The effect of a topical insecticide containing permethrin on the number of Culicoides midges caught near horses with and without insect bite hypersensitivity in the Netherlands.

This study investigated the use of a topical insecticide containing permethrin on horses and its effectiveness in reducing the number of Culicoides midges, insects known to cause hypersensitivity reactions.

Background of the Study

• The problem being investigated here is insect bite hypersensitivity (IBH) in horses, a condition predominantly caused by the Culicoides species of midges, although other insects can also contribute.
• A lack of reliable treatments for this condition has led to the trial of numerous preventive and therapeutic measures, among these is the application of topical insecticides on horses; this study particularly evaluated an insecticide containing 3.6% permethrin.

Methodology of the Randomised Control Trial

• The researchers worked with seven pairs of horses that were placed within a tent trap meant for capturing Culicoides and other insects attracted to horses.
• Over two consecutive nights, the horses were exposed to these traps. On the first night, both horses were untreated (control group), and post this session, one horse from each pair was treated with the insecticide (treatment group), while the untreated horses (control) were kept separately.
• On the second night, the treatment and control horses were placed back inside the tent trap and insects were again collected to evaluate the effect of the insecticide on reducing insect attraction.

Findings of the Study

• The study found that proportions of Culicoides trapped were in line with earlier studies (C. obsoletus 95.34% and C. pulicaris 4.54%). Interestingly, healthy horses attracted more Culicoides than those affected by IBH.
• The study noted a reduction in the number of Culicoides, the percentage of blood-fed C. obsoletus, and the total number of insects that were attracted to horses following segmentation of treated and untreated groups. However, this reduction was not statistically significant.
• No negative side effects were observed in horses that were administered with permethrin.

Conclusion of the Study

• While the study showed promise in the use of permethrin as a preventative measure for IBH, due to reducing midge attraction to horses, the results weren’t statistically significant, indicating a need for further research to validate these findings.
• The lack of observed side-effects in horses treated with permethrin is encouraging, suggesting that even if not entirely efficient in preventing Culicoides attraction, the insecticide may be safely used without fear of adverse effects.