Anthrax

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Overview, Causes, & Risk Factors

Anthrax is caused by the bacterium Bacillus anthracis. While anthrax commonly affects hoofed animals such as sheep and goats, humans may acquire this disease as well. Humans can acquire anthrax through contact with animal hides or hair, bone products, and wool, as well as contact with infected animals. Historically, the populations most at risk for anthrax include farm workers, veterinarians, and tannery and wool workers.

Anthrax is a potential agent for use as a biological weapon or bioterrorism. While at least 17 nations are believed to have a biological weapons program, it is unknown how many nations or groups are working with anthrax. Most bioterrorism experts have concluded that it is technologically difficult to use anthrax effectively as a weapon on a large scale.

Cutaneous anthrax is an infection of the skin with anthrax. The disease occurs after the bacteria contact skin cuts or abrasions. Usually within two weeks, an itchy skin lesion develops (similar to an insect bite). This lesion may later blister and then break down, resulting in a black ulcer which is frequently painless. The skin lesion is usually surrounded by significant swelling. Sometimes painful lymph nodes may develop. A scab is often formed which then dries and falls off within two weeks. In 20% of UN-treated individuals, the infection may spread through the bloodstream and become fatal. However, in most individuals who receive appropriate treatment, death from cutaneous anthrax is extremely rare.

Inhalation anthrax develops when anthrax spores enter the lungs. A person may have spores in the nasal passages (which indicates exposure), but that doesn't mean they will get the disease. In fact, antibiotic therapy following known or suspected exposure can help prevent the disease. In order for a person to develop the actual disease, the spores must germinate -- a process which may take several days, or even up to 60 days to occur. The spores move to the lymph nodes, and once they germinate, lead to the release of several toxic substances (toxins). This results in hemorrhage, swelling, and tissue death. The main form of inhalation anthrax includes hemorrhagic infection of the lymph nodes in the chest (hemorrhagic mediastinitis). Up to half of affected individuals may also have a hemorrhagic meningitis.

There are usually two stages of inhalation anthrax -- the first stage can last from hours to a few days and is similar to a flu-like illness with fever, headache, cough, shortness of breath, and chest pain. The second stage often develops suddenly and is notable for shortness of breath, fever, and shock. This second stage is highly fatal in up to 90% of individuals because of the build-up of toxins.

The gastrointestinal form of anthrax (gastrointestinal anthrax) occurs with ingestion of contaminated meat. Disease usually develops within one week and can affect the upper portion of the gastrointestinal tract (mouth and esophagus) or the intestines and colon. Infection in both of these areas may result in spread of the infection by the bloodstream and can result in death.