Insecticide resistance is a growing threat to malaria vector control. Ivermectin, either administered to humans or animals, may represent an alternate strategy to reduce resistant mosquito populations. The aim of this study was to assess the residual or delayed effect of administering a single oral dose of ivermectin to humans on the survival, fecundity and fertility of Anopheles arabiensis in Ethiopia.
Six male volunteers aged 25-40 years (weight range 64-72 kg) were recruited; four of them received a recommended single oral dose of 12 mg ivermectin and the other two individuals were untreated controls. A fully susceptible insectary colony of An. arabiensis was fed on treated and control participants at 1, 4, 7, 10 and 13 days post ivermectin-administration. Daily mosquito mortality was recorded for 5 days. An. arabiensis fecundity and fertility were measured from day 7 post treatment, by dissection to examine the number of eggs per mosquito, and by observing larval hatching rates, respectively.
Ivermectin treatment induced significantly higher An. arabiensis mortality on days 1 and 4, compared to untreated controls (p = 0.02 and p < 0.001, respectively). However, this effect had declined by day 7, with no significant difference in mortality between treated and control groups (p = 0.06). The mean survival time of mosquitoes fed on day 1 was 2.1 days, while those fed on day 4 survived 4.0 days. Mosquitoes fed on the treatment group at day 7 and 10 produced significantly lower numbers of eggs compared to the untreated controls (p < 0.001 and p = 0.04, respectively). An. arabiensis fed on day 7 on treated men also had lower larval hatching rates than mosquitoes fed on days 10 and 13 (p = 0.003 and p = 0.001, respectively).
A single oral dose of ivermectin given to humans can induce mortality and reduce survivorship of An. arabiensis for 7 days after treatment. Ivermectin also had a delayed effect on fecundity of An. arabiensis that took bloodmeals from treated individuals on day 7 and 10. Additional studies are warranted using wild, insecticide-resistant mosquito populations, to confirm findings and a phase III evaluation among community members in Ethiopia is needed to determine the impact of ivermectin on malaria transmission.