Equine recurrent uveitis or periodic ophthalmia is a long lasting, painful eye disease that results in inflammation in some of the deeper eye structures, resulting eventually in blindness. As the name implies, recurrent uveitis typically occurs multiple times, which increases the chances for damage to the eye and eventual vision impairment. It affects a wide range of horse breeds and is difficult to treat effectively.
Causes of Moon Blindness
The cause of this disease has been attributed to a variety of infectious agents and/or immune system hyper-reactivity. Since the early 1950’s, published reports have implicated leptospirosis in recurrent uveitis. Leptospira is a bacterial organism that is found commonly throughout Australia and is widespread in cattle herds. The organism can persist for many years in soil where cattle have been housed, for example on old dairy sites.
A team of researchers at the University of California, Davis has completed a study to determine if leptospiral infection is associated with equine recurrent uveitis. More than 300 cases of recurrent uveitis were diagnosed at the UC Davis Veterinary Medical Teaching Hospital (VMTH) from 1990-1996. In previous studies the association of leptospirosis with uveitis has revolved around serological assays (blood tests). New methods of DNA analysis have facilitated a unique opportunity to study this disease further.
Research of Moon Blindness
The study utilized advanced genetic and diagnostic approaches, researchers examined eye fluid samples from horses with uveitis that were presented to the VMTH. The samples were assayed by PCR for the presence of DNA sequences specific for the leptospirosis organism.
This is the first study that used fluid samples from the eye to detect the presence of leptospirosis using the PCR technique. Blood samples from these horses were also assayed for elevated immunoglobulins levels indicative of leptospiral infection. Eye fluid samples were also cultured in a leptospiral growth medium.
The researchers were able to identify leptospirosis as a major cause, if not the primary cause, of equine recurrent uveitis. It was determined that out of 36 horses tested, 35 of the eye fluid samples tested positive for leptospiral DNA and that of the 13 blood samples that were tested, 10 were positive for leptospiral antibodies. It was also found that four of the eye fluid samples cultured were positive for leptospires.
This study determined that leptospirosis is a cause of recurrent uveitis in horses. With this knowledge, researchers can develop effective treatment and vaccines for this disease.