Anthrax: How It Kills

Seven years ago Americans learned to fear anthrax as a white powder in the mail that claimed lives, forced the post office to change the way it handles letters and sparked contamination scares across the country.

The anthrax attacks have returned to the news after biodefense researcher Bruce E. Ivins of the government labs at Fort Detrick, Md., apparently committed suicide as prosecutors prepared to seek charges against him in the deadly 2001 attacks.

The poisoned mail killed five people across the country and sickened 17.

The spores that cause anthrax, Bacillus anthracis, occur widely in soil and the skin form of the infection used to be common, especially among livestock and people who work with the animals. It can be treated with antibiotics.

The mailed form proved deadly because, once the contaminated letters were opened, the spores were inhaled, settling in the lungs, causing a hard-to-diagnose infection that is almost impossible to cure once symptoms start.

Experts estimate that 8,000 to 10,000 spores taken into the lungs can cause inhaled anthrax. The infection is not contagious.

Shortly after the attacks, there were reports that the anthrax spores in the letters contained additives and had been subjected to sophisticated milling -- both techniques used in anthrax-based weapons -- to make them more lethal. But FBI officials later said the early media reports of weaponized anthrax were misconceptions.

Infection with the skin form of the disease can result from substantially fewer spores.

On the skin, the ailment starts after three to five days with a small, 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.

The usual treatment is a common antibiotic, such as penicillin, doxycycline or Cipro. These medicines are extremely effective.

Left untreated, perhaps 5 percent of skin cases progress to a dangerous bloodstream infection, which is almost always fatal, according to medical experts.