Merck Manual

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Pet Owner Version

Anthrax in Dogs


Martin E. Hugh-Jones

, VetMB, MPH, PhD, MRCVS, School of Veterinary Medicine, Louisiana State University

Reviewed/Revised Jun 2018 | Modified Oct 2022

Anthrax is an often fatal infectious disease that can infect all warm-blooded animals, including dogs and humans. Underdiagnosis and unreliable reporting make it difficult to estimate the true rate of occurrence of anthrax worldwide; however, anthrax has been reported from nearly every continent. Throughout the past hundred years, animal infections have been seen in nearly all states, with the highest frequency in the Midwest and West. Presently, anthrax is found most often in west Texas and northwest Minnesota. It is also found sporadically in south Texas, Montana, eastern North and South Dakota and only occasionally seen elsewhere. Anthrax received much attention in 2001 in relation to the terrorist attacks on the United States because of its potential use as a biological weapon.

Anthrax is caused by infection with bacteria known as Bacillus anthracis. This bacterium forms spores, which make it extremely resistant to environmental conditions, such as heating, freezing, chemical disinfection, or dehydration that typically destroy other types of bacteria. Thus, it can persist for a long time within or on a contaminated environment or object. Livestock may consume the spores while grazing; however, the most common source of infection in dogs is from raw or poorly cooked contaminated meat or contact with the blood, tissues, or body fluids of infected animals that harbor spores. Although the inhalation of anthrax spores is a concern in humans, the dog appears to be quite resistant to infection by this route of exposure. A skin form of anthrax exists in humans, but this route is also thought to be of minimal significance in dogs.

After exposure to the bacteria, the typical incubation period is 3 to 7 days. Once the bacteria infect an animal or human, the organisms multiply and spread throughout the body. They produce a potent and lethal toxin that causes cell death and breakdown of the tissues infected with the bacteria. This results in inflammation and organ damage and can eventually lead to organ failure. The bacteria spread throughout the body through the blood and lymphatic (immune) system.

Dogs may develop sudden, severe (acute) blood poisoning after ingesting Bacillus anthracis bacteria. This may lead to a rapid swelling of the throat, and sudden death. More often, a mild, chronic form is seen, in which dogs show generalized signs of illness and gradually recover with treatment. Intestinal involvement is seldom recognized because the signs (such as loss of appetite, vomiting, diarrhea or constipation) are so nonspecific.

A diagnosis based on signs is difficult because many infections and other conditions (such as poisoning), may have signs similar to anthrax. Diagnosis thus requires laboratory analysis of blood samples from the potentially infected individual to confirm the presence of the bacteria.

Anthrax is controlled through vaccination programs in large animals (such as cattle), rapid detection and reporting, quarantine, treatment of any animals exposed to the bacteria, and the burning or burial of suspected and confirmed fatal cases. In most countries, all cases of anthrax must be reported to the appropriate regulatory officials. Cleaning and disinfection of any bedding, cages, or other possibly contaminated materials is necessary to prevent further spread of the disease. If a pet is exposed to anthrax, the fur should be decontaminated to avoid transmission to humans. Because anthrax spores are resistant to many disinfectants, check with a health official as to proper decontamination procedures.

Human cases of anthrax may follow contact with contaminated animals or animal products. Anthrax is not directly communicable by usual social contact from one infected animal to another animal, between animal and person, or person to person, even in the case of anthrax pneumonia. For infection to occur, spores must gain access to the new victim by ingestion, inhalation, or through open wounds. When transmission occurs between individuals it is usually through exposure to infected tissue or body fluids. Therefore, people should use strict precautions (wearing gloves, protective clothing, goggles, and masks) when handling potentially infected animals or their remains. If a person has inhaled anthrax, preventive treatments are available. In addition, people who have eaten raw or undercooked meats that were contaminated with anthrax may require preventive treatments.

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