RISK-FACTORS ASSOCIATED WITH THE LIKELIHOOD OF LEPTOSPIRAL SEROPOSITIVITY IN HORSES IN THE STATE OF NEW-YORK

Objective-To determine and quantify risk factors associated with expos ure of horses to the following serovars of Leptospira interrogans: pom ona, autumnalis, and bratislava. Animals-2,551 horses were randomly se lected from a target population during the period of May 1991 to Augus t 1993. Procedures-Blood was collected from the horses and tested for antibodies to serovars, using the microscopic agglutination test. A ti ter greater than or equal to 1:100 indicated seropositivity. Informati on was collected on each horse, its environment, and each farm's manag ement practices. Logistic regression analysis was used to develop a mu ltidimensional indexing system for indices of exposure and to identify factors significantly associated with the risk of seropositivity. The se indices were: 1) rodent exposure; 2) wildlife exposure; 3) soil and water; and 4) management. Results-Rodent exposure index value was ass ociated 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 autumn alis. Soil and water index value had a positive association with risk of exposure to serovars pomona and autumnalis, but not to serovar brat islava. The wildlife index value and the population density of horses turned out together were associated with the risk of exposure to serov ar autumnalis. Age of horse in years was associated nonlinearly (years (2)) and linearly (years) with the risk of exposure to serovars autumn alis and bratislava, and only linearly with the risk of exposure to se rovar 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 e xposure, wildlife exposure, and soil and water indices.