# Rebound in prevalence and intensity of Onchocerca volvulus infection five years after cessation of alternative treatment strategies in the Massangam Health District, West Region, Cameroon: need for coordinated and sustained efforts

## TL;DR

Five years after stopping alternative treatments for onchocerciasis in Cameroon, infection rates rebounded, showing the need for sustained and coordinated efforts to eliminate the disease.

## Contribution

This study demonstrates the importance of sustained and coordinated control efforts beyond health district levels to prevent the resurgence of onchocerciasis.

## Key findings

- The overall prevalence of Onchocerca volvulus infection was 18.7% five years after stopping alternative treatments.
- Infection rates were significantly higher in Mankakoun and Makouopsap compared to Njinja-Njingouet.
- Parasitological indicators increased significantly in all three communities after the cessation of alternative strategies.

## Abstract

The control of onchocerciasis currently relies on yearly distribution of ivermectin to at-risk populations. To tackle onchocerciasis in areas of high transmission (so-called hotspots) and achieve elimination of transmission, several complementary/alternative strategies (biannual ivermectin, doxycycline-based test-and-treat and vector control) were implemented in Massangam Health District (HD) in Cameroon, following World Health Organization (WHO) guidelines. A short-term impact evaluation revealed significant reductions in the endemicity levels in three focal hotspot communities (Makouopsap, Mankakoun, and Njinja-Njingouet). This study aimed to assess the situation of onchocerciasis in the focal hotspot communities five years after the cessation of the short pilot implementation of Alternative Treatment Strategies (ATS).

A quantitative cross-sectional survey was conducted in December 2023 in three focal hotspot communities of the Massangam Health District. Participants underwent a comprehensive assessment including parasitological examination (skin snipping) to establish Onchocerca volvulus microfilaridermia.

The overall prevalence of O. volvulus infection in the three focal communities was 18.7% (95% confidence interval CI: 14.1-24.3), significantly higher in the Mankakoun (30.8%) and Makouopsap (24.0%) communities compared to the Njinja-Njingouet community (7.0%) (p = 0.001). The intensity of infection was 3.136 (standard deviation, SD: 19.3099) mf/ss, ranging from 5.218 mf/ss (Mankakoun community) to 2.840 mf/ss (Njinja-Njingouet community). Parasitological indicators significantly increased five years after the cessation of ATS in all three focal communities (p = 0.0409).

These findings indicate a rebound in onchocerciasis transmission and underscore the need for coordinated and sustained efforts, implemented at the scale of a transmission zone per WHO recommendations, to achieve elimination goals.

Despite significant progress in controlling onchocerciasis through mass drug administration (MDA) with ivermectin, transmission persists in certain context despite uninterrupted efforts. To accelerate the elimination of infection, a package of alternative and complementary treatment strategies (ATS) was piloted in an area of higher transmission of onchocerciasis (Massangam Health District, West Region, Cameroon), resulting in a significant decrease in disease burden. We conducted a cross-sectional survey in three sentinel communities of the Massangam Health District five years after cessation of ATS. Our findings revealed a rebound of Onchocerca volvulus infection in the sentinel communities, suggesting a local rebound in infection consecutive to the fact that the area was yet to be cleared from infection, and/or the reintroduction of parasites from neighbouring health districts where such elimination effort (ATS) was not implemented. These findings underscore the urgent need for sustained (as long as needed to reach interruption of transmission indicators) and coordinated (in a transmission zone rather than at health district level) control efforts, especially those with proven impact such as test-and-treat with doxycycline or semi-annual ivermectin mass distribution, to achieve the WHO’s elimination goals.