Serologic evidence of equine leptospirosis in the northeast United States.

Serologic testing for leptospiral antibody was conducted with the macroscopic agglutination test on 1,346 equine serum samples. These were collected from clinically normal horses in 123 purebred herds in the Northeast. Sixty-eight samples (5%) from the population tested reacted at significant levels (1:40 or higher) to one or more of the 5 serotype antigens used. These reactors were from 38 (31%) of the herds tested. Reactions to serotype pomona predominated in 25 (72%) of these 38 herds. Smaller numbers of herds had reactors to canicola, icterohemorrhagiae and grippotyphosa. No significant reactions to serotype hardjo were detected.