Ivermectin Inhibits Zika Virus Replication in Vitro But Does Not Prevent Zika Virus Infection in Rhesus Macaques (Macaca mulatta).

Zika virus (ZIKV) outbreaks occur sporadically in tropical and subtropical regions. At present, there are no licensed vaccines or specific treatments available for ZIKV. Ivermectin is approved for use in humans as an antiparasitic drug. In this study, we conducted in vitro cell culture and in vivo experiments in rhesus macaque hosts and Aedes aegypti vectors to investigate the potential of ivermectin as an inhibitor of ZIKV infection. In LLC-MK2 mammalian cells, ivermectin inhibited ZIKV growth in vitro with 50% inhibitory concentration (IC50) values in the ranges of 7.4-21.3 µM and 4.0-11.6 µM for African and Asian genotypes, respectively. In C6/36 mosquito cells, ivermectin inhibited ZIKV growth in vitro with IC50 values in the ranges of 10.1-17.4 µM and 8.0-15.6 µM for the African and Asian genotypes, respectively. Despite these in vitro results, high-dose ivermectin prophylaxis (1.2 mg/kg for 3 consecutive days) failed to prevent ZIKV infection in rhesus macaque and did not alter ZIKV IgM antibody production. The secondary transfer of ivermectin from nonhuman primate blood to mosquito vectors at 3 days post-ZIKV inoculation and after the last dose of ivermectin administration showed no reduction in ZIKV replication in mosquitoes. However, mosquito survival rates were significantly (P <0.0001) lower after exposure to ivermectin, thereby potentially impacting ZIKV transmission through increased vector mortality. However, further investigation is needed to determine dosing regimens that may realize these effects in vivo.