Anthrax, a disease of mammals and humans, is caused by a spore-forming bacterium called Bacillus anthracis. Anthrax has an almost worldwide distribution and is a zoonotic disease, meaning that it may spread from animals to humans and vice versa. All mammals appear to be susceptible to anthrax to some degree, but ruminants such as cattle, sheep and goats are the most susceptible and commonly affected, followed by horses, and then swine, dogs and cats.

Anthrax is naturally found in many parts of the United States. During their active growth stage, cells of the anthrax bacteria multiply in the lymph nodes of susceptible animals, including humans. When the bacteria cells escape from the animal’s body and are exposed to oxygen, they form spores. These spores are highly resistant to heat, cold, chemical disinfectants, and long dry periods. The B. anthracis spores are reported to survive for years in the environment.

The anthrax organism may be spread within an area by streams, insects, wild animals and birds, and contamination from wastes of infected animals. Ingesting spores, such as in contaminated food or water usually infects animals. Spores can be picked up directly from the soil through grazing or from feed grown on infected soil. Spores may also be present in bonemeal, protein concentrates, animal waste, and tissue and body fluids of infected carcasses. It is also possible for animals to inhale anthrax spores. Bites from flies and other insects that may harbor anthrax have also been reported to be methods for mechanical transmission of the bacteria. Anthrax is not a contagious disease that can spread from one contaminated animal to another.

The disease caused by B. anthracis occurs when spores enter the body, grow, multiply and release toxins. The incubation period of natural infection in animals is typically 3-7 days. Dogs and cats usually show a characteristic swelling of the neck due to lymph node involvement. The swollen lymph nodes cause difficulties in swallowing and breathing. An intestinal form of anthrax associated with severe inflammation of the intestines may sometimes occur in dogs and cats. These species, along with other carnivores, have some natural resistance to anthrax, and recovery from the disease is not uncommon.