Impacts of ivermectin mass drug administration for malaria control on smallholder pig health and productivity in Mozambique

Abstract

Abstract As part of a larger clinical trial testing ivermectin mass drug administration (iMDA) in humans and pigs for malaria vector control in Mozambique, this study evaluates ivermectin’s effects on gastrointestinal nematode burden, daily weight gain and economic outcomes in treated pigs over five months. Ivermectin (1% solution) was administered monthly for 3 months to pigs in the iMDA intervention arm at 300 mcg/kg. Households in intervention and control arms provided monthly data on pig health, management and income. Pigs were randomly selected for longitudinal fecal sampling and body measurements to estimate average daily gain (ADG). Compared to controls, treated pigs exhibited a 10.1% reduction in prevalence of strongyle eggs ( P = 0.004) and a 20.2% reduction in larvated strongyle eggs ( P = 0.004). Reductions in eggs per gram were 36.1% for strongyles ( P = 0.001), 33.0% for larvated strongyle eggs ( P = 0.029) and 26.7% for Ascaris suum ( P = 0.004). However, these reductions were modest and did not translate into significant improvements in ADG or other production outcomes. Ivermectin achieved <90% reduction in all nematodes in the fecal egg reduction count test, indicating reduced apparent efficacy under field conditions. Although this may suggest reduced drug efficacy, the epidemiological context, including high environmental contamination, scavenging behaviour and limited husbandry inputs, indicates that continuous reinfection and operational factors are plausible explanations. Overall, these results suggest that ivermectin delivered through iMDA can reduce parasite burden but is insufficient to improve pig productivity in high-transmission smallholder systems without complementary management and environmental interventions.