Experimental Leptospira interrogans serovar Kennewicki infection of horses.

Background: Little information is available about experimental induction of leptospirosis in horses.

Objectives: Determine serologic, hematologic responses of horses to Leptospira interrogans serovar Kennewicki infection.

Animals: Four adult horses seronegative for leptospirosis.

Methods: Experimental and observational study. Horses were challenged with an equine isolate of L. interrogans serovar Kennewicki at 2 different doses and different inoculation sites. After challenge, the horses were monitored for 60 days. Blood, urine, and aqueous humor samples were collected at intervals until euthanasia 60 days after infection.

Results: Pyrexia (39.3-40 degrees C) occurred as early as 1 day after challenge with 10x10(8)Leptospira divided equally between topical ocular and intraperitoneal injection in 2 horses. Leptospires were recovered from the blood and urine but not from the aqueous humor of the 2 febrile horses. The sera of all 4 challenged horses developed microscopic agglutination test antibody after challenge and remained relatively constant for 21 days. Titer to cross-reacting strains declined earlier than titer to the challenge strain.

Conclusions: Clinical disease in experimentally infected horses can be mild or inapparent in Leptospira infected horses. Repeated serologic testing can allow recognition of the infecting serovar. In febrile horses, Leptospira can be isolated from blood while isolation from the urine can occur after fever has subsided.