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Equine leptospirosis is typically a sporadic disease. The primary leptospiral-associated equine clinical disease presentations include; recurrent uveitis, late-term abortion and acute renal failure. Infection is acquired through exposure to the organism via the mucous membranes or abraided skin. The leptospiral organisms are shed in the urine of infected horses (additionally the placenta, fetal fluids and urine of the mare in abortion cases) and a number of wildlife hosts which can shed Leptospira spp. in the urine. 

Seroprevalence data from healthy horses indicate that it is common for horses to carry titers to multiple serovars. Multiple serovar titers can result from direct exposure to these serovars, cross-reactivity of the MAT (microscopic agglutination test) between different serovars or both. In diseased horses, Leptospira interrogans serovar pomona is the most commonly incriminated pathogen/serovar in the U.S.

Vaccine: 

There is currently one vaccine approved for use in horses. It is a killed, whole cell bacterin. 

The product is labeled for vaccination of healthy horses 6 months of age or older as an aid in the prevention of leptospirosis caused by Leptospira interrogans serovar pomona.
The vaccine has demonstrated safety in foals as young as 3 months of age. Efficacy of this product was demonstrated utilizing an intraperitoneal Leptospiral challenge model. Vaccinated horses did not develop leptospiremia or leptospiuria as compared to controls.

The duration of immunity of this product has not been determined. 

Vaccination Schedule:  

Horses 6 months of age or older: Initial two dose series, 3 to 4 weeks apart. Annual revaccination. 

Pregnant mares: The product has demonstrated safety in pregnant mares during the 2nd trimester. Additional safety studies in pregnant mares are ongoing.