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Anthrax Fact Sheet

California Veterinary Medical Association

Anthrax is caused by a bacterium known as Bacillus anthracis. When exposed to oxygen, this bacterium forms spores that are very resistant to environmental conditions and can survive for many years, even decades, in the soil. Anthrax is found naturally in California and Nevada, usually infecting cattle, sheep, and goats. One of the most recent group of cases occurred a few years ago in cattle in the Reno area following excavations in an area with a history of previous cases of anthrax. The excavation activity apparently uncovered anthrax spores that had been buried for many years.

Anthrax is caused by a bacterium known as Bacillus anthracis. When exposed to oxygen, this bacterium forms spores that are very resistant to environmental conditions and can survive for many years, even decades, in the soil. Anthrax is found naturally in California and Nevada, usually infecting cattle, sheep, and goats. One of the most recent group of cases occurred a few years ago in cattle in the Reno area following excavations in an area with a history of previous cases of anthrax. The excavation activity apparently uncovered anthrax spores that had been buried for many years.

Cattle, sheep, goats, and other hoofed animals are the most susceptible to anthrax, but most mammals can be infected. Swine are next on the list, and horses are less likely to contract the disease than swine. People, dogs, and cats are even lower on the scale. In other words, it takes a relatively small amount of spores to cause disease in cattle, a larger exposure to cause disease in swine, more in horses and even more to infect people, dogs, and cats. Anthrax is usually not spread from animal to animal, and exposure to an infected animal does not cause infection. New victims acquire the disease through exposure to the spores. Normally, spores are formed when an animal that has died due to anthrax begins to decay and the bacteria are exposed to the oxygen in the air.

In cattle, the usual route of infection is by ingestion of the spores, which leads to the intestinal form of anthrax. The other routes of infection include inhalation of the spores, leading to respiratory anthrax and exposure to breaks in the skin, causing cutaneous anthrax.

The natural route of infection in swine, dogs, and cats is also by ingestion of the spores. In these species, the characteristic signs are swelling of the neck secondary to regional lymph node involvement. This swelling leads to difficulties in swallowing and breathing. The intestinal form of anthrax with severe intestinal involvement sometimes occurs in these animals. Many carnivores seem to have a natural resistance to anthrax, and recovery is not uncommon.

Most strains of anthrax can be treated with a number of antibiotics, including the now well-known Cipro. Other effective antibiotics include penicillin and tetracycline. Treatment should only be initiated when there is a strong suspicion of exposure to the spores. A premature or unwarranted use of antibiotics can lead to many problems, including the formation of resistant forms of bacterial organisms and unwanted side effects of the antibiotic, some of which can be serious.

A vaccine against anthrax is available for cattle and other large animals, but none is available for cats or dogs. The large animal vaccine should not be used in cats and dogs (or people).

January 9, 2017

© 2017 California Veterinary Medical Association

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