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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.

Historically, the whole of Burkina Faso was considered to be endemic for onchocerciasis (except a small area in the far north of the country) with prevalence rates 60-80%, but all endemic areas were included in the World Health Organisation Onchocerciasis Control Programme, which operated a system of vector control by larviciding beginning in 1974. In Burkina Faso larviciding had been phased out by 1989 when it was considered that onchocerciasis had been reduced to levels below the transmission breakpoint (and any residual infections would disappear without further intervention). There was never any mass drug administration against onchocerciasis in Burkina Faso, except in the Bougouriba and Comoé river basins (from 1996 and 2011 to present respectively) because in each of these two areas there was a resurgence of infection, and in parts of the Nakambé River basin and Sissili River basin from 1992 to 1998. However, mass drug administration with ivermectin was also phased in across the whole country starting in 2000 using ivermectin against lymphatic filariasis and is currently being phased out (depending upon the epidemiological parameters). In this publication we report a new epidemiological survey for onchocerciasis which was carried out in 2014 in the Upper Mouhoun, Nakambé and Nazinon river basins in Burkina Faso to evaluate the prevalence and intensity of infection of onchocerciasis. A total of 11,195 people from 61 villages were examined across these three river basins, and onchocerciasis prevalence by skin-snip was below 5% in all villages, below 1% in 57 villages (93% of 61 villages) and zero in 47. In the 14 villages with positive skin snips, prevalence figures ranged from 0.31% to 3.50%. During the survey 31 infected individuals were found. All of them were Burkinabé, of whom 30 had a recent history of residence in Côte d'Ivoire (with a range of 0.5 to 73 microfilariae per skin-snip from two snips per person) and only one had no history of migration and presumably had an autochthonous infection (mean of 0.5 microfilariae per skin snip from two snips). According to parasitological indicators listed by the World Health Organization African Programme for Onchocerciasis Control in 2010, the situation for onchocerciasis was considered to be satisfactory in all three river basins and probably below the transmission threshold, in which case the disease should disappear naturally without the need for further intervention in the absence of continuing immigration. However, the results clearly indicate that infected persons coming from endemic zones of Côte d'Ivoire are settling in small communities which are otherwise nearly free from onchocerciasis in Burkina Faso. They are thus a source of continuing re-introduction of the parasite into the basins and could be a risk for the achievement of onchocerciasis elimination in all three basins. This would justify the continuation of periodic epidemiological surveys to monitor the possible recrudescence of the disease, and entomological (vector) surveys should be undert...

In West Africa, Aedes aegypti remains the major vector of dengue virus. Since 2013, dengue fever has been reemerging in Burkina Faso with annual outbreaks, thus becoming a major public health problem. Its control relies on vector control, which is unfortunately facing the problem of insecticide resistance. At the time of this study, although data on phenotypic resistance were available, information related to the metabolic resistance in Aedes populations from Burkina Faso remained very scarce. Here, we assessed the phenotypic and the metabolic resistance of Ae. aegypti populations sampled from the two main urban areas (Ouagadougou and Bobo-Dioulasso) of Burkina Faso. Insecticide susceptibility bioassays to chlorpyriphos-methyl 0.4%, bendiocarb 0.1% and deltamethrin 0.05% were performed on natural populations of Ae. aegypti using the WHO protocol. The activity of enzymes involved in the rapid detoxification of insecticides, especially non-specific esterases, oxidases (cytochrome P450) and glutathione-S-transferases, was measured on individual mosquitos. The mortality rates for deltamethrin 0.05% were low and ranged from 20.72% to 89.62% in the Bobo-Dioulasso and Ouagadougou sites, respectively. When bendiocarb 0.1% was tested, the mortality rates ranged from 7.73% to 71.23%. Interestingly, in the two urban areas, mosquitoes were found to be fully susceptible to chlorpyriphos-methyl 0.4%. Elevated activity of non-specific esterases and glutathione-S-transferases was reported, suggesting multiple resistance mechanisms involved in Ae. aegypti populations from Bobo-Dioulasso and Ouagadougou (including cytochrome P450). This update to the insecticide resistance status within Ae. aegypti populations in the two biggest cities is important to better plan dengue vectors control in the country and provides valuable information for improving vector control strategies in Burkina Faso, West Africa.

Introduction: Lymphatic filariasis (LF) and malaria are two vector-borne diseases which parasites can simultaneously infect human or mosquito. In Burkina Faso, studies mainly focused on the control of these diseases independently. Hence, there is a lack of information on their co-transmission of to both human and vector. The present study aimed at providing baseline data from endemic areas in Burkina Faso towards a successful integrated management of both diseases. Methods: The study was carried out in six sites distributed in the East, Center-East and South-West regions of Burkina Faso. Data were collected in August 2014 and September 2015. The infection rates in human and vector populations, vector diversity, trophic and resting behavior were investigated. To determine the disease prevalence nocturnal fingerprick blood sample and microscopic observations were performed. Vectors collected by human landing catches and pyrethrum spray collections. Biochemical and molecular analyses were performed to identify Anopheles gambiae sensu lato sibling species, and to determine vector infection rate and their blood meal origins. Results: Results indicate residual transmission of LF and malaria in human and vector populations. A low co-infection rate (<1%) with Wuchereria bancrofti and Plasmodium falciparum was noted in both human and mosquito. Anopheles gambiae s.l., An. funestus s.l. and An. nili were by order the main potential vectors encountered. It was in majority parous females and exhibited endophagic and exophagic behavior.

In Burkina Faso, onchocerciasis was no longer a public health problem when the WHO Onchocerciasis Control Programme in West Africa closed at the end in 2002. However, epidemiological surveillance carried out from November 2010 to February of 2011, showed a recrudescence of infection in the Cascades Region. This finding was made at a time when ivermectin, a drug recommended for the treatment of both onchocerciasis and lymphatic filariasis, had been distributed in this area since 2004 for the elimination of lymphatic filariasis. It was surprising that ivermectin distributed for treating lymphatic filariasis had not prevented the recrudescence of onchocerciasis. Faced with this situation, the aim of our study was to evaluate the effectiveness of ivermectin on the onchocerciasis parasite. The percentage reduction in microfilarial load after treatment with ivermectin was used as a proxy measure for assessing possible resistance. A cohort study was carried out with 130 individuals who had tested positive for microfilariae of Onchocerca volvulus in 2010 using microscopic examination of skin-snip biopsies from five endemic villages. Subjects were followed from July 2011 to June 2012. The microfilarial load of each individual was enumerated by skin-snip biopsy in 2010, prior to the first ivermectin treatment against onchocerciasis under community guidelines. All individuals received two ivermectin treatments six months apart. In 2012, the microfilarial loads were determined again, six months after the second round of ivermectin and the reductions in parasite loads were calculated to measure the impact of the drug. The percentage reduction of the microfilarial loads ranged from 87% to 98% in the villages. In all villages, there was a statistically significant difference between the average microfilarial loads in 2010 and 2012. The level of reduction of microfilarial loads suggests that ivermectin is effective against the recrudescent population of O. volvulus in Cascades Region of Burkina Faso. Further investigations would be necessary to determine the causes of the recrudescence of onchocerciasis. (For French language abstract, see S1 Alternative Language Abstract—Translation of the Abstract into French by the authors.)

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