Seroprevalence of equine leptospirosis in Connecticut, US

Authors: HAMOND, CAMILA - University Of Connecticut; KANGAS, CANDACE - University Of Connecticut; LEE, VIVIANNE - University Of Connecticut; FANFAN, ANAYAH - University Of Connecticut; Nally, Jarlath; MCGINNIS, HOLLY - University Of Connecticut; SIMS, MAUREEN - University Of Connecticut; RISATTI, GUILLERMO - University Of Connecticut; WUNDER, ELSIO - University Of Connecticut

Submitted to: BMC Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2026
Publication Date: 8/1/2026
Citation: Hamond, C., Kangas, C.L., Lee, V.W., Fanfan, A., Nally, J.E., McGinnis, H., Sims, M., Risatti, G.R., Wunder, E.A. 2026. Seroprevalence of equine leptospirosis in Connecticut, US. BMC Veterinary Research. https://doi.org/10.1186/s12917-026-05749-5.
DOI: https://doi.org/10.1186/s12917-026-05749-5

Interpretive Summary: Animal leptospirosis is caused by spirochete bacteria in the genus Leptospira, which includes more than 40 pathogenic species and over 20 serogroups comprising more than 250 serovars. Disease in animals is prevented by using bacterin vaccines which contain the serovar associated with infection. In the United States, the only equine vaccine for leptospirosis includes serogroup Pomona. Therefore, a seroprevalence study was performed with 397 equine sera to determine which other serovars they may be exposed to. The serogroups most reactive with equine sera were Iquitos, Djasiman, Grippotyphosa, Australis, Pomona, and serovar Room22 strain GWTS1. Results demonstrate a high seroprevalence of equine leptospirosis and strong evidence that horses were potentially exposed to serogroups/serovars not included in commercial bacterin vaccines. Further studies to attempt isolation and genotyping of the pathogen from horses are necessary to better understand the role of horses in the epidemiology of leptospirosis. This information will support diagnostic strategies, vaccine recommendations, risk assessment, and public health actions that can reduce spillover transmission and the impact of this important zoonotic disease.

Technical Abstract: Leptospirosis is a geographically widespread neglected zoonotic disease caused by pathogenic spirochetes of the Leptospira genus. Horses can act as subclinical reservoir hosts, which are characterized as asymptomatic carriers that persistently excrete leptospires through their urine and transmit the disease. Horses play an important role in the lives of Connecticut (CT) residents in the form of leisure pursuits and related business activities. Nevertheless, there is a limited understanding of horse exposure to Leptospira in CT. This investigation sought to determine the prevalence of anti-Leptospira antibodies in horses in Connecticut, US. A total of 397 sera were tested by the microscopic agglutination test (MAT). The antigen panel included 40 strains representing 26 serogroups and four autochthonous isolates (no determined serogroup). The overall horse seropositivity (established as a titer =1:100) was 61.5% (244/397). The most detected serogroups were Iquitos, Djasiman, Grippotyphosa, Australis, Pomona, and serovar Room22 strain GWTS1. Cross reaction for more than one serogroup was found in 81/244 (33.2%). As a limitation, the MAT does not differentiate between natural exposure and vaccination. However, Leptospira bacterin for horses includes only serogroup Pomona in the U.S. Therefore, after eliminating Pomona results to reduce potential vaccination bias, the seroprevalence was 204/397 (51.4%). Our results showed a high seroprevalence of leptospirosis in Connecticut and strong evidence that animals were potentially exposed to serogroups/serovars not included in commercial bacterins. Further studies to attempt isolation and genotyping of the pathogen from horses are necessary to better understand the role of horses in the epidemiology of leptospirosis. This information will support diagnostic strategies, vaccine recommendations, risk assessment, and public health actions that can reduce spillover transmission and the impact of this important zoonotic disease.