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

Knowledge, attitudes, and practices regarding malaria control among communities living in the south Cameroon forest region.

This study assessed knowledge, attitudes, and practices (KAP) regarding malaria among communities living in the equatorial forest region of south Cameroon. The study was conducted in Olama and Nyabessan. Interviews were undertaken using a semi-structured questionnaire for data collection on KAP, while malaria rapid diagnostic testing, using SD BIOLINE kits, was employed for malaria parasite detection. In total, 186 heads of households (HoH), comprising 105 (56.45%) males and 81 (43.45%) females, were interviewed. The majority of HoH demonstrated good knowledge of malaria (86.56%;  = 161) and control measures, with a high proportion of long-lasting insecticidal net (LLIN) ownership (96.8%;  = 180). More than two-thirds (81.1%;  = 151) of households owned at least one LLIN for two people. The majority of HoH (85.40%) declared visiting hospitals or clinics in cases of suspected malaria. Malaria parasite prevalence was high in the two study sites (63.9% in Nyabessan and 48.65% in Olama), and varied according to age, house type, and sleeping time. The study indicated that despite good knowledge of malaria, high possession and utilization of control measures by population, transmission of malaria still persist in the area. The study stress the need for implementing additional control measures to improve the fight against malaria in the area

Habitat and Seasonality Affect Mosquito Community Composition in the West Region of Cameroon.

To identify potential sylvatic, urban and bridge-vectors that can be involved in current or future virus spillover from wild to more urbanised areas, entomological field surveys were conducted in rural, peri-urban and urban areas spanning the rainy and dry seasons in western Cameroon. A total of 2650 mosquitoes belonging to 37 species and eight genera were collected. Mosquito species richness was significantly influenced by the specific combination of the habitat type and the season. The highest species richness was found in the peri-urban area (S = 30, Chao1 = 121 ± 50.63, ACE = 51.97 ± 3.88) during the dry season (S = 28, Chao1 = 64 ± 25.7, ACE = 38.33 ± 3.1). Aedes (Ae.) africanus and Culex (Cx.) moucheti were only found in the rural and peri-urban areas, while Cx. pipiens s.l. and Ae. aegypti were only found in the urban area. Cx. (Culiciomyia) spp., Cx. duttoni and Ae. albopictus were caught in the three habitat types. Importantly, approximately 52% of the mosquito species collected in this study have been implicated in the transmission of diverse arboviruses. This entomological survey provides a catalogue of the different mosquito species that may be involved in the transmission of arboviruses. Further investigations are needed to study the vectorial capacity of each mosquito species in arbovirus transmission

Status of Insecticide Resistance and Its Mechanisms in and Populations from Forest Settings in South Cameroon.

A key factor affecting malaria vector control efforts in Cameroon is the rapid expansion of insecticide resistance in s.l ) populations; however, mechanisms involved in insecticide resistance in forest mosquito populations are still not well documented yet. The present study was conducted to screen molecular mechanisms conferring insecticide resistance in s.l. populations from the South Cameroon forest region. WHO bioassays were conducted with F0 females aged three to four days from forest (Sangmelima, Nyabessan, and Mbandjock) and urban sites (Yaoundé (Bastos and Nkolondom)), against pyrethroids (permethrin 0.75% and deltamethrin 0.05%) and carbamates (bendiocarb 0.1%). Members of the s.l. species complex were identified using molecular diagnostic tools. TaqMan assays were used to screen for target site mutations. The expression profiles of eight genes implicated in insecticide resistance were assessed using RT-qPCR. Cuticle hydrocarbon lipids were measured to assess their potential implication in insecticide resistance. Both and were detected. was highly prevalent in Sangmelima, Nyabessan, Mbandjock, and Nkolondom. was the only species found in the Yaoundé city center (Bastos). Low mortality rate to both pyrethroids and bendiocarb was recorded in all sites. High frequency of L1014F allele (75.32-95.82%) and low frequencies of L1014S (1.71-23.05%) and N1575Y (5.28-12.87%) were recorded. The G119S mutation (14.22-35.5%) was detected for the first time in populations from Cameroon. This mutation was rather absent from populations. The detoxification genes , , , , as well as which catalyzes epicuticular hydrocarbon biosynthesis, were found to be overexpressed in at least one population. The total cuticular hydrocarvbon content, a proxy of cuticular resistance, did not show a pattern associated with pyrethroid resistance in these populations. The rapid emergence of multiple resistance mechanisms in s.l. population from the South Cameroon forest region is of big concern and could deeply affect the sustainability of insecticide-based interventions strategies in this region

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

Bionomics of Anopheline species and malaria transmission dynamics along an altitudinal transect in Western Cameroon

<p>Abstract</p> <p>Background</p> <p>Highland areas of Africa are mostly malaria hypoendemic, due to climate which is not appropriate for anophelines development and their reproductive fitness. In view of designing a malaria control strategy in Western Cameroon highlands, baseline data on anopheline species bionomics were collected.</p> <p>Methods</p> <p>Longitudinal entomological surveys were conducted in three localities at different altitudinal levels. Mosquitoes were captured when landing on human volunteers and by pyrethrum spray catches. Sampled <it>Anopheles </it>were tested for the presence of <it>Plasmodium </it>circumsporozoite proteins and their blood meal origin with ELISA. Entomological parameters of malaria epidemiology were assessed using Mac Donald's formula.</p> <p>Results</p> <p>Anopheline species diversity and density decreased globally from lowland to highland. The most aggressive species along the altitudinal transect was <it>Anopheles gambiae </it>s.s. of S molecular form, followed in the lowland and on the plateau by <it>An. funestus</it>, but uphill by <it>An. hancocki</it>. <it>An. gambiae </it>and <it>An. ziemanni </it>exhibited similar seasonal biting patterns at the different levels, whereas different features were observed for <it>An. funestus</it>. Only indoor resting species could be captured uphill; it is therefore likely that endophilic behaviour is necessary for anophelines to climb above a certain threshold. Of the ten species collected along the transect, only <it>An. gambiae </it>and <it>An. funestus </it>were responsible for malaria transmission, with entomological inoculation rates (EIR) of 90.5, 62.8 and zero infective bites/human/year in the lowland, on the plateau and uphill respectively. The duration of gonotrophic cycle was consistently one day shorter for <it>An. gambiae </it>as compared to <it>An. funestus </it>at equal altitude. Altitudinal climate variations had no effect on the survivorship and the subsequent life expectancy of the adult stage of these malaria vectors, but most probably on aquatic stages. On the contrary increasing altitude significantly extended the duration of gonotrophic cycle and reduced: the EIR, their preference to human blood and consequently the malaria stability index.</p> <p>Conclusion</p> <p>Malaria epidemiological rooting in the outskirts of Western Cameroon highlands evolves with increasing altitude, gradually from stable to unstable settings. This suggests a potential risk of malaria epidemic in highlands, and the need for a continuous epidemiological surveillance.</p

Increased prevalence of insecticide resistance in Anopheles coluzzii populations in the city of Yaoundé, Cameroon and influence on pyrethroid-only treated bed net efficacy

In Cameroon, pyrethroid-only long-lasting insecticidal nets (LLINs) are still largely used for malaria control. The present study assessed the efficacy of such LLINs against a multiple-resistant population of the major malaria vector, Anopheles coluzzii, in the city of Yaoundé via a cone bioassay and release-recapture experimental hut trial. Susceptibility of field mosquitoes in Yaoundé to pyrethroids, DDT, carbamates and organophosphate insecticides was investigated using World Health Organization (WHO) bioassay tube tests. Mechanisms of insecticide resistance were characterised molecularly. Efficacy of unwashed PermaNet 2.0 was evaluated against untreated control nets using a resistant colonised strain of An. coluzzii. Mortality, exophily and blood feeding inhibition were estimated. Field collected An. coluzzii displayed high resistance with mortality rates of 3.5% for propoxur (0.1%), 4.16% for DDT (4%), 26.9% for permethrin (0.75%), 50.8% for deltamethrin (0.05%), and 80% for bendiocarb (0.1%). High frequency of the 1014F west-Africa kdr allele was recorded in addition to the overexpression of several detoxification genes, such as Cyp6P3, Cyp6M2, Cyp9K1, Cyp6P4 Cyp6Z1 and GSTe2. A low mortality rate (23.2%) and high blood feeding inhibition rate (65%) were observed when resistant An. coluzzii were exposed to unwashed PermaNet 2.0 net compared to control untreated net (p < 0.001). Furthermore, low personal protection (52.4%) was observed with the resistant strain, indicating reduction of efficacy. The study highlights the loss of efficacy of pyrethroid-only nets against mosquitoes exhibiting high insecticide resistance and suggests a switch to new generation bed nets to improve control of malaria vector populations in Yaoundé

Assessment of the impact of the biological larvicide VectoMax G: Combination of Bacillus thuringiensis and Lysinibacillus sphaericus on non-target aquatic organisms in Yaoundé-Cameroon

There has been a renewed interest for larviciding during the recent decade. Although biological larvicides are considered not to be harmful to non-target organisms, there is still not sufficient data on the effect of new long-lasting larvicide formulations such as VectoMax G combining and on the environment especially on non-target organisms. The present study aimed to assess the possible influence of VectoMax G on the diversity and abundance of the aquatic fauna cohabiting with mosquito larvae in breeding habitats during a larviciding trial in the city of Yaoundé. Twelve districts of the city of Yaoundé divided into 6 intervention and 6 control sites were chosen for the study. In each district 4 semi-permanent or permanent aquatic habitats were followed. VectoMax G application was done once every two weeks during 6 months and aquatic organisms were collected 48 h after each treatment. All collected organisms were brought to the laboratory for identification. Physico-chemical parameters were recorded as well. A high diversity of the zooplankton was recorded in the intervention areas with 28 species collected against 14 species in the control areas. Cladocerans were the most represented group in both sites while Ostracods were found only in control sites. A total of 19 macro-invertebrates species were recorded in the control areas vs 16 species in the intervention areas. Gasteropods were the most represented groups of macro-invertebrates. Vertebrates such as larvivorous fishes and amphibians larvae were also found in approximately similar densities in both sites. The study indicated no significant influence of larviciding with VectoMax G on the diversity and abundance of the non-target aquatic fauna in the city of Yaoundé. [Abstract copyright: © 2023 Published by Elsevier Ltd.

Aedes Mosquito Distribution along a Transect from Rural to Urban Settings in Yaoundé, Cameroon

Introduction: The surveillance of mosquito vectors is important for the control of arboviruses diseases worldwide. Detailed information on the bionomics and distribution of their main vectors, Aedes aegypti and Aedes albopictus, is essential for assessing disease transmission risk and for better planning of control interventions. Methods: Entomological surveys were carried out from November 2019 to November 2020 in six localities of Yaoundé city following a transect from urban to rural settings: two urban (Obili, Mvan), two peri-urban (Simbock, Ahala) and two rural areas (Lendom, Elig-essomballa)—during rainy and dry seasons. All water containers were inspected. Aedes mosquito abundance, species distribution and seasonal distribution patterns were compared using generalized linear models. Stegomyia indexes were estimated to determine the risk of arbovirus transmission. Results: A total of 6332 mosquitoes larvae were collected (2342 in urban areas, 1694 in peri-urban areas and 2296 in rural sites). Aedes species recorded included Ae. albopictus, Ae. aegytpi, Ae. simpsoni and Aedes spp. High mosquito abundance was registered in the rainy season (4706) compared to the dry season (1626) (p < 0.0001). Ae. albopictus was the most abundant Aedes species in urban (96.89%) and peri-urban (95.09%) sites whereas Ae. aegypti was more prevalent in rural sites (68.56%) (p < 0.0001). Both species were found together in 71 larval habitats. Ae. albopictus was mostly found in discarded tires (42.51%), whereas Ae. aegypti was more prevalent in plastic containers used for storing water (65.87%). The majority of Aedes mosquitoes’ breeding places were situated close to human dwellings (0–10 m). Conclusion: Uncontrolled urbanization seems to greatly favour the presence of Aedes mosquito species around human dwellings in Yaoundé. Controlling Aedes mosquito distribution is becoming urgent to reduce the risk of arbovirus outbreaks in the city of Yaound

An update on the mosquito fauna and mosquito-borne diseases distribution in Cameroon

The expansion of mosquito-borne diseases such as dengue, yellow fever, and chikungunya in the past 15 years has ignited the need for active surveillance of common and neglected mosquito-borne infectious diseases. The surveillance should be designed to detect diseases and to provide relevant field-based data for developing and implementing effective control measures to prevent outbreaks before significant public health consequences can occur. Mosquitoes are important vectors of human and animal pathogens, and knowledge on their biodiversity and distribution in the Afrotropical region is needed for the development of evidence-based vector control strategies. Following a comprehensive literature search, an inventory of the diversity and distribution of mosquitoes as well as the different mosquito-borne diseases found in Cameroon was made. A total of 290 publications/reports and the mosquito catalogue website were consulted for the review. To date, about 307 species, four subspecies and one putative new species of Culicidae, comprising 60 species and one putative new species of Anopheles, 67 species and two subspecies of Culex, 77 species and one subspecies of Aedes, 31 species and one subspecies of Eretmapodites, two Mansonia, eight Coquillettidia, and 62 species with unknown medical and veterinary importance (Toxorhynchites, Uranotaenia, Mimomyia, Malaya, Hodgesia, Ficalbia, Orthopodomyia, Aedeomyia, and Culiseta and Lutzia) have been collected in Cameroon. Multiple mosquito species implicated in the transmission of pathogens within Anopheles, Culex, Aedes, Eretmapodites, Mansonia, and Coquillettidia have been reported in Cameroon. Furthermore, the presence of 26 human and zoonotic arboviral diseases, one helminthic disease, and two protozoal diseases has been reported. Information on the bionomics, taxonomy, and distribution of mosquito species will be useful for the development of integrated vector management programmes for the surveillance and elimination of mosquito-borne diseases in Cameroon