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June 2001
Vol. 4, No. 6, p 56.
diseases and disorders

Woolsorter’s disease

opening art

Anthrax, as it is more commonly called, is caused by the Gram-positive, spore-forming bacteria Bacillus anthracis. Woolsorter’s disease was also once known as ragpicker’s disease; its most common form in humans is cutaneous infection via the injured skin or mucous membranes of agricultural or industrial workers associated with infected animals or animal products. In 1877, the bacillus was the first bacterium shown to be the cause of a disease—one of the origins of the famous (Robert) Koch’s postulates. Along with mad cow disease, toxoplasmosis (see “Diseases and Disorders”, MDD, May 2001), and the black plague (see “The Time Line”, MDD, Nov/Dec 2000),anthrax is one of many animal blights with a direct impact on human health. The disease is surprisingly common and is endemic in the United States.

Infection occurs through the skin or by inhalation or ingestion of bacterial spores. Intestinal and pulmonary anthrax are the most deadly. The latter usually results in death 1–2 days after the onset of acute symptoms. Treatment with antibiotics such as penicillin is generally effective after initial exposure and can protect against growing bacilli, but it will not destroy the spores themselves.

The bacteria can propagate wildly and stimulate effusions of blood and fluids in various organs and body cavities (>109 bacteria/mL of blood is commonplace). This is followed by prostration of the victim and organ failure (see box, “A lethal combo”). One of the reasons anthrax is such a deadly pathogen may be because its evolution has made it dependent on the death of the host for propagation. Once death ensues in nature, the animal’s carcass rots in the field, exposing the bacteria crowded in the bloodstream to the open air. This stimulates spore formation, which is the main transmissible source of the disease. Spores can survive for decades in contaminated soil from which they can ultimately be inhaled or ingested by herbivores, which starts the cycle over again. Because anthrax requires the death of its host to effect transmission, few evolutionary stops exist compared with disease organisms that depend on the host staying alive—at least long enough for transmission.

A lethal combo
B. anthracis spore

Metabolically, Bacillus anthracis employs three interacting proteins to destroy its host: edema factor (EF), lethal factor (LF), and protective antigen (PA). EF is an adenylate cyclase that stimulates massive accumulations of cyclic adenosine monophosphate in eukaryotic cells. LF is a protease that inhibits mitogen-activated protein kinase. PA binds to receptors on mammalian cells and is cleaved to produce a binding and translocating factor that allows the other two proteins to enter, forming the two exotoxins that cause the most devastating effects of the disease. Edema toxin is formed from the combination of EF and PA; lethal toxin stimulates severe necrosis and results from the binding of PA and LF. Toxin production leads to tissue destruction and ultimately organ failure.

Vaccine controversy

Normally, anthrax vaccination is only recommended for workers in danger of exposure—especially farmworkers and veterinarians in rural practice. But anthrax has also been a staple of the biological warfare arsenal for nearly 60 years; thus, it is increasingly a military concern. Ever since the Gulf War and the decision by the U.S. military to conduct mandatory anthrax vaccinations of its personnel, there has been public controversy over the safety and efficacy of the vaccine. A recent U.S. Supreme Court decision upheld the right of the military to enforce its anthrax vaccination policy. Studies conducted by the Centers for Disease Control and Prevention (CDC) found no link between anthrax vaccination and adverse reactions, including the purported “Gulf War Syndrome”.As part of a congressionally mandated CDC Anthrax Vaccine Research Program, new studies on rhesus monkeys are planned to determine the vaccine’s effectiveness, especially against aerosol delivery, the most likely terrorist scenario.

The only approved anthrax vaccine in the United States is produced from a cell-free filtrate of bacterial cultures. Vaccination generally involves a 6-dose schedule at 0, 2, and 4 weeks with boosters at 6, 12, and 18 months. Problems with vaccine supply have also recently been an issue—BioPort Corp., the Lansing, MI, company that makes the vaccine, was unable to produce sufficient doses to meet demand in 2000.For the CDC’s view of the vaccine issue, visit the CDC Web site, especially www.cdc.gov/mmwr/preview/mmwrhtml/rr4915a1.htm.


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