Effects of recent Leptospira vaccination on whole blood real-time PCR testing in healthy client-owned dogs

Abstract

Background: Bacterin-based canine Leptospira vaccines could present a challenge for the use of whole blood real-time polymerase chain reaction (PCR) as a diagnostic tool. Recent vaccination could induce positive results if the targeted DNA fragment is present within the vaccine and in the blood of the recently vaccinated dog. Objectives: The objective of this study was to assess whether 2 available 4-serovar vaccines induce a positive real-time PCR reaction in the blood of healthy recently vaccinated dogs. Animals: Twenty healthy dogs. Methods: This was a prospective study. Dogs were assigned to 1 of 2 vaccine groups. Both vaccines were culture-based and include Leptospira interrogans serovars Pomona, Canicola, and Icterohaemorrhagiae and Leptospira kirschneri serovar Grippotyphosa. Whole blood for real-time PCR and serum for the microscopic agglutination test (MAT) were collected prior to and 3 and 7 days after vaccination and weekly thereafter for 8 weeks. Two real-time PCR tests targeting 2 different genes were performed independently in a blinded fashion. Results: Both Leptospira vaccines produced positive real-time PCR reactions when assayed undiluted or diluted 1:100 in canine blood. However, blood samples drawn from all dogs at all time points after vaccination were negative on PCR. All dogs developed MAT titers. Conclusions and Clinical Importance: Recent vaccination with 2 commercially available vaccines does not interfere with the use of real-time PCR for the identification of acute Leptospira infection in dogs. © 2011 by the American College of Veterinary Internal Medicine.