This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents.

The last report of equine leptospiral-induced abortions was in the April 2004 issue of Equine Disease Quarterly. Since this report, additional cases of leptospiral-induced abortions have been diagnosed at the Livestock Disease Diagnostic Center at the University of Kentucky. For reporting purposes, a foaling year begins July 1 and ends June 30 of the subsequent year. Therefore, the following report includes cases diagnosed for the foaling years 2005, 2006, and most of 2007.

Prevention and Control of Leptospirosis Since no approved vaccine against leptospirosis in horses is available, prevention of leptospiral-induced abortion is best achieved by minimizing exposure to the bacteria. Prevention is aimed at avoiding direct contact with the urine of wildlife and cattle. Indirect contact with urine that might be present in environmental water sources, feed, and bedding should also be avoided. Practical measures that can be taken to reduce exposure to potentially urine-contaminated areas include strict control of wildlife around barns and feeding hay and grain off the ground. Other domestic species on the premises should be vaccinated against leptospirosis if an approved vaccine exists for that species. Following a leptospiral abortion, the area where the mare aborted should be thoroughly cleaned. The aborting mare should be isolated, since shedding of leptospira can continue for weeks. Antibiotic therapy can shorten the period of shedding. Serologic testing of pregnant mares can identify mares possibly at risk of aborting due to leptospirosis. High-titer mares should be isolated, and negative, or low-titer, mares should be retested in two to three weeks. A course of antibiotics in mares with high titers may prevent or lessen fetal infection and prevent abortion, although this treatment has not been evaluated in controlled studies.

Sixty-five leptospiral-induced abortions have been diagnosed during the last three foaling years (July 1, 2005, through April 30, 2007). Breeds of horse and number of cases involved were Thoroughbred, 59; Standardbred, 5; and mixed breed, 1. Over the three-year period, the number of leptospiral-induced abortions on farms varied, with 38 farms having a single leptospiral-induced abortion, two farms having two abortions each, three farms with three abortions each, one farm with four abortions, and a single farm with 10 abortions over the three-year period.

Leptospirosis is a zoonotic bacterial disease with global distribution. Virtually all species of mammals are susceptible. The bacteria, called “spirochetes,” are 6-20 microns in length, 0.1-0.2 microns in width, motile, and helically coiled. The genus is divided into multiple species and is further divided into more than 250 serovars. The term “serovar” commonly is used to describe a specific strain of Leptospira spp. The serovars with antigens in common are placed in serogroups for diagnostic convenience. The predominant serovar affecting horses varies with country and region. In Central Kentucky, serovars commonly affecting horses and causing infections include L. interrogans serogroup Pomona serovar kennewicki and L. kirschneri serogroup Grippotyphosa serovar grippotyphosa. Organisms from serogroup Hardjo rarely have been detected in horses in Central Kentucky.

Serologic results indicated that serovar kennewicki of the Pomona serogroup was responsible for 50 (77%) of the abortions and grippotyphosa for nine (14%) of the leptospiral-induced abortions for the past three foaling seasons. The serovar was undetermined for six (9%) abortions. Eight (12%) of the leptospiral-induced aborted fetuses were serologically negative. Microscopic agglutination testing and the diagnosis were made via the identification of spirochetes by direct fluorescent antibody test, microscopic identification with the Warthin-Starry staining method, and/or maternal serology.

The Livestock Disease Diagnostic Center has diagnosed 315 cases of leptospiral-induced abortion in Central Kentucky over the past 19 foaling seasons. Almost all cases were due to either kennewicki (260 cases, 83%) or gripptotyphosa (33 cases, 10%). Figures 1 and 2 detail, by foaling year and month, the number of confirmed cases of leptospiral-induced abortions or neonatal deaths for this period