Anthrax has been making many Americans nervous lately, but it is rare in this country, in part because of measures taken on ranches and in factories, experts say. 

From 1900 to 1976, only 18 cases of the inhaled version — the most dangerous — were reported in the United States. No more appeared until the highly publicized incident in Florida this month in which a newspaper worker died. 

In the early 1900s, the nation had about 200 cases a year of a less threatening form in which the bacterium infects the skin — the type that recently infected an NBC News employee. 

By the close of the century, reports had dwindled to around a case every other year. There weren't any between 1992 and last year, according to the U.S. Centers for Disease Control and Prevention. 

Anthrax experts cite different reasons for the declines in the two forms of the disease. 

Inhaled anthrax is nicknamed "Woolsorter's disease," because of cases once seen in factories where workers handled contaminated wool or animal hair. In 1957, four workers at a New Hampshire textile plant died of the disease, ironically during the test of an anthrax vaccine. None of the workers who died had received the vaccine. 

In such settings, bales of wool, when opened, would give off dust, possibly including anthrax germs, said anthrax expert Martin Hugh-Jones of the Louisiana State University School of Veterinary Medicine. 

But federal workplace regulators began to require better ventilation systems in wool and animal hair mills in the 1950s, sharply reducing the risk, he said. 

There are other reasons for the decline. There are far fewer woolen mills today than in the 1950s, offering fewer chances to expose workers. And the few remaining woolen mills in America buy most of their wool from overseas, where it is fully cleaned before it arrives at the plant, said Mike Harris, president of Faribault Woolen Mills in Faribault, Minn. 

The Faribault mill buys only from known sources, and when the wool isn't washed, the mill washes the wool itself, said Brenda Shepherd, plant manager. 

"There's so little dirty wool being touched in America today," Shepherd said. 

Jeff Bender, an anthrax expert at the University of Minnesota College of Veterinary Medicine in St. Paul, said that rather than accepting wool from dead animals, which could have been infected, wool mills now use material taken from live animals. 

As for the drop in the skin form of anthrax, Hugh-Jones notes that these cases typically come from handling livestock with anthrax, and that the incidence of the animal disease has dropped sharply in the United States. So there's less animal disease for people to be exposed to, he said. 

In the 1920s and 1930s, the disease occurred in animals "coast to coast," he said. But the widespread use of an improved animal vaccine beginning in the 1960s greatly reduced that problem, he said. 

Bender also credits the education of ranchers and others about the handling of anthrax-infected animals, to reduce the chance of human infection.