Impact of ivermectin mass drug administration on burden of soil-transmitted helminths in onchocerciasis control and elimination programs, Yeki district, southwest Ethiopia

Community-directed treatment with ivermectin (CDTi) is the primary strategy employed to control and eliminate human onchocerciasis in Ethiopia. After long-term mass distribution for onchocerciasis, ivermectin is expected to have additional benefits beyond the envisioned targets by reducing the burden of other co-endemic parasitic infections as to STHs. To date, studies focused on the collateral impact of CDTi on STH in Ethiopia are scanty. Two community-based cross-sectional surveys (baseline in 1997 and post-CDTi in 2017) were conducted to evaluate the impact of long-term CDTi employed to control and eliminate onchocerciasis on the burden of STH infections in Yeki district of southwest Ethiopia. Stool samples were collected and examined using Ritchie`s concentration and Kato-Katz techniques in the baseline and current study, respectively. Overall, 188(38.3%, 95% Confidence interval (CI) 34.1–42.7%) individuals were positive at least for any of the STH species from 491 study participants in the post-CDTi. The prevalence of A. lumbricoides, hookworms, and T. trichiura was 11.2% (95% CI 8.7–14.3%), 16.3% (95% CI 13.3–19.8%), and 29.9% (95% CI 26.1–34.1%), respectively. Individuals aged 5–9 years had a significantly higher prevalence of A. lumbricoides (Adjusted odds ratio (AOR) 6.5, 95% CI 1.7–25.4), T. trichuria (AOR 8, 95% CI 2.6–25.1), and any STH infection (AOR 5, 95% CI 1.7–14.7) than those of ≥ 51 years. Also, significantly higher prevalences of T. trichuria infection were observed in individuals aged 10–14 years (AOR 4.1, 95% CI 1.7–9.9), 15–20 years (AOR 3.1, 95% CI 1.2–8.1), 21–30 years (AOR 2.4, 95% CI 1.1–5.5), and 31–40 years (AOR 3.2, 95% CI 1.3–7.5) compared with those of ≥ 51 years. The prevalence of A. lumbricoides was significantly higher in males (AOR 0.5, 95% CI 0.3–0.9). Of the 491 study participants, only data from 400 individuals who had not been involved in a mass drug administration (MDA) with other STH anthelmintics were considered in the comparative analysis. Before CDTi, the prevalence of A. lumbricoides, T. trichiura, hookworm, and any STH infection was 47.1% (95% CI 41.6–52.7%), 3.3% (95% CI 1.8–5.9%), 37.9% (95% CI 32.7–43.5%), and 58.8% (95% CI 53.2–64.1%), respectively. Long-term CDTi considerably reduced the prevalences of A. lumbricoides and hookworm by 76.2% and 56.9%, respectively (p < 0.001). Nonetheless, CDTi did not affect the prevalence of T. trichiura infection and, in contrast, it was significantly higher in the current study (P < 0.001). Overall post-CDTi prevalence of any STH infection was considerably lower than reported in the baseline (p < 0.001). It is evidenced that long-term CDTi for onchocerciasis control and elimination had additional benefits by reducing the prevalence of STH infections specifically of A. lumbricoides and hookworm, but had no impact on infections with T. trichuria. Our finding of additional health benefits of large-scale ivermectin administration taking it will aid to increase positive engagement and sustain participation of communities during MDA campaigns, and strengthen governmental and non-governmental organizations (NGOs) support for the undergoing national onchocerciasis elimination program.