Prevalence Of Serum Antibodies Against 6 Leptospira Serovars In Healthy Dogs In Michigan¹

Continued urbanization and the increasing contact between suburban pets and various wildlife reservoirs means working breeds are no longer the only dogs at risk from the growing number of Leptospira serovars.

A cross-sectional study conducted by Stokes and Kaneene et al determined the prevalence of antibodies against 6 Leptospira serovars and determined the risk factors associated with positive Leptospira titers in healthy client-owned dogs in Michigan¹.

A structured questionnaire was mailed to 767 private small animal veterinary practices in the lower peninsula of Michigan to solicit participation. The state was divided into 4 geographic regions (Northern, Central, Southeastern and Southwestern) and a proportional random sample of 150 practices was selected to ensure that the number of practices in the study would be proportional to the actual number of practices found in each of the 4 geographic regions. Participating practices were asked to submit serum samples from up to 20 healthy client-owned dogs between August and December 1999, when the highest antibody concentrations in dogs exposed to Leptospira species would be expected to occur.

Only dogs judged as healthy on the basis of results of a physical examination and history were candidates for the study. Samples were acquired while veterinarians were collecting blood for clinical diagnostic tests (eg, routine preanesthetic testing). Dogs with a history of leptospirosis or current liver, renal, or other systemic disease were excluded from the study. Because maternal antibodies could interfere with interpretation of the results, all participants were at least 4 months of age.

One-thousand-two-hundred and forty-one dogs of at least 4 months of age were examined by veterinarians at private practices. Vaccinated and unvaccinated dogs were enrolled in the study, which occurred prior to the availability of a 4-serovar (L. canicola, L. grippotyphosa, L. icterohaemorrhagiae, and L. pomona) Leptospira vaccine. Sera were tested by use of the MAT to determine antibody titers against Leptospira serovars L. bratislava, L. canicola, L. grippotyphosa, L. hardjo, L. icterohaemorrhagiae, and L. pomona. A questionnaire was used to collect demographic information about each dog to identify risk factors associated with seropositive status.

Three-hundred and nine of 1,241 (24.9%) dogs had antibody titers against at least one of the 6 Leptospira serovars, which suggested exposure to Leptospira spp. Prevalence of antibodies was highest to serovars L. grippotyphosa, followed by L. bratislava, L. canicola, L. icterohaemorrhagiae, and L. pomona.

The serovars most frequently associated with likely exposure of seropositive dogs, L. bratislava and L. grippotyphosa, were serovars that were not present in canine vaccines during the study period.

No significant associations were found between likely exposure to Leptospira spp. and breed. Although the associations were not significant, the breed groups with the highest likelihood of exposure were terriers for all serovars and serovars L. bratislava and L. icterohaemorrhagiae, toy breeds for serovar L. canicola, and working breeds for L. grippotyphosa and L. pomona (Table 1).

Among healthy dogs from the lower peninsula of Michigan, >20% have antibodies against Leptospira serovars historically considered uncommon but more recently incriminated as causing clinical canine leptospirosis.

Wildlife and livestock may be of increasing importance as reservoirs for canine leptospirosis as urbanization continues to occur. Administration of a vaccine containing Leptospira serovar L. grippotyphosa (like the Vanguard 4-Way Leptospira vaccines from Pfizer Animal Health) and limiting exposure to wildlife reservoirs may be appropriate considerations to help mitigate these trends.