Several years of mild winters in the Midwest might bring veterinarians and physicians more than the usual number of cases of leptospirosis, or "lepto," a bacterial disease that can affect cattle, swine, horses, wildlife, dogs, and humans.

According to Carol Maddox, MS, PhD, a microbiologist at the University of Illinois College of Veterinary Medicine in Urbana, Ill., several strains of the bacterium Leptospira interrogans survive in water and can persist in the natural environment in lakes, streams, and retention ponds.

In the spring the bacteria are ingested by raccoons, opossums, and other wildlife. While these animals may not get sick from lepto, they act as hosts for the disease, enabling the bacteria to multiply. The bacteria are spread through the animals’ urine during spring and summer. Then pets and people come into contact with contaminated water, and cases of the disease usually peak in the fall.

Normally, Leptospira numbers dwindle during cold winters, keeping the disease in check. However, Maddox predicts that places like the College’s Veterinary Teaching Hospital could see a heavier caseload, starting sooner than usual, since many lepto organisms probably survived the recent mild winters