UKVDL Records Rise in Equine Leptospirosis Cases

As Kentucky progresses through a near-record rainfall year, the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) has begun observing equine leptospirosis abortions. Following is a summary of what the UKVDL is seeing in eastern Kentucky.

Microscopic agglutination test (MAT) titer results on sera (blood serum) submitted to UKVDL through the end of November 2011 shows some high titers consistent with wet years in the past (see table at left).

Five abortions have been confirmed to date either by PCR or fluorescent antibody (FA) testing.

An interactive map displaying the geographic locations of clinics submitting sera for MAT titers 1:200 or greater is available online.

Leptospirosis Overview: Leptospirosis is a transmissible disease of animals and humans caused by infection by the spirochete Leptospira. All the pathogenic leptospires were formerly classified as members of the species Leptospira interrogans; however, the genus has recently been reorganized and pathogenic leptospires are now identified in 17 named species and four genomospecies of Leptospira. More than 200 distinct leptospiral serovars (strains) have been recognized, and these are arranged in 23 serogroups. Previous studies in Kentucky suggest that leptospirosis was the leading cause of abortion in domestic animals--mostly horses--in 1989, and the third most common bacterial cause of abortion diagnosed from 1986 through 1991. In the high-rainfall reproductive season of 2006 more than $3 million in foals were lost in the Bluegrass alone.

Clinical leptospirosis in horses, cattle, and companion animals is often associated with recent exposure, directly, or indirectly, to surface water contaminated by rat urine. Horses typically live in an environment that combines a pasture and stable shared with a number of small mammals. In winter most horses are fed roughage, which is almost inevitably contaminated by mouse, and often rat, urine. Cattle, dogs, and horses are thus indirectly exposed to animals that can be leptospire reservoirs.

Definitive diagnosis of leptospirosis has traditionally been very difficult because culture of leptospira takes up to 13 weeks and is often hampered by other bacterial contamination. The gold standard for diagnosing leptospirosis has been the MAT, in which patient sera are reacted with live antigen suspensions of major leptospiral serovars. However, MAT works only with serum, cannot be used with urine or fresh tissues, and it is often difficult to differentiate an active infection from previous exposures. Other diagnostic methods include serological assays such as ELISA, fluorescence antibody, and immunohistochemistry.

However, a new real-time PCR test can detect leptospiral DNA, allowing equine practitioners to diagnose infected animals as well as carrier animals that might be shedding into the environment. Real-time PCR is extremely sensitive, specific, and works with tissue samples regardless of being fresh or putrefied. In addition, urine samples in which infected or carrier animals shed can be tested.

For testing using the real-time PCR test, UKVDL requires a minimum of 10 mL urine and/or 20 grams fresh kidney to be sent in leak-proof containers with enough chill packs to keep specimens cool. The cost is $20 per animal. Testing specimens in question can confirm whether leptospirosis organisms are present. If organisms are confirmed, an appropriate treatment can be selected and animals shedding leptospires in their urine can be detected. The real-time PCR test shortens the time required to confirm a clinical diagnosis, leading to early prevention of the spread of leptospira organisms and the minimization of human exposure to these organisms.

Other tests for leptospirosis from UKVDL include MAT titers and fluorescent antibody testing.

Source: December 7 University of Kentucky Veterinary Diagnostic Laboratory edited bulletin

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