Evaluating the impact of alternative intervention strategies in accelerating onchocerciasis elimination in an area of persistent transmission in the West Region of Cameroon
Authors: Atekem Kareen , Dixon Ruth , Wilhelm Aude , Biholong Benjamin , Oye Joseph , Djeunga Hugues Nana , Nwane Philippe , Ayisi Franklin , Boakye Daniel , Kamgno Joseph , Schmidt Elena , Nditanchou Rogers , Senyonjo Laura 
Published: June 2022

Background

Alternative strategies are recommended to accelerate onchocerciasis elimination in problematic areas including areas where annual ivermectin (IVM) distributions are unable to interrupt transmission. The aim of this study was to accelerate progress towards elimination in the Massangam health district, West Region of Cameroon where impact evaluations demonstrated ongoing transmission of onchocerciasis infection and high microfilaria (mf) prevalence despite more than 20 years of annual IVM distribution.

Methodology/Principal findings

Parasitological, entomological, and breeding site surveys were conducted in 2015 delineating a focus of high transmission and identified three communities with high mf prevalence. Individuals in these communities were screened for mf yearly for a period of two years and those positive treated each year with doxycycline 100mg daily for five weeks. In addition, surrounding communities were given biannual IVM. Temephos-based applications were performed once a week for 10 consecutive weeks on Simulium breeding sites. Parasitological and entomological assessments were conducted after two years of implementation and findings compared with 2015 baseline. Alternative strategies accelerated progress towards elimination through a significant mf reduction (χ2: 40.1; p<0.001) from 35.7% (95%CI: 29.0 -42.8) to 12.3% (95%CI: 9.0 - 16.4). Reductions were furthermore recorded over longer time period, with a reduction of mf prevalence by 23.2% following the two years of alternative strategies compared to 20.3% reduction over 15 years of treatment with IVM (1996-2011). Entomological assessment demonstrates that transmission is still ongoing despite the reduction in mf which is expected in an environment with complex breeding sites and open transmission zones.

Conclusion/Significance

This study provides evidence that alternative strategies are feasible and effective and should be considered in areas where transmission is sustained throughout long term uninterrupted MDA with IVM. However, there is need to consider wider transmission zones, and further explore optimal timing of larviciding with treatment to impact transmission.

Author summary

Elimination of onchocerciasis has showed to be possible when ivermectin (IVM) is given continuously every year for about 15-17 years. However, areas where continuous IVM distribution has not achieved this objective, alternative methods are needed. Massangam health district in Cameroon is one of such areas that IVM treatment has not stopped the spread of the disease despite more than 20 years of annual distribution. This study aimed to fast-track elimination through alternative intervention strategies (AIS). This included testing and treating those having onchocerciasis with doxycycline in communities where the infection was high, giving IVM twice a year to surrounding community members and reducing the flies that carry the worms by pouring chemical in river sites having fly larvae once a week for 10 weeks. The effect of these activities was measured and compared with previous data. The AIS significantly reduced percentage of those having the disease from 35.7% to 12.3%. A 23.2% reduction was also observed with two years of AIS compared with 20.3% reduction with IVM over 15 years. Thus, AIS are practical and useful and should be considered in areas where IVM has not successfully stopped the spread of onchocerciasis.