A Randomised, Double-Blind Pilot Study of Enzyme-Potentiated Desensitisation for Prophylaxis of Large Local Reactions to Mosquito Bites

Primary Objective. To test the hypothesis that two injections of enzyme-potentiated mosquito antigen significantly reduce the size of experimental mosquito bites in participants with LLR-MB. Design. Randomised, double-blind, placebo-controlled, parallel group comparison over 3 months. Setting. Hospital outpatient clinic. Participants. Fifty adult participants of both sexes. Interventions. Two injections of mosquito antigen or matching placebo, 6 weeks apart. Main Outcome Measures. Early (1 hour) and late (24 hours) mean square root of erythema area (SREA) following controlled mosquito bite with the second bite given at least 6 weeks following the final injection. Results. At 1 hour, mean SREA was slightly higher in the EPD group compared to placebo after adjusting for baseline values (0.46, 95% CI -6.11 to 7.03), but this was not statistically significant (P = 0.89, ANCOVA analysis); neither were the results at 24 hours (-2.58, 95% CI -11.73 to 6.57) (P = 0.57). The proportion of participants experiencing a decrease in wheal size at 1 or 24 hours was similar between groups. Conclusions. EPD was not demonstrated to be effective for immediate or delayed LLR-MB. Methodological problems included a high variability in LLR-MB between subjects, suggesting that a crossover design should be used in future.