Retrospective analysis of Leptospira microscopic agglutination test results identifies Autumnalis as the predominant serovar in the southeastern United States.

Abstract

OBJECTIVE: To carry out a retrospective analysis of Leptospira microscopic agglutination test (MAT) results performed at Tifton Veterinary Diagnostic and Investigational Laboratory in Georgia from June 2015 to December 2023. METHODS: Test records for MAT against 7 Leptospira interrogans serovars (Autumnalis, Bratislava, Canicola, Grippotyphosa, Hardjo, Icterohaemorrhagiae, and Pomona) were retrieved from submissions among cattle, dogs, goats, equids, pigs, and wildlife/exotic species. Further categorization was performed by state and health conditions for seropositive animals, including by breed purpose for cattle (beef, dairy, and dual purpose) and body weight groups for dogs (large, medium, and small). RESULTS: Across all species, the seropositivity rate was 52.3% (552 of 1,055), and the most frequently detected MAT antibodies were against serovar Autumnalis (60.3%; 95% CI, 56.1% to 64.4%), followed by Icterohaemorrhagiae (52.7%; 95% CI, 48.5% to 57.0%). Equids had the highest seropositivity rate (82.5% [47 of 57]) followed by pigs (80.0% [16 of 20]), cattle (54.1% [351 of 649]), dogs (45.6% [131 of 287]), goats (23.3% [7 of 30]), and exotic species (0% [0 of 12]). The highest MAT titer (1:12,800) was detected in a Florida dairy cow against Pomona; a Georgia dog against Autumnalis, Grippotyphosa, and Pomona; and a South Carolina Paint Horse against Pomona. CONCLUSIONS: In the southeastern region of the US, the most frequently detected MAT titers were against serovar Autumnalis in dogs, equids, goats, and pigs, while in cattle, Autumnalis was the second most frequent serovar after Icterohaemorrhagiae. CLINICAL RELEVANCE: The frequent and/or exclusive detection of Autumnalis and Bratislava MAT titers supports the inclusion of these 2 serovars in leptospirosis vaccines and MAT panels used in veterinary diagnostic laboratories across the US.