Leptospirosis is caused by a bacterium that is widely distributed among animal populations in the United States. Infection of man results from contact with a diseased animal or from contaminated water or soil. Domestic animals (cattle, hogs, dogs) as well as wild animals (foxes, squirrels, skunks, rats) can harbor the infection. The bacteria usually gain entry into the body through a break in the skin, but sometimes may do so through the mouth or eyes. Farmers, abattoir workers, hunters, or children who have been swimming in contaminated ponds are most often affected.

The incubation period of seven to fourteen days is followed by the abrupt onset of symptoms-headache with fever, chills, nausea and vomiting and muscle aches. The illness lasts about 2 weeks, remits for a few days, then recurs for another two to four days. The disease may be accompanied by a rash, neck stiffness, yellow jaundice, and bleeding tendencies.

Most of those who develop leptospirosis recover, though the mortality rate may be high if jaundice sets in. Antibiotics may be useful if given early in the illness.