Canine leptospirosis is a common infectious disease of dogs in tropical countries as Brazil. To confirm the diagnosis of leptospiral infection, serum microscopic agglutination test (MAT) is recommended. Interpretation of the results is difficult, mainly in previous vaccinated dogs.
To evaluate the usefulness of PCR as a tool for diagnosis.
Twenty-four dogs, presenting signs of acute leptospirosis, were studied. Serum samples were submitted to MAT test as recommended (WHO). Urine samples obtained by cystocentesis were cultured in Fletcher medium at 28–30°C for up to two months, in an attempt to isolate the organism involved. Additionally, conventional PCR (Merien 1992) was done on urine samples.
At first presentation, six dogs were negative for MAT test while ten dogs presented anti-leptospiral antibodies for at least one serovar in titer < 800 and the remaining eight dogs showed titer > 800. Because of the history of previous vaccination, only the latter were considered as significant titer. When paired serum samples were obtained, four of six dogs initially negative on MAT, showed serum conversion, thus confirming the diagnosis of leptospirosis. As to PCR, genetic material of Leptospira spp. was found on eleven dogs, and organism isolation was successfully obtained from three of these dogs. No association between MAT and PCR was observed (Fisher's exact test).
Despite the low sensitivity observed, PCR can be used in combination with serologic tests to improve the sensitivity of diagnosis of leptospirosis.