Leptospirosis is a disease caused by antigenically distinct members of the genus of bacteria known as Leptospira. Leptospirosis affects virtually all mammals, and symptoms vary in severity from asymptomatic to fatal, depending on the host involved and the infective serological group (serovar). Leptospira organisms are small, filamentous, and motile, ranging in size from 0.1 to 0.3 µm in width and 6 to 20 µm in length. They are easily killed by disinfectants, heat, drying, and pH values below 6 or above 8 (Michigan, 2010).

Although more than 250 serovars of pathogenic Leptospira are recognized, a subset of serovars are prevalent within a particular region or ecosystem and are associated with one or more maintenance hosts which serve as reservoirs of infection. Maintenance hosts are often wildlife species and sometimes domestic animals and livestock. Each serovar typically behaves differently within its maintenance host species than it does in other, incidental host species (Merck Veterinary Manual).

Leptospirosis has a cosmopolitan distribution, and can be found in domestic and wild animals across the U.S. and worldwide (Michigan, 2010).

Leptospirosis can affect nearly all mammals, including domestic animals, wildlife, and humans. Wildlife species most commonly infected include rodents, beaver, deer, and raccoons (Stitt, 2011); however, leptospirosis usually has little to no effect on the health of wildlife. Cattle, swine, dogs, and horses are the most commonly affected domestic animals.

Leptospira are ubiquitous and abundant due to their abilities to infect a variety of animals and to persist outside the host. Transmission usually occurs through contact with contaminated water or food, or through transplacental transmission in an infected dam. The bacteria have a predilection for the kidneys and the urinary tract where they may produce a persistent infection. The organisms may be excreted with the urine into the environment. Infective urine constitutes the major source of infection for humans, domestic animals, and wild animals. The route of transmission is usually through ingestion of the bacteria or by direct contact of mucous membranes (eye, nose, mouth) or abraded skin with infected urine droplets or urine-contaminated water. Transmission may also occur through ingestion of infected carcasses by carnivorous species. Leptospira can survive outside the body of the host for several weeks if environmental conditions are favorable. The bacteria prefer moist, slightly alkaline soil, stagnant ponds, and low-flow, slow-moving, slightly alkaline streams.

Once infection has occurred, Leptospira multiply in the kidneys, lungs, reproductive organs and brain. Uterine penetration of pregnant animals results in infection of the fetuses (Western, 2009; Michigan, 2010).

Clinical signs observed with leptospirosis vary from unapparent to fatal depending on the host and the serovar. Subclinical disease is common in maintenance hosts, but severe disease may develop in incidental hosts. In humans the disease is characterized by fever, headaches, muscle aches, vomiting, conjunctivitis, weakness, meningitis, and in severe cases, icterus (jaundice seen in the sclera of the eye), and kidney failure. In domestic species clinical signs vary considerably by species, but may consist of fever, weight loss, anorexia (loss of appetite), uveitis, pancreatitis, abnormal milk secretion, anemia, hematuria (blood in the urine), hemoglobinuria (hemoglobin in the urine), muscular weakness, pulmonary congestion, and icterus.

In both maintenance hosts and incidental hosts, infection during pregnancy may result in abortion, stillbirths, weak neonates, or normal births. Naturally occurring Leptospira infection in wildlife are often mild and self-limiting with the host recovering from the initial stages of the disease while remaining as a reservoir host. However, experimental infections in white-tailed deer resulted in clinical signs ranging from an unapparent infection to a febrile response, abortion, and death. Clinical signs observed in experimental deer included transient fever, anorexia, weakness, anemia, hemoglobinuria and icterus (Michigan, 2010).

Leptospirosis is considered one of the most widespread zoonotic diseases in the world. There are about 100-200 human cases a year in the US (Western, 2009). People can become infected through contact with urine or tissues of infected animals, with water, soil, or vegetation contaminated by infected urine, or by the consumption of food or drinking water contaminated by infected urine. The diseases can be fatal if not treatedpromptly, but can be successfully treated with antibiotics. Disease in humans ranges from mild to severe. Symptoms may include fever, headache, chills, depressed appetite, red urine, depression, abdominal pain, muscle aches, vomiting, jaundice, red eyes, diarrhea, and/or rash.

Wildlife professionals, trappers and hunters can take preventative measures to avoid exposure and infection. Wear gloves and wash hands well when handling any wild animal, but especially rodents, beavers, and raccoons. Clean cuts or wounds with soap and water. Wear boots or waders when wading in water, and avoid direct contact with water potentially contaminated by animal urine (Stitt, 2011; Western, 2009). No human cases of leptospirosis have been traced to contact with deer, and the risk of infection from free-ranging, wild animals is very low (Michigan, 2010). However, leptospirosis is also a potential hazard to people who work with domestic livestock or who enjoy outdoor recreation such as swimming and kayaking.

Michigan Wildlife Disease Manual. 2010. Michigan Department of Natural Resources. Website

Stitt, Tyler. 2011. Diseases You Can Get From Wildlife - A Field-guide for Hunters, Trappers, Anglers and Biologists. British Columbia Ministry of the Environment.

Western Wildlife Disease Workshop Notebook. 2009. Southeastern Cooperative Wildlife Disease Study. College of Veterinary Medicine, University of Georgia.