Despite the germ's terrifying reputation, anthrax infections on the skin are rarely fatal, and most people get better even without treatment.
The most feared use of anthrax as a bioterrorist's weapon is spraying it through the air so it is breathed into the lungs, causing a hard-to-diagnose infection that is almost impossible to cure once symptoms start.
The case confirmed at NBC News in New York City on Thursday was a much less aggressive form of anthrax, although both are caused by the same germ. That variety, called cutaneous anthrax, results when anthrax spores get through a scratch or other break in the skin and cause a sore.
"The main thing for people to remember is, if you get cutaneous anthrax, it doesn't mean you will die from it," said Dr. Philip Carter, an expert at North Carolina State University's veterinary school.
Most people get better even without treatment. And taking standard antibiotics cures virtually everyone.
Anthrax, whether the inhaled or skin variety, is caused by spores of Bacillus anthracis, primarily a livestock disease.
On the skin, the ailment starts after three to five days with a nondescript, painless blister that is red around the edges. A day or two later, this becomes an open sore that is especially recognizable because it is black. Eventually, this dries up and leaves a black scab, which falls off after a week or two.
People typically seek treatment, and the usual approach is a common antibiotic, such as penicillin, doxycycline or Cipro. These medicines are extremely effective.
"Antibiotics and a clean gauze patch to cover it should take care of you," said Dr. Philip Hanna of the University of Michigan.
Left untreated, he said, perhaps 5 percent of cases progress to a dangerous bloodstream infection, which is almost always fatal.
Health and Human Services Secretary Tommy Thompson cautioned against hoarding antibiotics in case of anthrax exposure. "We have enough for everyone who needs it," he said.
The skin form of anthrax accounts for 95 percent of all anthrax cases in the United States. Nevertheless, it is very rare, usually causing only a case or two a year.
Anthrax is mainly a disease of grazing animals, and cutaneous anthrax is largely confined people whose skin is exposed to the bacteria, such as ranchers, hide workers and veterinarians.
One typical case, described in August by the Centers for Disease Control and Prevention, involved a rancher in North Dakota who developed a telltale black sore the size of a quarter on his cheek. It was diagnosed as anthrax and traced to an outbreak of the bacterial disease among cattle. Eventually 157 cows died on 31 farms. The rancher recovered.
Cutaneous anthrax was more common during the early 20th century, when the bacteria sometimes entered the United States on imported animal hides. One common source of the disease was shaving brushes made from infected horse hair.
Typically, people get the anthrax sores on the head, neck and arms. Usually, the sores do not spread beyond the initial site of the bacteria's entry into the body, and they are not contagious.
Experts estimate that 8,000 to 10,000 spores taken into the lungs can cause inhaled anthrax. Dr. David Fleming, the CDC's deputy director, said infection with the skin form of the disease can result from "substantially less" spores. The amount would be too tiny to see with the naked eye.
Medical Editor Daniel Q. Haney is a special correspondent for The Associated Press.
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