Repellent effect of topical deltamethrin on blood feeding by Culicoides on horses.
Authors: Robin M, Archer D, McGowan C, Garros C, Gardès L, Baylis M
Journal: The Veterinary record
Summary
# Repellent effect of topical deltamethrin on blood feeding by Culicoides on horses African horse sickness, transmitted by Culicoides biting midges, poses a significant biosecurity concern for UK equine populations, and the Department for Environment, Food and Rural Affairs currently recommends topical deltamethrin as a control measure despite the absence of equine efficacy data. Robin and colleagues investigated whether 1% deltamethrin solution applied topically to horses reduced blood feeding by Culicoides species, using a controlled study design where three horse pairs were housed in partially enclosed cages; one horse per pair received deltamethrin treatment, with Culicoides sampling conducted in four pre-treatment and four post-treatment sessions. The most prevalent species collected—*Culicoides chiopterus*, *C. dewulfi*, *C. obsoletus*, *C. scoticus* (44.3%), and either *C. pulicaris* or *C. punctatus* (34.7%)—demonstrated the highest blood feeding rates, confirming their epidemiological importance as potential AHS vectors; however, deltamethrin treatment produced no significant reduction in blood feeding rates compared with untreated controls. These findings suggest that topical deltamethrin applied to individual horses offers limited practical benefit for preventing Culicoides feeding and should prompt practitioners to reconsider its recommendation as a primary control strategy, although the study design could not assess whether population-level effects or outbreak-scenario applications might alter this conclusion.
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Practical Takeaways
- •Topical deltamethrin alone is not an effective strategy to prevent Culicoides from feeding on individual horses and should not be relied upon for AHS prevention at the horse level
- •While this study shows no benefit at the individual horse level, wider population-level effects of deltamethrin on vector numbers remain unknown and warrant further investigation
- •Additional or alternative vector control methods beyond topical deltamethrin should be considered for AHS risk management in susceptible horse populations
Key Findings
- •Topical deltamethrin (1% solution, 10ml) had no significant effect on blood feeding by Culicoides on treated horses
- •C. chiopterus, C. dewulfi, C. obsoletus and C. scoticus represented 44.3% of collected midges and showed higher blood feeding rates than other species
- •C. pulicaris and C. punctatus represented 34.7% of collections and were also more likely to have blood fed
- •These highly abundant species are more likely to serve as AHS vectors if the virus reaches the UK