Abstract
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 efficacious against headlice, and is also 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 (MDA) 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 μg/kg, livestock: 1% injectable 200 μg/kg) in 3 consecutive months during the rainy season. The control group received albendazole (humans only). Thirty-nine clusters (13 per arm) were randomly selected for the nested assessment of headlice prevalence. 1341 treated participants were followed up at least once, 1, 2 and 3 months and 382 untreated (ineligible) participants at 3 and 6 months after the first MDA round. Headlice diagnosis was determined by scalp examination. Logistic regression was used to identify risk factors for headlice at baseline, and to estimate the treatment effect at each time point. RESULTS: A total of 1309 participants were included in the main analysis assessing ivermectin MDA efficacy, and 1332 in the risk factor analysis. The baseline headlice prevalence was 11%. Risk factors included living with a household member with head itch [adjusted odds ratio (aOR) = 48.63, 95% confidence interval (CI): 28.7-82.3, P-value < 0.0001], being female (aOR = 2.25, 95% CI: 1.33-3.80, P-value < 0.01), and using surface water as the main water (aOR = 2.37, 95% CI: 1.12-5.33, P-value = 0.04). The treated population receiving ivermectin had significantly lower odds of having headlice at 3 months compared to those receiving albendazole (aOR = 0.19, 95% CI: 0.04-0.91, P-value = 0.04). There was no indirect effect on headlice among children ineligible for treatment. CONCLUSIONS: 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. TRIAL REGISTRATION: This study is registered with ClinicalTrials.gov (NCT04966702).