Feline leptospirosis

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Dogs are considered the normal reservoir host for Leptospira serovar canicola. Based on studies that focused on urban populations of dogs, serovars canicola and icterohemorrhagiae were considered the most prevalent serovars infecting dogs. Studies that have included more rural and suburban populations of dogs document the predominance of serovars of grippotyphosa and pomona as causative agents of canine leptospirosis. Other serovars, particularly bratislava, have also been implicated. A variety of factors, such as increased exposure to raccoons and opossums in suburban and rural areas, communities encroaching on wildlife habitats, and poor farming practices, may explain the rise of previously low-prevalence serovars. Rodents continue to play an important role as reservoirs in urban settings.

Clinical Findings

There is no age or gender predilection, although German Shepherds may be at increased risk compared with other breeds. The incubation period is 4-12 days but may be as short as 2 days. Acute renal failure occurs in 80-90% of dogs that develop clinically significant disease. Early findings are nonspecific and include fever, depression, lethargy, anorexia, arthralgia or myalgia, and oculonasal discharge. This may progress within a few days to a uremic crisis characterized by vomiting, dehydration, lumbar pain from renomegaly and nephritis, and tongue-tip ulceration and necrosis. Icterus and bilirubinuria, suggestive of cholestasis and/or hepatic necrosis, develop in ~20% of these cases and may be present without renal failure. In dogs that develop milder forms of renal failure, polyuria and polydipsia may be the primary sign. Other syndromes reported in dogs include intussusception, pulmonary haemorrhage, uveitis, pneumonitis, chronic hepatitis, and reproductive failure.

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 anaemia 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 haemorrhage 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. Pyuria is less frequently seen, and glycosuria may be identified on occasion as a result of renal tubular damage.

Lesions

Gross findings can include petechial or ecchymotic haemorrhages 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.

Diagnosis

Serology is the most useful and frequently used diagnostic test for dogs. Acute and convalescent titres may be necessary to confirm a diagnosis. Other diagnostic tests, such as darkfield microscopy, fluorescent antibody, PCR, culture, and histopathology are less frequently used antemortem. Demonstration of leptospires in tissues with silver staining or fluorescent antibody testing are preferred post-mortem.

Treatment

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 consists of sodium penicillin G, ampicillin, or doxycycline to eliminate leptospiremia, followed by doxycycline to eliminate the renal carrier phase. The fluoroquinolone antibiotics such as enrofloxacin also appear to be leptospirocidal. Doxycycline is preferred over tetracycline, particularly in azotemic patients. First-generation cephalosporins are not effective at any stage of the disease. Previously described regimens of IM procaine penicillin G and dihydrostreptomycin should not be used.

Prevention

Commercial bacterins for dogs are available for serovars canicola, icterohaemorrhagiae, grippotyphosa, and pomona. There does not appear to be good cross-immunity between serovars, and vaccinated dogs may still be susceptible to infections with other serovars. Vaccination is recommended at yearly intervals but may be needed more frequently in enzootic areas. Dogs that have recently been exposed to leptospirosis may be treated prophylactically with oral amoxicillin or doxycycline for 7-10 days to prevent infection.