RESUMO
OBJECTIVE: The purpose of this study was to determine whether 400 µg/kg oral ivermectin is able to kill Ixodes scapularis nymphs and adult female ticks feeding on humans. METHODS: Ten study subjects each wore 2 ostomy bags, the one containing 24 I scapularis nymphs, and the other containing 24 I scapularis adult females. Twenty-four hours after the ostomy bags were attached, study subjects received either 400 µg/kg ivermectin or placebo. Thirty hours after the ivermectin or placebo was consumed, the ticks were removed, and mortality determined in a double-blinded manner. RESULTS: Eleven percent of the I scapularis nymphs attached in the ivermectin group compared with 17% in the placebo. Mortality for the I scapularis nymphs that attached at the time of removal was 55% in the ivermectin group and 47% in the placebo group. Mortality for the I scapularis nymphs 5 days after removal was 92% in the ivermectin group and 88% for the placebo. Three percent of the I scapularis adults attached in the ivermectin group compared with 9% in the placebo group. Mortality for I scapularis adults was 0% on day 3 and 33% on day 8 for both the ivermectin and placebo groups. There were statistically insignificant differences in the mortality rates between I scapularis nymphs and adults exposed to ivermectin or placebo. CONCLUSIONS: There were a high number of ticks that died in both groups but the data do not support our hypothesis that ivermectin can kill I scapularis. The study was not designed to determine whether it could prevent the transmission of tick-borne illness.