Investigations on the Borrelia-etiology in equine recurrent uveitis (ERU)

Abstract

In the literature, Borrelia spp. have repeatedly been mentioned as a causative agent for uveitis in horses. As there are only few descriptions of diagnosed or assumed cases of Borrelia associated uveitis, and as in these cases an uncommon clinical course of the uveitis and severe systemical illness have been described, some doubts arose from these observations as to how important Borrelia infections are for the development of the recurrent uveitis in horses. Additionally, some studies could not detect any correlation between uveitis and Borrelia infection. This paper aimed at the evaluation of a possible association between Borrelia infections of equine eyes by examination of intraocular fluids from equine eyes suffering from typical clinical signs of recurrent uveitis. Samples from 105 eyes (from 88 horses) showing typical ERU by history and ophthalmologic examination were tested by real time PCR for Borrelia flagellin gene. These samples were also tested by real time PCR for LipL32 of pathogen Leptospira spp.. From each eye at least one sample was examined, in some cases two samples (aqueous and vitreous) have been taken within a few days. Altogether, 118 samples from eyes suffering from ERU were taken and tested by PCR for Borrelia and pathogen Leptospira spp. Additionally, 103 samples from 98 eyes not showing typical ERU were examined the same way. Those eyes were either sound or showed other signs than ERU, or suffered from glaucoma. In none of the samples from ERU eyes as well as in none of the samples from sound eyes or eyes with other diseases, Borrelia DNA could be detected. However, in 83 of the 118 samples (70%) from eyes showing ERU, or 80 of the 105 tested eyes (76%) respectively, leptospiral DNA could be found. In the control group only 3 samples out of 103, or 3 eyes out of 98 respectively, leptospiral DNA was ascertained. As a result, there was no hint on Borrelia infection in any of the eyes, but there was strong evidence for leptospiral infection in 76% of the eyes suffering from ERU by using solely PCR. In eyes with other diseases than typical ERU only 3% showed leptospiral DNA in their intraocular fluids. These 3 eyes belonged to the group suffering from glaucoma. Due to the literature it can be concluded that severely diseased horses with septicaemia and vasculitis might develop severe uveitis. But this uveitis is not the common one with recurrent attacks and quiet intervals, but some kind of not responding to any therapy and leading to blindness very soon in some cases. If horses survive septicaemia, uveitis will probably stop and show no further bouts. This is at least what is known from foals with uveitis during Rhodococcus septicaemia. If vision can be preserved over the general disease, no further damage of the eyes is expected. In very severe uveitis cases which do not respond to any treatment, other infectious agents than leptospires have to be considered, e.g. Micronema deletrix or Borrelia spp. In eyes showing the typical clinical course of ERU, there was no hint on a factual or at least a possible Borrelia etiology. In eyes suffering from other eye complaints than typical ERU, there was no hint on Borrelia infection either. On the other hand, leptospiral DNA could be detected in 76% of the eyes suffering from ERU, underlining the importance of Leptospira infections for recurrent uveitis in horses.