Equine ocular pathology ascribed to Onchocerca cervicalis infection: a re-examination.

The research paper explores the relationship between Onchocerca cervicalis, a parasitic worm, infection and ocular issues in older horses from various regions in the United States. The study finds that no definite link can be established between the presence of O. cervicalis and specific eye pathology changes.

Research Methodology

• The researchers studied eyes from a total of 292 horses ranging from 15 to 20 years old. These horses originated from different regions across the United States, specifically from the Eastern, Southeastern, and Midwestern areas.
• The examination was dual-focused, investigating the presence of Onchocerca cervicalis microfilariae (smaller larval stages of the parasite) and analyzing any apparent changes in both the anterior and posterior segments of the ocular region.

Findings and Analysis

• Out of these 292 horses, 153 (52.4%) tested positive for dermal microfilariae. The distribution, however, ranged from as low as 0.03 to as high as 5,364 per milligram.
• Among the horses that tested positive for the parasite, 60 displayed changes in the anterior segment of their eyes. Straightforwardly translated, these changes were not exclusive to the horses infected with Onchocerca cervicalis.
• An additional 58 horses with visible eye pathology changes showed no traces of any dermal microfilariae, further placing the exclusivity of the connection in question.
• Parasitic microfilariae were discovered in the ocular tissues of 18% of the studied horses; however, the range of microfilariae distribution was quite wide (from 0.07 to 29 per milligram).
• All horses that showed signs of ocular microfilariae were also positive for dermal microfilariae. Although this stat indicates potential multifaceted infections, it does not necessarily suggest that dermal infection will contribute to ocular problems.
• The most common pathological changes found in these horses included punctate scleral opacities (14.0% of horses, with 7.2% of them having microfilariae), temporal scleral viteligo (11.6%, with 6.8% having microfilariae), and uveitis (11.0%, 6.2% with microfilariae).
• Only a few significant changes in the posterior segment of the eye were seen, indicating that the greater part of the changes might occur in the anterior segment.

Conclusion

• The data collected from this research does not conclusively endorse the hypothesis that ocular pathological changes can act as reliable indicators for the presence of an Onchocerca cervicalis infection.
• The link between the parasite and eye health in horses remains speculative and demands further research, as pathological changes appear to be present in both infected and non-infected horses.