Detection of antibodies against Leptospira serovars via microscopic agglutination tests in dogs in the United States, 2000-2007.

Objective: To use results of microscopic agglutination tests (MATs) conducted at a commercial veterinary diagnostic laboratory to determine temporal and demographic distributions of positive serologic test results for leptospirosis in dogs and identify correlations among results for various Leptospira serovars.

Design: Serosurvey.

Study Population: MAT results for 33,119 canine serum samples submitted to a commercial veterinary diagnostic laboratory from 2000 through 2007.

Procedures: Electronic records of MAT results for dogs were obtained from a veterinary diagnostic laboratory. Seropositivity for antibodies against Leptospira serovars was determined by use of a cutoff titer of >or=1:1,600 to reduce the possible impact of postvaccinal antibodies on results. Correlations between results for all possible pairs of serovars were calculated by ordinal ranking of positive (>or=1:100) antibody titer results.

Results: 2,680 samples (8.1%; 95% confidence interval [CI], 7.8% to 8.4%) were seropositive for antibodies against Leptospira serovars. The highest percentage of positive MAT results was for the year 2007 (10.2%; 95% CI, 9.5% to 10.9%) and for the months of November and December during the study period. Antibodies were most common against serovars Autumnalis, Grippotyphosa, Pomona, and Bratislava. Seroprevalence of leptospirosis was lowest for dogs>10 years of age but was similar across other age strata.

Conclusions And Clinical Relevance: Leptospirosis can affect dogs of small and large breeds and various ages. Although an increase in proportions of positive MAT results was evident in the fall, monthly and annual variations suggested potential exposure in all months. Because of the limitations of MAT results and the limited number of serovars used in the test, bacterial culture should be used to identify infective Leptospira serovars.