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

## TL;DR

Ending a mass drug program for one parasitic disease in Malawi led to a rise in another parasitic infection among school children, despite ongoing treatment efforts.

## Contribution

This study is the first to show a resurgence of soil-transmitted helminths after ending community-wide drug administration for lymphatic filariasis.

## Key findings

- School children had 1.8 times higher odds of A. lumbricoides infection after LF MDA termination.
- Most districts increased their probability of exceeding 2% A. lumbricoides prevalence post-MDA.
- Ongoing STH PC could not maintain the low prevalence levels achieved during community-wide LF MDA.

## Abstract

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).

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.

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.

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.

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 as preventive chemotherapy (PC). In Malawi, distribution of albendazole to school age children (SAC) against STH has been conducted annually since at least 2012, as STH PC. In the past, Malawi also conducted mass drug administration (MDA) with albendazole and ivermectin to whole communities against another parasitic disease, lymphatic filariasis (LF). The aim of this study was to investigate the impact of terminating LF MDA on STH prevalence in SAC. We found that after the end of the programme, SAC had around 1.8 times the odds of infection for one species of STH, compared to SAC during the time of LF MDA. This indicates a resurgence in infection, despite ongoing STH PC, after the end of LF MDA and suggests STH PC could not sustain prevalence levels achieved under LF MDA. To better understand the lack of community-wide distribution and its impact, monitoring of STH prevalence and infection intensity with more sensitive diagnostics needs to be prioritised to avoid further resurgence of infection.