Monitoring Aedes populations for arboviruses, Wolbachia, insecticide resistance and its mechanisms in various agroecosystems in Benin.

Aedes mosquitoes are the main vectors of arboviruses in Benin. Cases of dengue have been reported in Benin with all four serotypes of the virus actively circulating in this region. Some agricultural settings are known to harbor Aedes vectors responsible for the transmission of arboviruses. The massive use of certain insecticides in agricultural settings has probably contributed to insecticide resistance in these vectors. In Benin, the susceptibility of arbovirus vectors to insecticides is poorly studied. In addition, the distribution of Wolbachia spp., which is used against some arboviruses is unknown. Moreover, there is limited information regarding the vectors responsible for the transmission of arboviruses in Benin. This present study monitored the species composition, arboviruses, and Wolbachia symbiont status, as well as the phenotypic and molecular insecticide resistance profile of Aedes populations from three agroecosystems in Benin. Aedes species identification was performed morphologically and confirmed using qPCR. (RT)-qPCR assay was applied for monitoring the presence of DENV, CHIKV, ZIKV, and WNV pathogens as well as for naturally occurring Wolbachia symbionts. Insecticide resistance was assessed phenotypically, by permethrin (0.75%) exposure of Adults (F0) using World Health Organization (WHO) bioassay protocols, and at the molecular level, using TaqMan (RT)-qPCR assays for assessing knock-down resistance (kdr) mutations (F1534C, V1016G/I, and S989P) and the expression levels of eight detoxification genes (P450s from the CYP9 and CYP6 families, carboxylesterases and glutathione-S-transferases). Aedes aegypti (Ae. aegypti) mosquitoes were the most abundant (93.9%) in the three agroecosystems studied, followed by Aedes albopictus (Ae. albopictus) mosquitoes (6.1%). No arboviruses were detected in the study's mosquito populations. Naturally occurring Wolbachia symbionts were present in 7 pools out of 15 pools tested. This could influence the effectiveness of vector control strategies based on exogenously introduced Wolbachia, all present in the three agroecosystems. Full susceptibility to permethrin was observed in all tested populations of Ae. albopictus. On the contrary, Ae. aegypti were found to be resistant in all three agroecosystem sites except for banana plantation sites, where full susceptibility was observed. Molecular analysis revealed that individual target site resistance kdr mutations F1534C and V1016G/I were detected in most Ae. aegypti populations. Additionally, double mutant (F1534C + V1016G/I) mosquitoes were found in some populations, and in one case, triple mutant (F1534C + V1016G/I + S989P) mosquitoes were detected. Metabolic resistance, as reflected by overexpression of three P450 genes (CYP6BB2, CYP9J26, and CYP9J32), was also detected in Ae. aegypti mosquitoes. Our study provides information that could be used to strategize future vector control strategies and highlights the importance of continuing vector surveillance. Future studies should assess the effect of piperonyl butoxide (PBO) on metabolic resistance and identify the different strains of Wolbachia spp., to choose the best vector control strategies in Benin.

Chikungunya virus infection prevalence in Africa: a contemporaneous systematic review and meta-analysis.

OBJECTIVES: The (re)emergence of chikungunya virus (CHIKV) in Africa requires better knowledge on the epidemiology of CHIKV infection in the continent for efficient public health strategies. We aimed to describe the epidemiology of CHIKV infection in Africa, a neglected tropical disease (NTD). STUDY DESIGN: This was a systematic review with meta-analysis of studies reporting CHIKV infection prevalence. We searched Embase, PubMed, Africa Journal Online and Global Index Medicus to identify observational studies published from January 2000 to September 2017. METHODS: We used a random-effect model to pool the prevalence of CHIKV infections reported with their 95% confidence interval (CI). Heterogeneity was assessed via the Chi-squared test on Cochran's Q statistic. Review registration is in PROSPERO CRD42017080395. RESULTS: A total of 39 studies (37,881 participants; 18 countries) were included. No study was reported from Southern Africa. Thirty-two (82.0%), seven (18.0%) and no studies had low, moderate and high risk of bias, respectively. Outside outbreak periods, the pooled immunoglobulin M (IgM) and immunoglobulin G (IgG) seroprevalence was 9.7% (95% CI 3.0-19.6; 16 studies) and 16.4% (95% CI 9.1-25.2; 23 studies), respectively. The IgM seroprevalence was lower in Northern Africa, and there was no difference for IgG prevalence across regions in Africa. The IgM and IgG seroprevalences were not different between acute and non-acute febrile participants. The seroprevalence was not associated with GPS coordinates (latitude, longitude and altitude). CONCLUSIONS: Although considered a NTD, we find high prevalence of CHIKV infection in Africa. As such, chikungunya fever should deserve more attention from healthcare providers, researchers, policymakers and stakeholders from many sectors.

Seroepidemiological Studies of Arboviruses in Africa.

The literature on sero-epidemiological studies of flaviviral infections in the African continent is quite scarce. Much of the viral epidemiology studies have been focussing on diseases such as HIV/AIDS because of their sheer magnitude and impact on the lives of people in the various affected countries. Increasingly disease outbreaks caused by arboviruses such as the recent cases of chikungunya virus, dengue virus and yellow fever virus have prompted renewed interest in studying these viruses. International agencies from the US, several EU nations and China are starting to build collaborations to build capacity in many African countries together with established institutions to conduct these studies. The Tofo Advanced Study Week (TASW) was established to bring the best scientists from the world to the tiny seaside town of Praia do Tofo to rub shoulders with African virologists and discuss cutting-edge science and listen to the work of researchers in the field. In 2015 the 1st TASW focussed on Ebola virus. The collections of abstracts from participants at the 2nd TASW which focused on Dengue and Zika virus as well as presentations on other arboviruses are collated in this chapter.

[African Programme for Onchocerdasis Control (APOC): Onchocerca Simulium squamosum in two regions in the Republic of Cameroon]. / Programme africain de lutte contre l'onchocercose (APOC): intensité de la transmission d'Onchocerca volvulus par Simulium squamosum dans deux régions de la République du Cameroun.

In 1998, the African Programme for Onchocerciasis Control (APOC) decided to launch a long-term impact assessment of its operations. This paper reports the baseline entomological data collected throughout a whole year in two sites of Cameroon (Kahn and Bolo). The Simulium populations of the two study sites were characterized by parous rates of 7.2% and 33.5% respectively and infectivity by O. volvulus of 31 and 190 infective larvae per 1000 parous flies respectively The Annual Transmission Potentials (ATP) were respectively 523 and 9972 infective larvae per man and per year in Kahn and in Bolo. The Simulium populations studied in both sites, even though the ATP in Kahn is 19 times lower than that of Bolo, showed a pattern of an onchocerciasis hyperendemic zone in terms of vector capacities and entomological indices.

Loiasis: the individual factors associated with the presence of microfilaraemia.

No microfilariae are detectable in a significant percentage of those infected with the filarial worm Loa loa. While the probability of an infected individual becoming microfilaraemic is known to increase with age, the mechanisms underlying this trend are not well understood. Epidemiological data from an endemic village in central Cameroon were therefore explored, in an attempt to determine if, after taking into account any history of filaricidal treatment, the presence of Loa microfilaraemia in an individual was related to his/her gender, age, and/or exposure to the human-infective larvae of the parasite. An index of exposure, based on the monthly transmission potentials of the Chrysops in each of the main types of vegetation in a village and on the activity schedule of each inhabitant of the village, was developed. The results of the data analysis confirm that the acquisition of microfilaraemia is gender-dependent (males generally being more likely to be microfilaraemic than females), and indicate that, in males, a high level of exposure to infective larvae determines the shift from amicrofilaraemic to microfilaraemic status. They also indicate that filaricidal treatments have a long-lasting suppressive effect on Loa microfilaraemia, an observation that may have important implications for any strategy to limit the risk of Loa-associated encephalopathy following ivermectin treatment.

Experimental studies on the transmission of Onchocerca volvulus by its vector in the Sanaga valley (Cameroon): Simulium squamosum B. Intake of microfilariae and their migration to the haemocoel of the vector.

As large-scale ivermectin distribution is becoming the mainstay of onchocerciasis control in Africa, the issue of its impact on local transmission is increasing in importance. The vector competence of Simulium squamosum B in the severe focus of the Sanaga valley, Cameroon, was therefore investigated, by feeding 1320 flies on 14 carriers of Onchocerca volvulus microfilariae (mff). The results enabled the relationships between skin microfilarial load, microfilarial intake by the flies, the proportion and mean number of ingested mff that succeed in reaching the fly's haemocoel, and the frequency distribution of the ingested mff to be described, as functions of time post-engorgement (p.e.) and parasite density (while taking account of possible measurement error in the predictor variable). The proportion of flies with haemocoelic mff and the mean number of mff/fly increased up to 3 h p.e. The proportion of flies with ingested mff was non-linearly related to mean intake, via the negative-binomial distribution, with the overdispersion parameter k best described as an increasing (power) function of the mean. Approximately one in every three ingested mff escaped imprisonment by the peritrophic matrix, irrespective of the skin microfilarial load or the intake of mff. The relationship between successful and input mff is nearly linear (indicating proportionality) in S. squamosum B. These results are compared with those from O. volvulus-S. damnosum s.l. combinations in other West African foci.

[Entomologic study of loaiasis transmission in the Lekie area (Cameroon)]. / Etude entomologique sur la transmission de la loase dans de département de la Lékié (Cameroun).

A number of cases of Loa encephalopathy have been recorded after ivermectin treatment in the Lekie Division, an area of degraded forest located in central Cameroon. An entomological study was carried out in a village of this region between May 1999 and April 2000 to determine whether the high microfilarial loads of Loa found in the population, which can exceed 10,000 microfilariae per ml of blood, were related to high densities of vector populations. The Chrysops collected at 10 catching stations, using hand nets, by persons standing by a wood fire, were dissected to evaluate their level of infection with Loa. The vectorial densities were three-fold higher in the forest stations than in those located near the habitations (2307 and 725 bites per man per year, respectively). These values are lower than those reported from similar studies in Cameroon, Congo and Gabon. Measurement of Chrysops densities does not seem to be an appropriate tool to evaluate the level of endemicity of loiasis, and to delineate the areas where there is a risk of post-ivermectin Loa encephalopathies.

Density and dispersal of the loaiasis vector Chrysops dimidiata in southern Cameroon.

By mark-release-recapture experiments, we assessed the density of loaisis vectors, Chrysops dimidiata Wulp plus some Chrysops silacea Austen (Diptera: Tabanidae) and estimated their range of flight in the secondary forest of southern Cameroon. In 1993, the release point was at the centre of the study area and recapture points were at 1,100 m radius. In 1994, releases were on the periphery of the study area and recapture sites were 400-8,000 m from the release points. Results were concordant and showed Chrysops female densities of 785-3,682 flies/ km2. The theoretical flight range was < 6,000 m, with a maximum distance of 4,500 m observed. These results are considered promising for the use of vector control methods against loaiasis.

Impact of repeated large scale ivermectin treatments on the transmission of Loa loa.

We have studied the impact of large-scale treatment with ivermectin on the transmission of loiasis in a forest village in south Cameroon where loiasis was highly endemic, with a prevalence of 30%. After one year of parasitological and entomological surveillance without treatment, all consenting residents aged > 5 years received ivermectin 200 micrograms/kg every 3 months. For ethical reasons, treatment was interrupted after 2 years, but parasitological and entomological surveillance continued for 18 months after the end of treatment. The prevalence of loiasis was reduced to < 10% and the mean microfilaraemia decreased by 90% in 2 years. The prevalence and average intensity of infection remained stable during the 18 months after treatment ended. Two vector species were identified, Chrysops dimidiata (representing about 90% of the fly population) and C. silacea. The infection rate (all stages) in Chrysops decreased by 75% and the infective rate (percentage of Chrysops harbouring third-stage larvae of Loa loa in the head) decreased by 85% in C. dimidiata and became zero in C. silacea. After the end of treatment, the infection and infective rates increased gradually. Large-scale treatment seemed an efficient method for the control of L. loa transmission provided high drug coverage was achieved. Nevertheless, because of the high risk of adverse effects when using the current microfilaricidal drugs, such a strategy remains unacceptable.