Collateral benefits of ivermectin MDA designed for malaria against headlice in Mopeia, Mozambique: a cluster randomised controlled trial

Background Headlice are prevalent worldwide, with a higher burden in rural, lower-middle income settings. They can cause intense itchiness, discomfort, and secondary bacterial infections with potentially serious consequences. Ivermectin is known to be efficacious against headlice, and is also currently being evaluated as a malaria vector control tool. In this study, we explored risk factors for headlice, and assessed the efficacy of ivermectin mass drug administration designed for malaria against headlice. Methods We conducted an open-label, assessor-blind, cluster-randomized controlled trial in Mopeia, Mozambique. A single dose of ivermectin was given monthly to eligible humans or humans and livestock (humans: 400 ug/kg, livestock: 1% injectable 200 ug/kg) in 3 consecutive months during the rainy season. The control group received albendazole (humans only). 39 clusters (13 per arm) were randomly selected for the nested assessment of headlice prevalence. 1,341 treated participants were followed up at, 1, 2 and 3 months and 382 untreated (ineligible) participants at 3 and 6 months after baseline. Headlice diagnosis was determined by examination of the scalp. Logistic regression was used to identify risk factors for headlice at baseline, and to estimate the treatment effect at each time point. This study is registered with ClinicalTrials.gov (NCT04966702). Results The baseline prevalence of headlice was 11%. Risk factors included living with a household member with head itch, being female, and living with poor water and sanitation facilities. The treated population receiving ivermectin had significantly lower odds of having headlice at 3 months compared to those receiving albendazole (aOR 0.22 95%CI 0.05–0.89). There was no indirect effect on headlice among ineligible children. Conclusion In a highly endemic setting, mass drug administration with ivermectin significantly reduces headlice infestation prevalence among those who receive the drug for three sequential months. The lack of effect among untreated, ineligible children implies that additional interventions would be needed to interrupt local transmission.