Equine ocular onchocerciasis: histopathologic study.

The research article investigates equine eye abnormalities related to ocular microfilariae infections, featuring a close study of a treated horse to assess treatment effects, and finding no distinct abnormalities associated with such infections.

Study Overview

• The aim of the research was to investigate the presence of ocular microfilariae in horses and their association with eye abnormalities.
• A total of 368 equine eyes were examined both clinically and histologically. Histological examinations allow for the close study of the microscopic structure of the tissues.
• The horses were naturally infected with Onchocerca sp, a type of parasite.
• In addition to the general study, one horse with ocular microfilariae was treated and sampled over time to observe the microfilariae’s response to treatment.

Findings

• Out of the examined eyes, 40 of them had microfilariae present in the conjunctiva, which is the mucous membrane that covers the front of the eye and lines the inside of the eyelids.
• Notably, there were no distinguishable clinical abnormalities associated with the presence of these microfilariae.
• The horse that was treated for ocular microfilariae was given diethylcarbamazine, a common treatment for parasitic infections, daily for two weeks.
• Tissue samples were collected from this horse before, during, and after the treatment period, and were compared histologically.
• There were notable changes in the distribution of microfilariae and inflammatory cells. Particularly, microfilariae seemed to have moved from the conjunctival stroma, the connective tissue of the conjunctiva, into the perilimbal corneal stroma, the connective tissue around the edge of the cornea. Inflammatory cells were also found to be more abundant in the perilimbal tissues.
• However, the tissue samples obtained before and after the treatment did not markedly differ in their appearance.

Implications

• The study suggests that ocular microfilariae infections in horses may not lead to distinct and easily observable eye abnormalities, making it difficult to identify the condition solely based on clinical symptoms.
• The histological differences observed during the treatment of the specific case provide valuable insights into how the microfilariae and the horse’s body react to treatment.
• More extensive research may be necessary to determine the impact of such movements in the long term, and the potential effects on equine ocular health.