Evaluating the impact of alternative intervention strategies in accelerating onchocerciasis elimination in an area of persistent transmission in the West Region of Cameroon

Abstract

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 damnosum s.l. 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 a longer period, with a reduction of prevalence of 29.0% under AIS in 2017–2019 compared to 14.6% with IVM in 2011–2015; and 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, i.e., where migration of flies or humans to and from neighbouring areas is common. 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.

Acceptability of test and treat with doxycycline against Onchocerciasis in an area of persistent transmission in Massangam Health District, Cameroon

“…Programme staff expressed concern about timing between of ivermectin and TTd, citing a lack of clarity on how ivermectin will impact TTd. This resulted to testing in intervention 1 being less than three months since CDTi, suspected to have contributed to low detected infection level during intervention 1 compared to baseline (Intervention 1: 24%, n = 643, Table 2 vs baseline: 36%, n = 557) [ 16 , 18 ]. This prompted a catch-up round (intervention 2) where everyone was offered testing and results revealed a higher infection level than in round 1 (round 2 being 29%, n = 879, Table 2 ).…”

“…Implementing CDTi immediately after skin snip collection followed by doxycycline treatment to people with detected mf, would give beneficiaries immediate and sustained symptoms clearance [ 31 ]. It will also be more impactful by breaking the transmission cycle quicker as evident in the impact evaluation of these interventions and elsewhere [ 18 , 32 ]. There are some evidence that even though mf are still present for >12 months after doxycycline treatment, their ability to be transmitted is hindered [ 8 , 14 ].…”

“…After obtaining written informed consent and additional ascent for those younger than 18 years, eligible individuals—above the age of 8, not pregnant, not breast feeding and not having severe illness, not allergic to doxycycline—were invited to a fixed location for onchocerciasis screening (test) through skin snip biopsy [ 18 ]. Pregnancy was excluded by performing urinary dipstick test for all women of child-bearing age (>15 years) and only those showing a negative test were included.…”

“…This suggest persistent ongoing transmission and that the area is not on track to elimination despites nearly 20 years of uninterrupted annual CDTi with reported achievement of minimum programmatic coverage [ 16 ] (>80% therapeutic coverage) [ 15 , 17 ]. Responding to the high infection, we implemented ATS that included biannual CDTi, ground larviciding and test and treat with doxycycline (TTd) [ 18 – 20 ]. Unlike in the COUNTDOWN project [ 21 ] where each strategy was implemented separately, in Massangam all the strategies were delivered to the same focus/area ( Fig 1 ).…”

“…An impact evaluation of these interventions showed a significant and rapid reductions in mf prevalence (from 35.7% to 12.3%; p<0.001) and Community Microfilaria Load (CMFL), from 0.66 to 0.22 mf/ss in the focal communities over a two-year period. Detail report of the impact (effectiveness) of the whole ATS package is presented elsewhere [ 18 ]. This paper focuses on the acceptability of the TTd component.…”