrax are simply found dead, and anthrax may be suspected when animals are found dead, are bloated, and do not develop rigor mortis.  In addition, blood may be observed coming from body orifices (AVMA).  

Signs of the illness usually appear 3-7 days after the anthrax spores are inhaled or swallowed but may occur sooner if a large number of spores are inhaled. Once symptoms begin, animals usually die within two days. Seriously affected animals may stagger, have difficulty breathing, tremble, and finally collapse and die within a few hours. Animals with less serious cases may have a rise in temperature, a period of excitement followed by staggering, depression, unconsciousness, difficulty breathing, convulsions, and death (Texas Health and Human Services).

Anthrax is a potentially fatal bacterial infection with worldwide distribution. People get infected with anthrax when spores get into the body. When anthrax spores get inside the body, they can be “activated” and multiply, spread out in the body, produce toxins (poisons), and cause severe illness. This can happen when people breathe in spores, eat food or drink water that is contaminated with spores, or get spores in a cut or scrape in the skin. It is rare for people in the United States to get infected with anthrax (National Center for Emerging and Zoonotic Infectious Diseases).

Most people who get sick from anthrax are exposed while working with infected animals or animal products such as wool, hides, or hair. Inhalation anthrax can occur when a person inhales spores that are in the air (aerosolized) during the industrial processing of contaminated materials, such as wool, hides, or hair. Cutaneous anthrax can occur when workers who handle contaminated animal products get spores in a cut or scrape on their skin (National Center for Emerging and Zoonotic Infectious Diseases, CDC).  Anthrax is not transmitted from person to person. If you suspect contact with material potentially contaminated with anthrax, wash your hands with soap and water and immediately contact your health care provider (Montana DPHHS and Montana DoL). department.The carcass of a dead animal suspected of having anthrax should not be opened or touched. Report any suspected cases of anthrax in wildlife to the nearest FWP wildlife biologist or wildlife manager.

Information about Antrhax in humans can be found on the CDC website and from the Montana DPHHS website.

Is Meat from Infected Animals Safe to Eat?

People who eat raw or undercooked meat from infected animals may get sick with gastrointestinal anthrax. In the United States, gastrointestinal anthrax has rarely been reported. The normal hunting season in Montana occurs in fall and winter when of cases of anthrax traditionally do not occur. Anthrax causes rapid death of infected animals, and diseased animals appear very ill before they die. Hunter should harvest only animals that appear healthy, should wear hunter gloves and long sleeves when field dressing, and thoroughly cook meat before eating it (Texas Health and Human Services).  If a harvested animal is suspected to be sick, report to local FWP staff for guidance as soon as possible after harvest.

Miller, M.J.R., R.D. Dawson, and H. Schwantje. 2003. Manual of Common Diseases and Parasites of Wildlife in Northern British Columbia. University of Northern British Columbia.

Montana Department of Public Health and Human Services and Montana Department of Livestock. Montana One Health. Anthrax. June 2020. Volume 10. Issue 2. https://liv.mt.gov/_docs/Animal-Health/Newsletters/MOH_Anthrax_2020_2nd%20quarter.pdf

National Center for Emerging and Zoonotic Infectious Diseases. U.S. Department of Health and Human Services. Center for Disease Control and Prevention. “Guide to Understanding Anthrax” https://www.cdc.gov/anthrax/pdf/evergreen-pdfs/anthrax-evergreen-content-english.pdf. Accessed 4 January 2022.

Stitt, Tyler. 2011. Diseases You Can Get From Wildlife - A Field-guide for Hunters, Trappers, Anglers and Biologists. British Columbia Ministry of the Environment.

Texas Department of State Health Services.  Texas Health and Human Services. “Anthrax FAQ’s”.   https://www.dshs.texas.gov/IDCU/disease/anthrax/information/FAQs.aspx. Accessed 4 January 2022.