Leptospirosis is a contagious and potentially life-threatening bacterial infection of dogs caused by various strains of a spiral-shaped microorganism called Leptospira interrogans. Domestic cats are rarely found to be ill with this disease. Previously, routine vaccination against the two most common strains had practically eradicated the disease in dogs. By the 1990’s, however, the disease had reemerged with different strains of the bacteria affecting dogs. The resurgence of this infection is probably due to changes in the disease transmission associated with increased direct and indirect contact opportunities with wildlife, even in urban and suburban areas.

Leptospirosis occurs naturally in a wide range of wildlife species including rats, mice, voles, raccoons, foxes, opossums, skunks, deer, moose, squirrels, woodchucks and weasels. Domestic animals including swine, cattle, horses and dogs may become infected and transmit the disease. Humans are also at risk for infection.

Leptospirosis is transmitted between animals by direct or indirect contact. Direct transmission of the disease includes contact with infected urine, venereal and placental transfer, bite wounds or ingestion of infected tissue. Indirect transmission of the disease involves contact with water sources, soil, food or bedding usually contaminated by urine from an infected animal. Some animals act as asymptomatic carriers and shed bacteria in their urine; others become ill and die.

Canine leptospirosis is widespread in the United States and it occurs more commonly in spring and early fall when the wet soil conditions and moderate temperatures allow the organism to survive in the environment for many months. Stagnant or slow-moving water is a near ideal habitat for the organism. Periods of high rainfall will often be associated with increased infection.

Affected dogs can remain apparently healthy and shed leptospires in their urine, increasing the risk of transmission to other dogs or to humans. Some of these dogs later develop progressive chronic kidney disease or chronic liver disease.

Dogs with acute leptospirosis may show fever, muscle pain or stiff gait, weakness, conjunctivitis, vomiting or loss of appetite within 4 to 12 days of exposure. Following the onset of these nonspecific symptoms, some dogs develop severe kidney failure and in some cases severe liver failure. These dogs are very ill and may have decreased (or rarely increased) urine production, discolored (orange) urine, malodorous breath, vomiting and diarrhea, breathing difficulties, bleeding tendencies or jaundice. Severely affected dogs (especially puppies) can progress rapidly to death if not treated.

Early recognition and treatment are important to avoid rapid deterioration and life-threatening complications. Suspicion is initially based on learning that your pet has had possible wildlife exposure, suggestive symptoms, and the presence of acute kidney or liver failure. The diagnosis is confirmed by blood and urine tests and by the presence of antibodies against Leptospira in the blood. In some situations, laboratory tests may need to be repeated two to four weeks after the onset of symptoms in order to confirm the diagnosis. Until the infection is confirmed, precautionary measures to avoid transmission to other dogs and to humans should be taken. Any dog suspected of having leptospirosis should be treated promptly.

Early and appropriate antibiotic therapy with intravenous fluid therapy is essential in order to shorten the duration of disease and decrease the severity of kidney and liver damage. Most dogs need intensive care treatment. Additional medications other than antibiotics may be required to ensure survival.

The prognosis depends on the severity of the infection at the time of diagnosis and on the level of care that can be provided. Even in severe cases, the prognosis is good providing advanced kidney or liver failure is not present. Most adult dogs (80-90%) will leave the hospital with mild to moderate impairment of kidney function that will normalize over the following weeks to months. The prognosis is considerably worse in puppies as liver or kidney damage tends to be much more severe.

Other dogs living with a known infected dog should be given appropriate antibiotic treatment. Yearly or twice yearly vaccination in high-risk environments is recommended. Vaccination sometimes causes mild reactions (fever, decreased appetite, allergic reactions), but the benefit of protecting against this potentially life-threatening infection seems to outweigh the risks of the side effects.

Leptospirosis can also be transmitted to humans through direct and indirect contact with infected animals (particularly contaminated urine). Leptospirosis is considered the most common infectious disease transmitted from animals to humans worldwide. Manifestation of the disease in humans varies from mild flu-like symptoms with fever to signs of severe liver, brain, kidney and lung damage. Owners of a known infected dog should be aware of this risk, especially if exposure to urine or contaminated soil or water has occurred, and should consult their physician about the need to take any particular precautions.

For more information on this subject, speak to the veterinarian who is treating your pet.