Anthrax is a potentially deadly bacterial infection, which is extremely rare.
Its spores live in the soil for years and it most commonly occurs in cattle, sheep and goats, but can also infect humans.
It was once fairly common in Britain and Ireland among workers coming into contact with infected hides or fleeces, before ways were devised of treating the skins chemically to kill the spores.
The most common form in humans is cutaneous anthrax, affecting the skin - as has now occurred in NBC in New York.
Pulmonary anthrax - as occurred in Florida - affects the lungs.
Animals can become infected by grazing on it on contaminated land.
People may become infected via a scratch or sore if they handle materials from infected animals.
Pulmonary anthrax occurs as a result of inhaling large numbers of spores contained in infected animal fibres.
It can be caught internally if swallowed, causing ulcers in the intestine and stomach and gangrene of the spleen.
Pulmonary anthrax causes severe breathing difficulty and is mostly fatal within three days.
In cutaneous anthrax, an itchy area develops at the site of entry of the spores, which becomes a large blister, then a black scab, with swelling of the surrounding tissues.
It is treatable with large doses of penicillin in its early phases.
Without treatment, the infection may spread to lymph nodes and the bloodstream, and may be fatal.
Although it is extremely rare in the developed world, serious epidemics have occurred in some developing countries.
Because anthrax could be used in biological warfare, military personnel are vaccinated.