Leptospirosis: Mild Winters Could Mean More Cases

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.


Leptospira interrogans

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.

Hunting dogs that retrieve game from water and people who swim in contaminated water have historically been at high risk of acquiring lepto. In 1998, for example, several participants in a triathlon in Springfield, Ill., contracted leptospirosis after swimming in a contaminated lake.

Recently urban sprawl has contributed to a rising incidence of lepto infections. Housing developments are built closer to wild areas, and thus closer to the wildlife that can carry lepto. Pets no longer have to go to remote ponds to drink contaminated water; the retention pond in their local subdivision may be contaminated with lepto from wild animals' urine.

Lepto is most often acquired through oral ingestion, but it can also enter the body through open wounds, abrasions, or mucus membranes in the eye or nose. Maddox notes, "It takes only a small number of organisms to infect and cause disease."

Leptospira can infect the blood and spread to the lymph nodes, liver, and kidneys. Signs of lepto mimic signs of many other diseases, and include fever, lethargy, gastrointestinal upset, and loss of appetite. Owners of small animals should consult a veterinarian whenever their pet displays signs of liver trouble, such as jaundice (yellowing of the eyes, skin, or gums) or yellow foamy vomit, or signs of kidney problems, such as increased urination, dark or bloody urine, or unusual "accidents" in the house.

Since leptospirosis can lead to liver or kidney failure if left untreated, accurate diagnosis is crucial. Veterinarians can quickly identify Leptospira during acute infection by sending urine, liver, or kidney biopsies to a diagnostic laboratory for an inexpensive qPCR test, a type of DNA detection. Blood tests usually can't detect lepto antibodies until two to three weeks after infection and might be a better indicator of a longstanding or chronic disease.

Antibiotic treatment for lepto is effective if the disease is caught early, but, of course, prevention is the best medicine. Make sure dogs do not drink out of puddles or ponds outdoors; bring tap water for your dog or horse when you take them on long outings. Always keep wild animals away from barns, food, and water supplies to prevent lepto and other diseases. For dogs, vaccination might also be advised by your veterinarian.

Cats and many dogs can carry the bacteria without developing disease, so they can spread the disease without owners knowing. Since lepto can make humans ill, household sanitation is important. Pet owners should always wash their hands after touching their pet and cleaning household "accidents" and litter boxes. People who camp should also protect themselves by filtering, boiling, or treating lake or stream water before drinking it.

For more information about leptospirosis, contact your local veterinarian.

An archive of Pet Columns from the University of Illinois College of Veterinary Medicine is available online at www.cvm.uiuc.edu/petcolumns. Requests for reprints of this article may be directed to Mandy Barth, mandyb@uiuc.edu.  

About the Author

Sarah Dowling

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