The impact of the termination of Lymphatic Filariasis mass drug administration on Soil-transmitted Helminth prevalence in school children in Malawi
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Background
Soil-transmitted helminths (STH) have been passively treated with the implementation of mass drug administration (MDA), with the drugs ivermectin and albendazole, against the parasitic disease, lymphatic filariasis (LF). In Malawi, LF MDA was administered to communities between 2008 and 2014. The aim of this analysis is to estimate the impact of LF MDA and its termination on STH prevalence in school aged children.
Methodology
School survey data of STH prevalence in Malawi were obtained through the ESPEN website. The surveys spanned the periods before (1998-2004), during (2012-2014) and after LF MDA (2015-2019). Bayesian mixed-effects models were fit to estimate the impact of LF MDA termination, and other STH risk factors, on the odds of infection as well as generate predictions of nationwide STH prevalence after LF MDA.
Principal findings
School children after the termination of LF MDA had a threefold increase in the odds of A. lumbricoides infection compared to school children during the implementation of LF MDA (Odds Ratio (OR): 3.4, 95% credible interval (CI): 1.99 – 5.94), despite ongoing STH preventive chemotherapy targeting school age children. In contrast, school children had lower odds of hookworm infection after LF MDA compared to during (OR: 0.5, 95% CI: 0.33 – 0.73). Mulanje district in the south has above 50% probability of exceeding 20% A. lumbricoides prevalence while the probability for exceeding 20% hookworm prevalence is below 50% nationwide.
Conclusions/significance
An overall resurgence in A. lumbricoides infections after LF MDA is identified in school children despite ongoing annual STH preventive chemotherapy. Monitoring of STH prevalence and infection intensity using high sensitivity diagnostics should be prioritised to surveil this resurgence and better delineate infection hotspots. A greater assessment of underlying factors would also further aid the identification of hotspots.
Author Summary
Soil-transmitted helminths (STH) are a group of parasitic worms that cause infections. They cause significant morbidity in children and women and the World Health Organisation (WHO) recommends the mass distribution of drugs to these populations to treat infections. In Malawi, distribution of albendazole to school age children to treat STH has been conducted annually since at least 2012. In the past, Malawi also distributed albendazole to whole communities to treat another parasitic disease, lymphatic filariasis (LF). The aim of this study was to investigate the impact of terminating LF treatment on STH prevalence in school children. We found that after mass LF treatment was stopped, school children had around three times the odds of infection for one species of STH, compared to school children during the time of LF treatment distribution. This indicates a resurgence in infection, despite ongoing STH treatment, after community-wide treatment against LF was stopped. To better understand the lack of community treatment and its impact, monitoring of STH prevalence and infection intensity with more sensitive diagnostics needs to be prioritised to avoid further resurgence of infection. An understanding of underlying factors, such as population movement or the potential emergence of drug resistance, would also help in identifying hotspots.
