Leptospirosis is a disease of humans and domestic and wild animals caused by the bacteria Leptospira interrogans. There are several distinct subtypes of L. interrogans that cause varying degrees of disease severity depending on the species that becomes infected.
Leptospirosis is a zoonotic disease, which means that humans can get the disease from infected domestic or wild animals, and it is potentially fatal. Leptospirosis is reemerging and the incidence in people and animals is increasing worldwide. People usually become infected by coming in contact with animal urine containing the bacteria, or by swimming in contaminated bodies of water. People who work outdoors, work with animals, or participate in outdoor recreational activities have an increased risk of contracting leptospirosis.
Leptospirosis can potentially occur in all mammalian species. Domestic animals including but not limited to cattle, pigs, horses, and dogs can become infected. Leptospirosis has been demonstrated in many wildlife species such as rodents, white-tailed deer, raccoons, foxes, skunks, and California sea lions.
Leptospirosis is distributed worldwide, but occurs more commonly in temperate and tropical climates because the bacteria require warmth and moisture to survive. L. interrogans is killed by disinfectants, drying, heat, or pH above 8 or below 6, but it can survive outside of the host under certain environmental conditions. The bacteria prefer slightly alkaline soils and stagnant or slow moving water. Human infections usually occur in summer and early fall. Leptospirosis is diagnosed sporadically in Pennsylvania.
L. interrogans preferentially colonizes the kidney and is excreted in the urine of infected animals. Leptospirosis is usually transmitted to animals and humans via exposure of the mouth, eye, nose, or damaged skin to urine containing the bacteria. The bacteria can cross intact, wet skin as well. The disease can also be transmitted via contaminated food or water, during mating, or across the placenta in pregnant animals. Wild carnivores often acquire the disease by consuming infected carcasses. The bacteria can survive for weeks to months outside of the host in favorable environmental conditions, so the disease can be transmitted indirectly without any interaction with an infected animal.
The severity of clinical signs varies widely depending on the host species and the subtype of L. interrogans involved. At times the infection is completely asymptomatic even though bacteria are being shed in the urine. Other times the disease can be quite severe resulting in fever, loss of appetite, depression, dehydration, vomiting, abdominal pain, and death. The bacteria have a predilection for the kidneys, lungs, reproductive organs, and brain, so infection can result in renal failure, pneumonia, and meningitis. Infected animals may have jaundice and blood in their urine and milk. If the bacteria cross the placenta of a pregnant animal, the fetus can become infected which usually leads to abortion or stillbirth.
It is often challenging to definitively diagnose leptospirosis. Antibody titers can be misleading, and it is difficult to culture L. interrogans from blood or urine. The organism may be isolated from body fluids using special microscopic techniques or laboratory tests.
Although wildlife species are rarely observed showing clinical signs of leptospirosis, they can still shed the bacteria in their urine, which can then infect domestic animals and humans. It is unlikely that leptospirosis will be eradicated from wildlife populations because there are so many different subtypes that can infect many different hosts, and there is evidence that the bacteria is still evolving. As is often the case, prevention is key. For example, people should try to avoid contact with animal urine and should avoid swimming in stagnant or slow moving bodies of water. Hunters, trappers, and people that work outside or with wild or domestic animals should be aware of the risk of exposure to this bacteria and should take precautions including wearing gloves and protective clothing as well as practicing good hygiene.
Centers for Disease Control and Prevention (CDC). 2011. Leptospirosis. http://www.cdc.gov/leptospirosis/index.html.
Leighton, F. A., and T. Kuiken. 2001. Leptospirosis. Pages 498-502. in E. S. Williams and I. K. Barker, editors. Infectious diseases of wild mammals. Iowa State University Press, Ames, Iowa, USA.
Michigan Department of Natural Resources. Wildlife Disease. Leptospirosis. http://www.michigan.gov/dnr/0,1607,7-153-10370_12150_12220-26943--,00.html.
Tilley, L. P., and F. W. K. Smith, Jr. 2007. Blackwell's five-minute veterinary consult: canine and feline. Fourth edition. Blackwell publishing, Ames, Iowa, USA.