Anthrax in Dogs

By Krista Williams, BSc, DVM, CCRP; Ernest Ward, DVM

I have heard about anthrax in people. Should I be concerned for my dog?

You may have heard anthrax discussed as a potential weapon in bio-terrorism. Most mammals are susceptible to anthrax, but different animals have different levels of susceptibility. In general, herbivores are more susceptible to anthrax than carnivores. Under normal circumstances, cases of anthrax in dogs are very rare and dogs seem relatively resistant to infection.

What causes anthrax?

Anthrax is an infection caused by a bacterial microorganism, Bacillus anthracis. This type of bacterium can develop small spherical bodies called spores within the bacterial cell. These spores, each of which can develop into a new anthrax bacterial cell, are much more capable of surviving in the environment than the more fragile parent cell. Additionally, these spores are more resistant to disinfectants. Spores may survive in the environment for many years; some reports indicate that spores may survive up to 40 years under certain conditions. Fortunately, it takes a large number of spores to cause an infection that result in clinical signs of anthrax.

Is anthrax a new disease?

No, anthrax has been described in the medical and veterinary literature for hundreds of years. It occurs in all parts of the world as a sporadic disease in farm animals and occasionally in wild animals.

How is anthrax spread?

Anthrax is not normally contagious from animal to animal. Most livestock infections occur by inhalation or ingestion of spores from a pasture contaminated by a decomposing infected carcass.

"In predators such as dogs, ingestion of infected meat is the usual route of infection."

In predators such as dogs, ingestion of infected meat is the usual route of infection. In people, anthrax has typically been diagnosed in farm workers, veterinarians, and slaughterhouse personnel who have handled infected carcasses. Even then, it usually takes a high dose of spores to cause more than a local skin infection. In the past, sheep fleeces were a common source of anthrax spores and anthrax in those workers was called "wool-sorters disease".

What are the symptoms?

Anthrax can cause different types of disease. A dermatological (skin) form of anthrax, most common in people that come into contact with the anthrax organism or its spores, results in local inflammation and the formation of black pustules on the skin. An intestinal form, which occurs when large numbers of organisms are ingested and the intestinal lining becomes inflamed, causes bloody diarrhea. A pneumonic form develops when large numbers of the anthrax organism or spores are inhaled into the lungs, causing pneumonia and respiratory problems. The infection can have a generalized form, affecting most or all body systems, including the brain, and causing fever, poor appetite, and weight loss.

"The rare cases reported in pet animals have usually been the intestinal form of anthrax..."

The rare cases reported in pet animals have usually been the intestinal form of anthrax, caused by eating infected meat. Affected pets develop acute gastroenteritis with vomiting and diarrhea. The throat may be swollen and there may be visible swelling of the neck, extending to the face and head. The tongue and lips may also be ulcerated. Diagnosis is made by culturing the anthrax organism.

How can anthrax be treated?

The anthrax bacterium is susceptible to a number of antibiotics. Currently the antibiotics of choice are penicillins, enrofloxacin, and tetracyclines. Ciprofloxacin has also shown efficacy; however, absorption of this drug is variable in dogs so higher dosing and/or combination with other antibiotics may be needed. Treatment is highly effective in the early stages of infection.

Can my dog be vaccinated against anthrax?

There is currently no commercial anthrax vaccine licensed for use in dogs, although a number of vaccines of varying effectiveness have been produced. In some parts of the world, domestic livestock and humans employed in high-risk occupations may be vaccinated.

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