Entomological assessment of the transmission following recrudescence of onchocerciasis in the Comoé Valley, Burkina Faso

Abstract

BackgroundOnchocerciasis, or river blindness, is a dermal filariasis caused by infection with the nematode parasite Onchocerca volvulus, transmitted to humans through the bites of blackflies of the genus Simulium. Despite the decade-long West African Regional Programme for the Elimination of Onchocerciasis, involving the mass administration of ivermectin to populations in endemic areas, recrudescence has occurred. An example is in the Cascades Region of south-west Burkina Faso where the resumption of transmission had resulted in infection prevalences of up to 70% in some villages. In 2011, a strategy for community-directed distribution of ivermectin (CDTI) was set up to respond to this worrying re-emergence.Here, we report on a study of Onchocerca spp. transmission in the affected area carried out from January to December 2012. Every month, host-seeking adult females of the S. damnosum complex were collected at sites on the River Comoé near the four villages (Bodadiougou, Bolibana, Badara Karaboro and Badara Dogossè) that had recorded the highest prevalences in 2010. Collected blackflies were dissected and infective larvae were identified using the O-150 PCR method.ResultsA total of 9114 S. damnosum (s.l.) adult females were collected, of which 5142 were parous (56.4%) and 78 (1.51%) were infective carrying a total of 137 infective larvae. The annual transmission potential (ATP) was calculated as 0, 30, 255 and 771 infective larvae/man/year in Badara Dogossè, Bolibana, Badara Karaboro and Bodadiougou, respectively. Transmission levels in the latter two are of particular concern as they were higher than 100 infective larvae/person/year, the designated minimum threshold required for elimination of severe pathology, including damage to vision.ConclusionsThese results confirm that recrudescence of onchocerciasis has occurred, and that transmission of O. volvulus was active at sites on the Comoé River in the Cascades region in 2012. In accordance with WHO recommendations, CDTI should be continued and the situation in the Cascades region should be closely monitored if further spread of this outbreak is to be avoided.Electronic supplementary materialThe online version of this article (10.1186/s13071-019-3290-5) contains supplementary material, which is available to authorized users.

Genomic Epidemiology in Filarial Nematodes: Transforming the Basis for Elimination Program Decisions

“…In the Comoé basin, retrospective analysis of recrudescence suggested that long-range vector movement was responsible, although immigration of infected people from outside the basin was not excluded. Ongoing transmission was confirmed via entomological assessments at 4/4 capture points (Koala et al, 2017;Koala et al, 2019). The second Burkina Faso report investigated microfilariaepositive individuals in the Upper Mouhoun, Nakambé , and Nazinon river basins and found all but 1 of the 31 infected individuals recently resided in neighboring Cô te d'Ivoire (Nikièma et al, 2018).…”

“…Data from Burkina Faso showed a significant delay between cessation of interventions and recrudescence (Koala et al, 2017;Koala et al, 2019), suggesting that the predicted time frames for recrudescence modeled by McCulloch et al (2017) are realistic. Such delays are not unexpected considering that parasite invasion may initiate transmission at a low level, and transmission takes time to become detectable.…”

“…Although the success of MDAi has driven the move from control to elimination of onchocerciasis, there are some areas in Africa in which many years of MDAi have reduced infection prevalence less than expected (i.e., less than transmission models predict) or where resumption of transmission has been reported following cessation of interventions (Kamga et al, 2016;Tekle et al, 2016;Koala et al, 2017;Bakajika et al, 2018;Komlan et al, 2018;Koala et al, 2019). Transmission models predict that the duration of interventions required to interrupt transmission is dependent on vector abundance (which determines the percentage of the population infected before interventions begin), and the treatment frequency and percentage of the population taking ivermectin (African Programme for Onchocerciasis Control/World Health Organization, 2010; Stolk et al, 2015).…”

Utility of theOnchocerca volvulusmitochondrial genome for delineation of parasite transmission zones

“…Once available and validated, and provided the geographically relevant population genetic data are 450 available, such a model will allow to quantitate the risk associated with stopping interventions in one 451 geographic area meeting WHO guideline criteria when 'neighbouring' areas do not. Recrudescence could be attributable in some areas to long-range migration of infected flies from Côte 459 d'Ivoire, although recrudescence due to undetected infections in the Comoé river valley was not excluded 460 (Koala et al, 2017;Koala et al, 2019). With the methods established here, analysis of parasites from 461…”

Data-driven modelling and spatial complexity supports heterogeneity-based integrative management for eliminating Simulium neavei-transmitted river blindness

“…Impacts of vector control were investigated by UOEP by measuring changes in the aggregate values of ABR in each focus. Typically, biting data from human landing catches (HLCs) carried out in 14 catching sites along the relevant river system in a focus during the 4-5 months pertaining to the major transmission season (at frequencies of 2 days per week) were used to make these focus-level ABR calculations using the calculation methods described in 69 .…”