Investigation of mechanisms of bendiocarb resistance in Anopheles gambiae populations from the city of Yaoundé, Cameroon

BACKGROUND Resistance to the carbamate insecticide bendiocarb is emerging in Anopheles gambiae populations from the city of Yaoundé in Cameroon. However, the molecular basis of this resistance remains uncharacterized. The present study objective is to investigate mechanisms promoting resistance to bendiocarb in An. gambiae populations from Yaoundé. METHODS The level of susceptibility of An. gambiae s.l. to bendiocarb 0.1 % was assessed from 2010 to 2013 using bioassays. Mosquitoes resistant to bendiocarb, unexposed and susceptible mosquitoes were screened for the presence of the Ace-1(R) mutation using TaqMan assays. Microarray analyses were performed to assess the pattern of genes differentially expressed between resistant, unexposed and susceptible. RESULTS Bendiocarb resistance was more prevalent in mosquitoes originating from cultivated sites compared to those from polluted and unpolluted sites. Both An. gambiae and Anopheles coluzzii were found to display resistance to bendiocarb. No G119S mutation was detected suggesting that resistance was mainly metabolic. Microarray analysis revealed the over-expression of several cytochrome P450 s genes including cyp6z3, cyp6z1, cyp12f2, cyp6m3 and cyp6p4. Gene ontology (GO) enrichment analysis supported the detoxification role of cytochrome P450 s with several GO terms associated with P450 activity significantly enriched in resistant samples. Other detoxification genes included UDP-glucosyl transferases, glutathione-S transferases and ABC transporters. CONCLUSION The study highlights the probable implication of metabolic mechanisms in bendiocarb resistance in An. gambiae populations from Yaoundé and stresses the need for further studies leading to functional validation of detoxification genes involved in this resistance

Plasmodium falciparum Produce Lower Infection Intensities in Local versus Foreign Anopheles gambiae Populations

Both Plasmodium falciparum and Anopheles gambiae show great diversity in Africa, in their own genetic makeup and population dynamics. The genetics of the individual mosquito and parasite are known to play a role in determining the outcome of infection in the vector, but whether differences in infection phenotype vary between populations remains to be investigated. Here we established two A. gambiae s.s. M molecular form colonies from Cameroon and Burkina Faso, representing a local and a foreign population for each of the geographical sites. Experimental infections of both colonies were conducted in Cameroon and Burkina Faso using local wild P. falciparum, giving a sympatric and allopatric vector-parasite combination in each site. Infection phenotype was determined in terms of oocyst prevalence and intensity for at least nine infections for each vector-parasite combination. Sympatric infections were found to produce 25% fewer oocysts per midgut than allopatric infections, while prevalence was not affected by local/foreign interactions. The reduction in oocyst numbers in sympatric couples may be the result of evolutionary processes where the mosquito populations have locally adapted to their parasite populations. Future research on vector-parasite interactions must take into account the geographic scale of adaptation revealed here by conducting experiments in natural sympatric populations to give epidemiologically meaningful results

Rapid evolution of pyrethroid resistance prevalence in Anopheles gambiae populations from the cities of Douala and Yaoundé (Cameroon)

Background The adaptation of malaria vectors to urban areas is becoming a serious challenge for malaria control. The study presents the evolution of pyrethroid resistance in mosquito populations from the cities of Douala and Yaoundé between 2010 and 2013. Methods Susceptibility tests to permethrin and deltamethrin were carried out with two- to four-day old unfed Anopheles gambiae sensu lato adults raised from larvae collected from the field. Mosquitoes resistant to permethrin and deltamethrin and control were screened to detect the presence of the kdr alleles using the TaqMan assays. Mosquitoes belonging to the An. gambiae complex were subjected to PCR assays designed for species and molecular forms identifications. The genomic region containing the upstream of intron-1 of the voltage-gated sodium channel was sequenced and compared between mosquitoes originating from different breeding habitats. Results Anopheles gambiae s.l. specimens collected from the city of Douala were all Anopheles coluzzii. In Yaoundé, both An. gambiae and An. coluzzii were recorded. A rapid decrease of mosquito mortality to permethrin and deltamethrin was recorded between 2010 and 2013 in the two cities. The mortality rate varied from 80.3 to 22.3% and 94.4 to 59.7% for permethrin and deltamethrin, respectively. Both kdr alleles L1014F and L1014S were recorded. The frequency of kdr alleles increased rapidly over the study period, varying from 44 to 88.9% in Yaoundé and from 68 to 81% in Douala. The sequencing of a 1,228 bp region of intro-1 of the voltage-gated sodium channel revealed the presence of five different haplotypes. A high number of these haplotypes were recorded in An. coluzzii samples. No evidence for a recent selective sweep on intron-1 sequence within samples originating from different breeding habitat was detected using Fu’s and Tajima Fs statistics. Conclusion The present study supports rapid evolution of pyrethroid resistance in vector populations from the cities of Douala and Yaoundé and calls for immediate action to fight against the increasing prevalence of pyrethroid-resistant mosquitoes

Larval habitats and susceptibility of malaria vectors to insecticides in semi-urban and rural localities of the Coast-Cameroon region: preliminary data

Le choix d’une stratégie appropriée de lutte anti-paludique dans un faciès éco-climatique donné requiert une bonne connaissance de l’écologie des vecteurs, notamment la distribution spatiale et la productivité des gîtes larvaires, et de leur niveau de sensibilité aux insecticides. La présente étude cartographie, caractérise les gîtes de ponte des moustiques et évalue la susceptibilité aux insecticides des vecteurs de paludisme à Banya II et Bodiman, deux localités l’une sub-urbaine et l’autre rurale, de la région du littoral camerounais. Les enquêtes sur le terrain ont été menées en mai 2015. Les gîtes de moustiques ont été géo-réferencés. Pour chaque gîte, les larves ont été prélevées puis élevées et les paramètres physico-chimiques mesurés in situ. La sensibilité des vecteurs au Dichlorodiphényltrichloroéthane (DDT), à la Deltaméthrine et à la Perméthrine a été évaluée sur les anophèles issus de l’élevage des larves. Une diversité de gîtes a été identifiée dans les sites d’étude (mares, cours d’eau, caniveaux, pneus, emballages-plastiques, récipients de réserve d’eau, récipients abandonnés, trous de papayer, trous de bambou). Cependant, Anopheles gambiae s.l., l’espèce la plus abondante à Banya II a été plus fréquente dans les mares, alors que Culex poicilipes, l’espèce la plus abondante à Bodiman a été majoritairement collectée dans des récipients abandonnés. Les deux catégories de gîtes avaient respectivement une conductivité électrique de 167,5 [16,9-305] et 170,43 [11,6-461] µs/cm ; une salinité de 90,5 [23,5-157] et 94,6[15-240] g/l ; un total de solides dissous (TDS) de 119,6 [20,6-215] et 123,3 [7,8-354] ppm. Les trois insecticides testés ont induit des taux de mortalité inférieurs à 85 % pour la souche Banya II d’A. gambiae s.l. et supérieurs à 98 % pour la souche Bodiman d’A. nili. Les présentes informations devraient être prises en compte pour une meilleure orientation des stratégies de lutte si l’on veut contrôler efficacement les vecteurs dans les localités d’étude.Choosing an appropriate strategy for mosquito control in an eco-climatic facies requires knowledge of vector ecology, including the spatial distribution and productivity of larval habitats and their level of susceptibility to insecticides. This study maps, characterizes the mosquito breeding sites and evaluates the susceptibility to insecticides of malaria vectors to Banya II and Bodiman, two semi-urban and rural areas of the coastal region of Cameroon. The field surveys were conducted in May 2015. The mosquito breeding sites were geo-referenced. For each breeding site, larvae were collected then reared and physico-chemical parameters measured in situ. The susceptibility of vectors to dichlorodiphenyltrichloroethane (DDT), deltamethrin and permethrin was evaluated on the anopheline obtained from larva rearing. A variety of breeding sites has been identified in the study sites (ponds, rivers, ditches, tires, plastic wrap, water storage containers, abandoned containers, papaya holes, bamboo holes). However, Anopheles gambiae s.l, the most abundant species in Banya II was more common in the pools, while Culex poicilipes, the most abundant species in Bodiman was mainly collected in abandoned containers. The two categories of breeding sites had respectively electrical conductivity of 167.5 [16.9-305] and 170.43 [11.6-461] µs/cm, salinity of 90.5 [23.5-157] and 94.63[15-240] g/l and total dissolved solids of 119.6 [20.6-215] and 123.3 [7.8-354] ppm. Insecticides tests revealed mortality rates below 85 % for the Banya II Strain of A. gambiae s.l. and over 98 % for the Bodiman strain of A. nili. These informations should be taken into account for a better orientation of control strategies in order to control effectively the vectors in the study localities

Review of malaria situation in Cameroon: technical viewpoint on challenges and prospects for disease elimination

Abstract Malaria still has a devastating impact on public health and welfare in Cameroon. Despite the increasing number of studies conducted on disease prevalence, transmission patterns or treatment, there are to date, not enough studies summarising findings from previous works in order to identify gaps in knowledge and areas of interest where further evidence is needed to drive malaria elimination efforts. The present study seeks to address these gaps by providing a review of studies conducted so far on malaria in Cameroon since the 1940s to date. Over 250 scientific publications were consulted for this purpose. Although there has been increased scale-up of vector control interventions which significantly reduced the morbidity and mortality to malaria across the country from a prevalence of 41% of the population reporting at least one malaria case episode in 2000 to a prevalence of 24% in 2017, the situation is not yet under control. There is a high variability in disease endemicity between epidemiological settings with prevalence of Plasmodium parasitaemia varying from 7 to 85% in children aged 6 months to 15 years after long-lasting insecticidal nets (LLINs) scale-up. Four species of Plasmodium have been recorded across the country including Plasmodium falciparum, P. malariae, P. ovale and P. vivax. Several primate-infecting Plasmodium spp. are also circulating in Cameroon. A decline of artemisinin-based combinations therapeutic efficacy from 97% in 2006 to 90% in 2016 have been reported. Several mutations in the P. falciparum chloroquine resistance (Pfcrt) and P. falciparum multidrug resistance 1 (Pfmdr1) genes conferring resistance to either 4-amino-quinoleine, mefloquine, halofanthrine and quinine have been documented. Mutations in the Pfdhfr and Pfdhps genes involved in sulfadoxine-pyrimethamine are also on the rise. No mutation associated with artemisinin resistance has been recorded. Sixteen anopheline species contribute to malaria parasite transmission with six recognized as major vectors: An. gambiae, An. coluzzii, An. arabiensis, An. funestus, An. nili and An. moucheti. Studies conducted so far, indicated rapid expansion of DDT, pyrethroid and carbamate resistance in An. gambiae, An. coluzzii, An. arabiensis and An. funestus threatening the performance of LLINs. This review highlights the complex situation of malaria in Cameroon and the need to urgently implement and reinforce integrated control strategies in different epidemiological settings, as part of the substantial efforts to consolidate gains and advance towards malaria elimination in the country

Resting Behaviour of Deltamethrin-Resistant Malaria Vectors, Anopheles arabiensis and Anopheles coluzzii, from North Cameroon: Upshots from a Two-Level Ordinary Logit Model

The current study was conducted in Garoua, Pitoa, and Mayo-Oulo health districts of north Cameroon, in order to investigate the resting behaviour of deltamethrin-resistant Anopheles (An.) gambiae s.l. populations and build a model of their response to the use of Permanet 2.0 long-lasting insecticidal nets (LLINs). Adult mosquitoes were collected in October and November 2011, using spray catches and window exit traps in 29 clusters with LLINs in use. Sampled An. gambiae s.l. were identified down to species and analysed for blood-meal origin, physiological and circumsporozoite protein status. Deltamethrin resistance was assessed using World Health Organization’s (WHO’s) standard protocol. A two-level ordinary logit model was used to relate the resting behaviour and deltamethrin resistance. Identified species of the An. gambiae complex included An. arabiensis (90.6%), An. coluzzii (7.1%) and An. gambiae s.s. (2.3%). They displayed 1.1–4.8% infection rates, 80% indoor-resting density and 56–80% human blood index. Eleven An. gambiae s.l. populations over the 15 tested were resistant to deltamethrin (51–89.5% mortality rates). Model results showed a significant dependence of indoor vector density on increasing deltamethrin resistance (p-value of <0.01). These behavioural and resistance patterns may lead to increasing malaria transmission in study health districts

Implication of Anopheles funestus in malaria transmission in the city of Yaoundé, Cameroon

The contribution of Anopheles funestus to malaria transmission in the urban environment is still not well documented. The present study assesses the implication of An. funestus in malaria transmission in two districts, Nsam and Mendong, in the city of Yaoundé. Adult mosquitoes were collected using Centers for Disease Control and Prevention miniature light traps (CDC-LT) and human landing catches from April 2017 to March 2018 and were identified morphologically to the species level. Those belonging to the Anopheles gambiae complex and to the Anopheles funestus group were further processed by PCR to identify members of each complex/group. Anopheline mosquitoes were analysed to determine their infection status using an enzyme-linked immunosorbent assay. Bioassays were conducted with 2–5-day-old female Anopheles funestus and An. gambiae s.l. to determine their susceptibility to permethrin, deltamethrin and dichlorodiphenyltrichloroethane (DDT). Six anopheline species were collected in the peri-urban district of Mendong: Anopheles gambiae, An. coluzzii, An. funestus, An. leesoni, An. ziemanni and An. marshallii; only four out of the six were recorded in Nsam. Of the two members of the Anopheles gambiae complex collected, An. coluzzii was the most prevalent. Anopheles coluzzii was the most abundant species in Nsam, while An. funestus was the most abundant in Mendong. Both Anopheles funestus and An. gambiae s.l. were found to be infected with human Plasmodium at both sites, and both were found to be resistant to DDT, permethrin, and deltamethrin. This study confirms the participation of An. funestus in malaria transmission in Yaoundé and highlights the need to also target this species for sustainable control of malaria transmission