How Much Do You Know About Anthrax?

Anthrax is caused by the rod-shaped bacterium Bacillus anthracis. Like most bacteria, B. anthracis reproduces by forming spores. It is primarily a disease of hoofed animals (cattle, sheep, goats), but it can affect humans, as well. In the past, farmers, veterinarians, and workers in the tannery and wool industries have been the people most likely to contract anthrax. Recently, anthrax has become a potential biological warfare weapon. Anthrax in humans takes three forms: inhalation anthrax (breathing in the spores), cutaneous anthrax (spores enter through a cut in the skin and cause lesions), and intestinal anthrax (the spores are ingested through contaminated food). It is not a contagious disease -- it can't be passed from person to person -- like smallpox, another potential biological warfare weapon.

Anthrax is an ancient disease. Biblical scholars believe that the fifth plague of Egypt (pestilence on livestock) was animal anthrax and that the sixth plague (skin boils) was cutaneous anthrax. By the 16th century, doctors were accurately diagnosing anthrax. In the 1870s, pioneering bacteriologist Robert Koch linked anthrax to B. anthracis, the first bacterium clearly linked to a disease. (Koch went on to discover the bacteria that cause tuberculosis and cholera.) Cases of anthrax have been reported all over the world. It occurs only infrequently and sporadically in the United States, and most cases are in cattle. The few cases of human infection have been mostly cutaneous anthrax.

If a person has been exposed to anthrax, but has no symptoms, the CDC recommends that doxycycline, ciprofloxacin, or levofloxacin be prescribed. The person might also need to be immunized against anthrax if the exposure was to potentially airborne B. anthracis spores.

The longer spores last, the more likely it is that the bacteria will survive. Anthrax spores can survive for more than 50 years in dry soil, such as that found in the Midwest and Southwest. Anthrax spores also can survive for long periods inside buildings and on equipment. Because spores are extremely difficult to kill with standard disinfectants and sterilizing temperatures, it is difficult to impossible to clean up contaminated equipment and buildings. Some contaminated buildings have been dismantled, with portions incinerated and the remainder buried.

The largest human anthrax outbreak ever reported occurred in Zimbabwe during a civil war. In the outbreak, 9,593 cases were reported and 149 deaths. Most of the cases were cutaneous (skin) anthrax, rather than inhalation or intestinal anthrax. This occurred despite the butchering, eating, and disposing of cattle that had died of anthrax.

With treatment, cutaneous anthrax is not fatal. Although 20 percent might seem high, the fatality rate of untreated inhalation anthrax approaches 100 percent.

A building contaminated by anthrax spores is extremely difficult to decontaminate. The CDC successfully decontaminated the Hart Building in Washington, D.C., with chlorine dioxide gas. This gas had proved quite effective against B. subtilis spores (a close cousin of B. anthracis), but until the Hart Building, it was unknown whether it would work on anthrax spores spread throughout a building.

The first anthrax vaccine was developed in 1881 by the French microbiologist Louis Pasteur. Although microbiology was a relative new and primitive science, Pasteur was able to develop an effective vaccine even with limited tools. Vaccine development for anthrax has continued. In the United States, a live organism vaccine (the Sterne vaccine) is available for animals, and a safe and effective antitoxin vaccine is available for human use. Currently, only U.S. military personnel are immunized against anthrax. If anthrax becomes a significant problem, the civilian population in this country can be immunized.

There appear to be no long-term complications from being vaccinated with the type of anthrax vaccine used by the U.S. military. Although some recruits have refused to be vaccinated and others have reported post-vaccination problems, no consistent complaint has been linked to vaccination. Considering the severity of inhalation anthrax and the fact that the vaccine is more than 98 percent effective, there should be little objection to vaccination. Anthrax is given as a series of six injections. After the first injection, two others are given, two and four weeks later. Boosters are then given at six, 12, and 18 months. It takes 18 months to become fully immune, although immunity begins building after the first injection.

Dogs and cats seem to be more resistant to anthrax than other animals. This should help pet owners worry a little less about their pets.