Successful treatment of ocular equine microfilariasis (Setaria species) with ivermectin.

This research conducted a successful experiment using the off-label use of Ivermectin in treating ocular setariasis (a parasitic infection of the eye caused by Setaria species) in four horses presented to the Veterinary Medical Teaching Hospital, University of Agriculture, Faisalabad, Pakistan. Typically, this condition is treated surgically, but this study provides significant evidence that Ivermectin could also be an effective and more practical form of treatment.

Methodology and Findings

• In the study, four horses (equids) of different breeds, sexes, and ages were chosen. Each had body condition scores between 2 and 4, and were noticed to have a whitish parasite moving swiftly in the aqueous humour of their left eye.
• Except for case 3, which was presented for lameness treatment, other clinical signs like photophobia, corneal opacity, blepharospasm, mild lacrimation, and head tilt were noticed in the other horses.
• The horses were diagnosed with ocular setariasis through microscopic examinations of their blood samples, where motile microfilariae were found. This was confirmed through Knott’s test, a technique for the detection of microfilariae.
• All the horses were treated with a single subcutaneous injection of 300 µg/kg ivermectin and oral administration of 4 to 5 g of aspirin daily for four days. Seven days after the ivermectin treatment, no microfilaria was detected in the blood samples of cases 1 and 4.
• Re-examination 10 days after ivermectin treatment showed that the ocular parasite was still present, but its movement had markedly slowed. As days 15 and 17 came around, the parasite in cases 1, 2, and 4 died.

Implications and Conclusions

• Ocular setariasis is traditionally treated through surgery which, apart from its complexity, has advent risks and inconsistencies. However, this study demonstrated that ivermectin could also provide an effective treatment.
• Although the off-label use of ivermectin for this condition took about 15 days for the parasite inside the eye to die, this result remains significant considering the impracticality and complexity of repetitive surgical treatments.
• The study suggests that, in conditions where surgical operations are challenging, ivermectin might be a suitable alternative for effectively treating ocular setariasis.
• Moreover, the research attempts to infer that microfilaraemia could be one of the factors responsible for the poor body condition of these horses, given that two of the treated cases with microfilaraemia possessed leucocytosis and an accelerated ESR.