Leptospiral Uveitis Helps Vaccine Research

Ashutosh Verma, BVSc, MVSc, graduate research assistant in the laboratory of John Timoney, BSc, MVB, MRCVS, MS, PhD, DSc, Keeneland Association Chair in Equine Science, at the University of Kentucky's Gluck Equine Research Center in Lexington, recently presented his leptospiral equine recurrent uveitis (ERU, or moon blindness) research. Verma has identified leptospiral proteins that actually prime immune responses in the horse's eye for ERU.

Leptospirosis is a widespread zoonosis (the bacteria affects both humans and animals) throughout the world and can cause abortion, infertility, lowered milk production, and ERU. The disease can be contracted through cuts, abrasions, even intact mucus membranes or ingesting contaminated soil or feedstuffs.

There are six major serogroups of Leptospira, which can be further divided into over 500 serovars. Seven serovars affect the horse: L. autumnalis, L. bratislava, L. canicola, L. grippotyphosa, L. hardjo, L. icterohemmoragica, and L. pomona.

"L. pomona is the most common infectious cause of ERU in North America," said Verma. "There is no vaccine for horses, but extra-label (off-label) use of cattle vaccines (in horses) could cause future problems."

After studying ocular fluids from uveitic horses, Verma found that certain leptospiral proteins stimulate antibodies that can react with equine ocular tissue and enhance the disease process. "Several leptospiral proteins are involved with the antibody response of ERU," said Verma. "Some leptospiral proteins which share epitopes (the site on the surface of an antigen molecule to which a single antibody molecule binds) with eye components may need to be excluded from a future vaccine because a vaccine containing these leptospiral proteins would actually prime horses for ocular complications if there is subsequent exposure.

"One of the newly identified proteins may in itself be a vaccine candidate, but that is not proven at this point,” he added.

Until a vaccine against leptospirosis is created and approved for use in horses, the best fight against the disease is the education of horse owners and clinicians, says Verma. "Leptospirosis in general is a widely underdiagnosed disease. Educating owners about the epidemiology--rodents and other wildlife are important carriers of the bacteria on farms--and about uveitis in general will be a good starting point. Also, clinicians should be aware of the importance of the disease in the region." The most common clinical signs of leptospirosis are mild fever with anorexia, but horses with severe cases can present with anemia, jaundice, depression, and weakness. Recurrent uveitis develops anytime from two to eight months following the initial leptospiral infection.

As Verma and others work on future leptospirosis research and a vaccine against the disease, Verma notes, "Veterinarians can send blood samples from uveitic horses for leptospira testing to our lab, which we do without charge." Call 859/257-4757 if you have a blood sample you would like tested.

About the Author

Marcella M. Reca Zipp, MS

Marcella Reca Zipp, M.S., is a former staff writer for The Horse. She is completing her doctorate in Environmental Education and researching adolescent relationships with horses and nature. She lives with her family, senior horse, and flock of chickens on an island in the Chain O'Lakes.

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