The impact of the termination of Lymphatic Filariasis mass drug administration on Soil-transmitted Helminth prevalence in school children in Malawi

BACKGROUND: Soil-transmitted helminths (STH) have been passively targeted through 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 was to estimate the impact of LF MDA and its termination on STH prevalence in school aged children (SAC). 

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 fitted 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 during and after LF MDA. 

PRINCIPAL FINDINGS: SAC after the termination of LF MDA had 1.8 times greater odds of A. lumbricoides infection compared to SAC during the implementation of LF MDA (95% credible interval (CI): 1.03 - 3.35), despite ongoing STH preventive chemotherapy (PC) targeting SAC. Predictions indicate majority of districts increased in their probability of exceeding 2% A. lumbricoides prevalence in SAC after the termination of LF MDA, with Chitipa, Mulanje and Nsanje districts estimated to have > 80% probability of exceeding 2% prevalence. 

CONCLUSIONS/SIGNIFICANCE: An overall resurgence in A. lumbricoides infections after LF MDA was estimated in SAC, despite ongoing annual STH PC. This suggests STH PC could not sustain the prevalence levels achieved in SAC under community-wide LF MDA. The potential role of drug resistance in this resurgence calls for urgent investigation. Understanding how this resurgence corresponds to prevalence of moderate and heavy infections should be a priority for future research.