‘Slash and clear’ vector control for onchocerciasis elimination and epilepsy prevention: a protocol of a cluster randomised trial in Cameroonian villages

Abstract

IntroductionOnchocerciasis, caused by the filarial nematode Onchocerca volvulus, remains endemic in Cameroon despite decades of community-directed treatment with ivermectin (CDTI). CDTI is often hampered by coendemicity with loiasis (another filariasis caused by Loa loa) in some areas. Strong epidemiological evidence suggests that O. volvulus infection increases the risk for onchocerciasis-associated epilepsy (OAE) among Cameroonian children. This highlights the urgent need to strengthen onchocerciasis elimination programmes in mesoendemic/hyperendemic areas. Novel alternative strategies, such as the ‘slash and clear’ (S&C) vector control method, may be required to complement ongoing CDTI to accelerate elimination of transmission. The short-term impact of S&C on the biting rates of the blackfly vectors has been demonstrated in other settings. However, its long-term effectiveness and impact on parasitological and serological markers of onchocerciasis transmission as well as on OAE are still unknown.Methods and analysisWe aim to assess the effectiveness of annual S&C interventions combined with CDTI in reducing onchocerciasis transmission and epilepsy incidence. Eight onchocerciasis-endemic villages located <5 km from the Mbam or Sanaga rivers will be randomised to two arms: four villages will receive yearly CDTI only for two consecutive years (Arm 1), while the other four villages will receive CDTI plus annual S&C for 2 years (Arm 2). Study outcomes (blackfly biting rates, infectivity rates and seroprevalence of onchocerciasis antibodies (Ov16 antibodies) in children, prevalence of microfilaridermia and epilepsy incidence) will be monitored prospectively and compared across study arms. We expect that S&C will have an added benefit over CDTI alone.Ethics and disseminationThe protocol has received ethical approval from the institutional review board of the Cameroon Baptist Convention Health Board (reference number: IRB2021-03) and has been registered with the Pan African Clinical Trials Registry. Findings will be disseminated at national and international levels via meetings and peer-reviewed publications.Trial registration numberPACTR202101751275357.

Usability, acceptability and cost of the SD BIOLINE Ov16 rapid diagnostic test for onchocerciasis surveillance in endemic communities in the middle belt of Ghana

“…In a formerly highly endemic area in the Mbam and Sanaga river valleys of Cameroon, Siewe Fodjo et al [40] found an Ov16 seropositivity of 47% (68/145) in Bilomo (Centre Region) and 52% (13/25) in Kelleng (Littoral Region) among children aged 7–10 years after >13 years of CDTI. A factor likely involved in the persistence of onchocerciasis in this area is the very high (and perennial) biting rates of the blackfly vectors, as documented in other localities of the Mbam and Sanaga river systems, both historically and recently [41,42]. As our study area was originally mesoendemic, and annual biting rates in the region were of the order of 3,000–4,000 per person [19], it would be advisable to update entomological studies in the Tain District and Wenchi Municipality of Ghana to better understand the potential contribution of blackfly abundance, species composition and transmission intensity to persistent infection.…”

“…Entomological studies should also be undertaken in the study area to assess infection levels in simuliid population samples. [41,42]. As our study area was originally mesoendemic, and annual biting rates in the region were of the order of 3,000-4,000 per person [19], it would be advisable to update entomological studies in the Tain District and Wenchi Municipality of Ghana to better understand the potential contribution of blackfly abundance, species composition and transmission intensity to persistent infection.…”

Community Perceptions of Blackfly Nuisance and Acceptability of the “Slash and Clear” Vector Control Approach in the Ntui Health District of Cameroon: A Qualitative Study

“…Our research team has been conducting a research project for the past three years, aiming to implement the “Slash and Clear” approach along segments of the longest river in Cameroon, the Sanaga River, and investigate community perceptions as well as the sustainability of this intervention [ 23 ]. Thus, the first phases of the project consisted of formative research, whereby qualitative studies were conducted to understand how the community experienced the blackfly nuisance and whether the “Slash and Clear” intervention was welcomed in the study villages.…”

Epidemiology of epilepsy and relationship with onchocerciasis prevalence in villages of the Ntui Health District of Cameroon

“…Although the Sanaga river (the longest river in Cameroon) also harbors several blackfly breeding sites which render the surrounding villages endemic for onchocerciasis as well as OAE [ 23 ], few studies have been done in villages along its banks. In a bid to identify breeding sites in the Sanaga river where vector control activities can be implemented to reduce onchocerciasis transmission and epilepsy prevalence/incidence, we initiated a project in selected villages along this river [ 24 ]. In the present paper, we report the baseline findings regarding the epilepsy situation in the study villages and how this relates to the onchocerciasis endemicity levels prior to implementing vector control measures.…”