The prevalence of equine leptospirosis in New York State

We carried out a cross-sectional study to determine the seroprevalence of seven different serovars of Leptospira interrogans in horses in New York State and examine the geographic distribution of the disease in the state. A random sample of 2,967 horses was selected from the equine population in New York State using the 1988 New York State Equine Census as a sampling frame. The samples were tested for the presence of antibodies against seven serovars: L. pomona, L. hardjo, L. icterohaemorrhagiae, L. grippotyphosa, L. canicola, L. autumnalis, and L. bratislava. The microscopic agglutination test was used to determine seropositivity at a range of dilutions from 1:100 to 1:12800. A tiler of ≥ 100 was considered positive. We also examined the association between seroconversion at higher (≥ 1600) liters among those serovars. Cluster analysis was used to examine the distribution of the disease for special pattern or clustering. The following prevalences were determined: L. pomona (7.6%), L. hardjo (1.0%), L. icterohaemorrhagiae (11.3%), L. grippotyphosa (6.5%), L. canicola (16.2%), L. autumnalis (35.1%), and L. bratislava (40.7%). The majority of the titers for all serovars were relatively low. Most of the samples tested positive for L. pomona had titers ranging from 100 to 400. For all the other serovars, most samples tested positive had titers ranging from 100 to 200. We found significant associations of seroconversion between all pairs of serovars except L. grippotyphosa and L. pomona, and L. grippotyphosa and L. autumnalis.