Disease Overview

Leptospirosis is an infectious disease that causes serious illness in dogs, other animals, and people. The disease is caused by spiral-shaped bacteria called leptospires that live in water or warm, wet soil. Leptospirosis causes a variety of signs, including fever, lethargy, and lack of appetite, but it can develop into a more severe, life-threatening illness that affects the kidneys, liver, brain, lungs, and heart.

Merck Animal Health Solutions

For Leptospirosis


Transmission of leptospirosis can occur through direct contact or indirectly through environmental exposure. Leptospires commonly enter the body through mucous membranes in the mouth, eyes, or nose or through abraded or water-softened skin.25,26

Leptospira first multiply in a host animal’s bloodstream, then move on to the kidneys and other tissues to continue reproducing. Leptospires pass from the kidneys into the urine and then are shed back into the environment, where they can infect other animals or people.

Clinical Signs27

  • Fever
  • Lethargy
  • Weight loss
  • Anorexia
  • Depression
  • Acute renal failure

Risk Factors

  • Dogs likely to explore the outdoors (even dogs in fenced yards may be exposed to infected urine from wildlife or rodents)25,28
  • Working dogs, especially hunting and herding breeds25
  • Dogs with access to ponds, lakes, streams, or standing water25
  • Dogs in crowded shelters or other pet care facilities25
  • Urban dogs that exercise outdoors and may come in contact with rodent urine or rodent-contaminated fomites25


25. Greene CE, Sykes JE, Brown CA, Hartmann K. Leptospirosis. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. 3rd ed. St. Louis, MO: Saunders/Elsevier; 2006:402−417.
26. Center for Food Security and Public Health, Iowa State University. Leptospirosis. Available at: http://www.cfsph.iastate.edu/Factsheets/pdfs/leptospirosis.pdf. Accessed December 28, 2010.
27. Kahn CM, Line S, eds. Leptospirosis. In: The Merck Veterinary Manual. 9th ed. Whitehouse Station, NJ: Merck & Co., Inc.; 2005:525−529.
28. McDonough PL. Leptospirosis in dogs: current status. In: Carmichael L, ed. Recent Advances in Canine Infectious Diseases. Ithaca, NY: International Veterinary Information Service; 2001. Available at: http://www.ivis.org/advances/Infect_Dis_Carmichael/mcdonough/ivis.pdf. Accessed December 28, 2010.