Dogs are the maintenance host for serovar canicola, and prior to widespread vaccination programs, serovars canicola and icterohaemorrhagiae were the most common serovars in dogs in the USA. The prevalence of canine serovars has shifted significantly in the last 15 years; currently the most prevalent serovars are grippotyphosa, pomona, and bratislava—with the relative proportion of these serovars differing geographically. Serovar canicola still circulates in the canine population, particularly in stray dogs. Serovar icterohaemorrhagiae is most commonly identified in dogs with exposure to rats and particularly in urban areas. Detection of antibody reactive with serovar autumnalis in dog sera in the USA and Canada has prompted speculation that this organism is causing disease. However, serovar autumnalis has not been isolated from dogs in the USA or Canada, and there is evidence that use of vaccines containing serovars grippotyphosa and pomona can induce high titers of cross-reacting antibody against serovar autumnalis. Therefore, the role of serovar autumnalis in canine disease awaits microbiologic evidence.

The incubation period is usually 4–12 days. There are relatively minor clinically relevant differences in disease produced by the common serovars. There is significant variation in pathogenicity among isolates within a serovar. Therefore, dogs with leptospirosis can be expected to exhibit a spectrum of clinical signs confounding clinical diagnosis. Early clinical signs are nonspecific and may include depression, lethargy, anorexia, vomiting, diarrhea, conjunctivitis, fever, and arthralgia or myalgia. Hours to days later, specific signs of renal and/or hepatic disease are observed, with mild to moderate elevations in BUN, creatinine, and bilirubin to profound jaundice, oliguric renal failure, hyperphosphatemia, thrombocytopenia, and death. Less commonly, uveitis, pancreatitis, pulmonary hemorrhage, and chronic hepatitis are recognized.

The most common hematologic abnormality is a mild to moderate neutrophilic leukocytosis without a left shift, although a normal WBC count may be seen. A mild anemia is seen in 25–35% of cases, often as a result of subclinical hemolysis. Thrombocytopenia occurs in only 10–20% of dogs but is rarely severe enough to be a source of bleeding. Vasculitis is typically the cause of hemorrhage associated with leptospirosis. Azotemia is the most common finding on a serum biochemistry profile. When liver values are abnormal, elevations in serum alkaline phosphatase are typically more pronounced than elevations in ALT and AST. Serum bilirubin is elevated in ~20% of cases. Isosthenuria or hyposthenuria is typically present on the urinalysis, and hematuria, proteinuria, and granular casts are identified in ~30% of cases.

Gross findings can include petechial or ecchymotic hemorrhages on any organ, pleural, or peritoneal surface; hepatomegaly; and renomegaly. The liver is often friable with an accentuated lobular pattern and may have a yellowish brown discoloration. The kidneys may have white foci on the subcapsular surface. Microscopic findings in the liver may include hepatocytic necrosis, nonsuppurative hepatitis, and intrahepatic bile stasis, while swollen tubular epithelial cells, tubular necrosis, and a mixed inflammatory reaction may be seen in the kidneys. Chronic hepatitis and chronic interstitial nephritis are described in less severe cases.

Serology is the most frequently used diagnostic test for dogs. Acute and convalescent titers may be necessary to confirm a diagnosis. Other diagnostic tests such as immunofluorescence, PCR, and culture are useful, but collection of samples prior to the administration of antibiotics should be considered for maximal sensitivity.

Renal failure and liver disease are treated with fluid therapy and other supportive measures to maintain normal fluid, electrolyte, and acid-base balance. Antibiotic therapy is indicated. Systemic treatment with penicillin or its derivatives is particularly useful in acutely ill dogs. These drugs are indicated for eliminating leptospiremia. If the disease is mild and the dog will tolerate oral therapy, doxycycline or fluoroquinolones may be used. Primary therapy should be followed by a 2- to 4-wk course of doxycycline to eliminate organisms from the kidney and decrease shedding. First- and second-generation cephalosporins are not recommended. Dogs that have recently been exposed to leptospirosis may be treated prophylactically with oral amoxicillin or doxycycline for 7–10 days to prevent infection.

Commercial bacterins for dogs are available for serovars Canicola, Ic-terohaemorrhagiae, Grippotyphosa, and Pomona. Vaccinated dogs may still be susceptible to infection with other serovars. In general, the vaccines provide good protection from clinical disease but may not protect all dogs from infection or renal shedding. Concerns exist regarding hypersensitivity reactions following leptospiral vaccination in dogs. These reactions are rarely life-threatening and are managed medically. Vaccination is recommended at yearly intervals but may be needed more frequently in enzootic areas.

Last full review/revision March 2012 by Carole Bolin, DVM, PhD