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Leptospirosis is a zoonotic bacterial disease caused by Leptospira interrogans. There is a serologic evidence that horses are exposed to L. interrogans and, as a shedder of these organisms, can be a threat to humans. We examined risk factors associated with the risk of testing seropositive to three L. interrogans serovars (L. icterohaemorrhagiae, L. grippotyphosa, and L. canicola) in the horses of New York State, in order to understand the epidemiology of the disease and suggest strategies to control and prevent equine leptospirosis. To carry out this study, blood samples were collected from a random sample of 2551 horses and tested for the presence of antibodies to the above serovars using the microscopic agglutination test. Samples with a titer $100 were considered positive. Clinical and demographic data were collected on each horse, the farms' management practices and ecology. Logistic regression analysis was used to develop a multivariate indexing system and to identify factors significantly associated with the risk of leptospirosis. Four indices were developed based on the possible sources of exposure: rodent exposure index; wildlife exposure index; soil and water index; and management index. The soil and water index was significantly associated with the risk of exposure to all three serovars. Management was positively associated with L. icterohaemorrhagiae and L. canicola. Density of horses turned out together was positively associated with the risk of exposure to L. grippotyphosa. We concluded that indirect exposure of horses to L. interrogans through contaminated soil and water appears to be significantly associated with the risk of exposure to all three serovars. Management appears to play an important role in the exposure to L. interrogans. Modification of management practices might reduce the horses' risk of exposure and hopefully minimize the human hazards.

Objective: To determine and quantify risk factors associated with exposure of horses to the following serovars of Leptospira interrogans: pomona, autumnalis, and bratislava., Animals: 2,551 horses were randomly selected from a target population during the period of May 1991 to August 1993., Procedures: Blood was collected from the horses and tested for antibodies to serovars, using the microscopic agglutination test. A titer > or = 1:100 indicated seropositivity. Information was collected on each horse, its environment, and each farm's management practices. Logistic regression analysis was used to develop a multidimensional indexing system for indices of exposure and to identify factors significantly-associated with the risk of seropositivity. These indices were: 1) rodent exposure; 2) wildlife exposure; 3) soil and water; and 4) management., Results: Rodent exposure index value was associated with the risk of exposure to all 3 serovars. Management index value was positively associated with the risk of exposure to serovars pomona and bratislava, but not with risk of exposure to serovar autumnalis. Soil and water index value had a positive association with risk of exposure to serovars pomona and autumnalis, but not to serovar bratislava. The wild-life index value and the population density of horses turned out together were associated with the risk of exposure to serovar autumnalis. Age of horse in years was associated nonlinearly (years) and linearly (years) with the risk of exposure to serovars autumnalis and bratislava, and only linearly with the risk of exposure to serovar pomona., Conclusion: Risk of seropositivity to the 3 serovars of L interrogans varies according to age, management practices, population density of horses turned out together, and the values of the rodent exposure, wildlife exposure, and soil and water indices.