Equine Leptospirorosis Vaccine Now Available

Equine Leptospirorosis Vaccine Now Available

Leptospirosis.  Veterinarians face it; horse owners dread it.

Though well-handled in many species, this bacteria has remained mysterious and problematic in the equine world.  Cattle, dogs and cats have benefited from  leptospirosis vaccines for years.  At last, there may be one for horses.

The Food and Drug Administration recently approved an intramuscular vaccine developed by a group of veterinarians and researchers in conjunction with pharmaceutical company Zoetis, the world's largest producer of medicine and vaccinations for pets and livestock. There is optimism that the medication will reduce the equine infection, which can effect a variety of organs.

Thehorse.com defines Leptospirosis as a zoonotic (transmitted between animals and man) bacterial disease found worldwide that can affect any mammalian species, including humans, wildlife, rodents, livestock, and, yes, horses. The disease is caused by leptospires, which are motile (capable of moving) bacteria called spirochetes. Leptospires are subdivided into serovars and serogroups (subgroups). Those of importance to the horse include pomona, grippotyphosa, hardjo, bratislava, canicola, and icterohaemorrhagiae. The incubation period for leptospirosis in horses is one to three weeks.

Craig Carter, DVM, PhD, director of the University of Kentucky's Livestock Disease Diagnostic Center and professor of epidemiology, tells us horses become infected through mucous membranes of the eyes or mouth and sometimes through broken skin by contact with infected urine, blood, or tissues. Horses can become infected by eating hay or grain that has been contaminated by infected urine, or they can contract it by drinking from standing water that has been similarly affected. Cattle could introduce infected urine into ponds or other standing water.

Leptospirosis presents differently in different animals.  In dogs, it presents as flu-like symptoms; in cattle  as reduced milk production and abortion. In horses however, the bacteria appear to collect in different parts of the body, with the most common being the eyes, kidneys, or reproductive organs, sometimes leading to very different symptoms between patients. Recurring “moon blindness” or uveitis, is one of the most common indicators of a leptospirosis infection. Uveitis leads to eye swelling, cloudiness, discharge, and sensitivity towards light.  Less commonly, kidney inflammation and failure can be blamed on the bacteria.

Abortion is also a common symptom of leptospirosis, with most occurring late in pregnancy and rare instances of foals being born alive with an active infection. In a study that included 3527 cases of abortion, still birth and perinatal death, fetoplacental infection caused by bacteria represented 628 cases,  of which  leptospirosis was identified in 78 (12.5%)

Some veterinarians had been using the cattle leptospirosis vaccine in horses as a makeshift in the hope of equine developments; others believed that the bovine formula could prove detrimental to equines.  “My contention has always been that I could never take the risk of vaccinating the horses under my care with the cattle vaccine, because the value of the mares would be such that if I predisposed one of them to laminitis (inflammation of the sensitive structures in the hoof called the lamellae), it wouldn’t be justified based on the risk,” stated Dr. Stuart Brown of Hagyard Equine Medical Institute.

The new vaccine is now available to practitioners for use in equine herds.

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