Canine leptospirosis is caused by an order of bacteria called spirochetes – slender, spirally undulating bacteria. There are at least four species of the leptospira bacteria (or serovars) that can infect dogs: canicola, icterohemorrhagiae, grippotyphosa, and pomona.
Leptospira are found in wild and domestic animals. The bacteria are spread in the urine, often making their way into water sources and remaining infective in the soil for up to six months. Rats, pigs, raccoons, cattle, skunks, and opossums appear to be the primary reservoirs. With housing spreading into the suburbs, more wildlife are coming into contact with pet dogs. This may be the cause of the upswing in leptospirosis cases. Spirochetes enter a dog’s system through a break in the skin or when the dog drinks contaminated water. Dogs who spend a lot of time in the water are at increased risk, as are dogs who drink out of puddles and dogs who spend time in yards that get a lot of runoff or stay wet after it rains.
Most infections are mild and do not show clinical signs. Signs appear 4 to 12 days after exposure. Fever is present in the early stage. Other signs are loss of appetite for several days, vomiting, lethargy, depression, muscle pain, and sometimes diarrhea or blood in the urine. Leptospirosis primarily affects the kidneys and/or the liver.
In severe cases, the whites of the dog’s eyes turn yellow (jaundice). This indicates hepatitis with destruction of liver cells. Coagulation problems can ensue, with spontaneous bleeding from the mouth and blood in the stools. Following recovery, untreated dogs can become carriers and shed bacteria in their urine for up to a year.
The canicola and gripotyphosa serovars tend to cause kidney damage, and the pomona and icterohemorrhagiae serovars most often affect the liver. Young dogs tend to show liver damage with all of the serovars.
The diagnosis can be suspected based on the dog’s clinical signs. Tests of kidney and liver function will be abnormal. Spirochetes can be detected in the urine and blood by fluorescent antibody staining. Blood tests are available to confirm the diagnosis.
Treatment: Severely ill dogs should be hospitalized for public health reasons and to provide more intensive care. Antibiotic combinations of penicillin and streptomycin are effective against the disease, although doxycycline is now routinely used as well. Enrofloxacin and ciprofloxacin are also sometimes used. Supportive measures include controlling vomiting and diarrhea, correcting dehydration with intravenous fluids, and maintaining nutrition.
Prevention: There is a vaccine for leptospirosis.
Public health considerations: Humans can acquire leptospirosis, generally through the same types of exposures that cause the disease in dogs, such as infected water. It can also spread via contact with infected urine, so precautions should be taken if the family dog has leptospirosis. An infected dog who is asymptomatic can still spread the infection.