Spatial distribution and insecticide resistance profile of Aedes aegypti and Aedes albopictus in Douala, the most important city of Cameroon.

Prevention and control of Aedes-borne viral diseases such as dengue rely on vector control, including the use of insecticides and reduction of larval sources. However, this is threatened by the emergence of insecticide resistance. This study aimed to update the spatial distribution, the insecticide resistance profile of A. aegypti and A. albopictus and the potential resistant mechanisms implicated in the city of Douala. Immature stages of Aedes were collected in August 2020 in eight neighbourhoods in Douala and reared to adult stages. Adult bioassays, and piperonyl butoxide (PBO) synergist assays were carried out according to World Health Organization recommendations. Expression of some candidate metabolic genes including Cyp9M6F88/87, Cyp9J28a, Cyp9J10 and Cyp9J32 in A. aegypti, and Cyp6P12 in A. albopictus were assessed using qPCR. A. aegypti adults G0 were screened using real time melting curve qPCR analyses to genotype the F1534C, V1016I and V410L Aedes kdr mutations. Overall, A. aegypti is the predominant Aedes species, but analyses revealed that both A. albopictus and A. aegypti coexist in all the prospected neighbourhoods of Douala. High level of resistance was observed to three pyrethroids tested in both Aedes species. In A. aegypti a lower mortality rate was reported to permethrin (5.83%) and a higher mortality rate to deltamethrin (63.74%). Meanwhile, for A. albopictus, lower (6.72%) and higher (84.11%) mortality rates were reported to deltamethrin. Similar analysis with bendiocarb, revealed for A. aegypti a loss of susceptibility. However, in A. albopictus samples, analyses revealed a susceptibility in Logbessou, and confirmed resistance in Kotto (59.78%). A partial recovery of mortality was found to insecticides after pre-exposure to PBO. Cyp6P12 was found significantly overexpressed in A. albopictus permethrin resistant and Cyp9M6F88/87 for A. aegypti deltamethrin resistant. F1534C, V1016I and V410L mutations were detected in A. aegypti from different neighbourhoods and by considering the combination of these three kdr 14 genotypes were found. These findings provide relevant information which should be capitalised in the implementation of arbovirus vector control strategies and insecticide resistance management.

Spatial distribution of insecticide resistant populations of Aedes aegypti and Ae. albopictus and first detection of V410L mutation in Ae. aegypti from Cameroon.

BACKGROUND: Dengue (DENV), chikungunya (CHIKV) and Zika virus (ZIKV), are mosquito-borne viruses of medical importance in most tropical and subtropical regions. Vector control, primarily through insecticides, remains the primary method to prevent their transmission. Here, we evaluated insecticide resistance profiles and identified important underlying resistance mechanisms in populations of Aedes aegypti and Ae. albopictus from six different regions in Cameroon to pesticides commonly used during military and civilian public health vector control operations. METHODS: Aedes mosquitoes were sampled as larvae or pupae between August 2020 and July 2021 in six locations across Cameroon and reared until the next generation, G1. Ae. aegypti and Ae. albopictus adults from G1 were tested following World Health Organization (WHO) recommendations and Ae. aegypti G0 adults screened with real time melting curve qPCR analyses to genotype the F1534C, V1016I and V410L Aedes kdr mutations. Piperonyl butoxide (PBO) assays and real time qPCR were carried out from some cytochrome p450 genes known to be involved in metabolic resistance. Statistical analyses were performed using Chi-square test and generalized linear models. RESULTS: Loss of susceptibility was observed to all insecticides tested. Mortality rates from tests with 0.25% permethrin varied from 24.27 to 85.89% in Ae. aegypti and from 17.35% to 68.08% in Ae. albopictus. Mortality rates for 0.03% deltamethrin were between 23.30% and 88.20% in Ae. aegypti and between 69.47 and 84.11% in Ae. albopictus. We found a moderate level of resistance against bendiocarb, with mortality rates ranging from 69.31% to 90.26% in Ae. aegypti and from 86.75 to 98.95% in Ae. albopictus. With PBO pre-exposure, we found partial or fully restored susceptibility to pyrethroids and bendiocarb. The genes Cyp9M6F88/87 and Cyp9J10 were overexpressed in Ae. aegypti populations from Douala sites resistant to permethrin and deltamethrin. Cyp6P12 was highly expressed in alphacypermethrin and permethrin resistant Ae. albopictus samples. F1534C and V1016I mutations were detected in A. aegypti mosquitoes and for the first time V410L was reported in Cameroon. CONCLUSIONS: This study revealed that Ae. aegypti and Ae. albopictus are resistant to multiple insecticide classes with multiple resistance mechanisms implicated. These findings could guide insecticide use to control arbovirus vectors in Cameroon.

First detection of F1534C knockdown resistance mutation in Aedes aegypti (Diptera: Culicidae) from Cameroon.

BACKGROUND: Aedes borne viral diseases, notably dengue, are increasingly reported in Cameroon with Aedes aegypti being a major vector. Data on insecticide resistance of this vector and underlying mechanisms needed for outbreak preparedness remain scarce in Cameroon. Here, we present the nationwide distribution of insecticide resistance in Ae. aegypti and investigate the potential resistance mechanisms involved. METHODS: Immature stages of Ae. aegypti were collected between March and July 2017 in 13 locations across Cameroon and reared until G1/G2/G3 generation. Larval, adult bioassays, and piperonyl butoxide (PBO) synergist assays were carried out according to World Health Organization guidelines. F1534C mutation was genotyped using allele specific polymerase chain reaction in field collected adults (Go) and the polymorphism of the sodium channel gene was assessed. The χ2 test was used to compare the mortality rate between bioassays with insecticides only and bioassays after preexposure to PBO synergist. RESULTS: Larval bioassay revealed that all the three populations tested with temephos were susceptible. Adult bioassays showed a good level of susceptibility toward both pyrethroids tested, 0.25% permethrin and 0.05% deltamethrin, with six out of 10 populations susceptible. However, two populations (Douala and Edéa) were resistant (deltamethrin [73.2-92.5% mortality], permethrin [2.6-76.3% mortality]). The resistance to 4% dichlorodiphenyltrichloroethane was observed in four out of 10 populations tested (16.8-87.1% mortality). Resistance was also reported to carbamates including 0.1% propoxur (60.8-87.1% mortality) and to 0.1% bendiocarb (82.9% mortality). All populations tested were fully susceptible to 1% fenitrothion. A partial recovery of susceptibility was observed in the pyrethroid resistant population of Douala after pre-exposed to PBO suggesting the implication of cytochrome P450 monoxygenases permethrin resistance. Genotyping and sequencing detected the F1534C kdr mutation in the two pyrethroid resistant locations of Edéa and Douala, with allelic frequency of 3.3% and 33.3% respectively. However, the high genetic diversity of the sodium channel gene supports the recent introduction of this mutation in Cameroon. CONCLUSIONS: This study revealed the contrasting resistance profiles to insecticides of Ae. aegypti populations in Cameroon suggesting that, instead of a unique nationwide control approach, a regionally adapted strategy will be needed to control this vector. The localised distribution of the F1534C kdr mutation supports this region-specific control strategy.

Patterns of Ecological Adaptation of Aedes aegypti and Aedes albopictus and Stegomyia Indices Highlight the Potential Risk of Arbovirus Transmission in Yaoundé, the Capital City of Cameroon.

The dynamic of arbovirus vectors such as Aedes aegypti and Ae. albopictus remains poorly understood in large cities in central Africa. Here, we compared the larval ecology, geographical distribution and degree of infestation of Ae. aegypti and Ae. albopictus in Yaoundé, the capital city of Cameroon, and estimated their Stegomyia indices revealing a significant potential risk of arbovirus transmission. An entomological survey was conducted in April-May 2018 in a cluster of houses randomly selected. Each selected house was inspected, the number of inhabitants was recorded, and potential and positive containers for Aedes were characterized. Stegomyia and pupae-based indices were estimated. Overall, 447 houses and 954 containers were inspected comprising 10,801 immature stages of Aedes with 84.95% of Ae. albopictus and 15.05% of Ae. aegypti. Both species bred mainly in discarded tanks and used tyres, associated with turbid water and the presence of plant debris inside containers. Aedes albopictus was the most prevalent species in almost all neighbourhoods. The house index, Breteau index, and container index were higher for Ae. albopictus (38.26%, 71.81%, and 29.61%) compared to those of Ae. aegypti (25.73%, 40.93%, and 16.88%). These indices are high compared to the thresholds established by Pan American Health Organization and World Health Organization, which suggests a high potential risk of arbovirus transmission.

Nationwide profiling of insecticide resistance in Aedes albopictus (Diptera: Culicidae) in Cameroon.

The Asian mosquito, Aedes albopictus (Skuse), is an invasive mosquito which has become one of the most important vectors of dengue, Zika, and chikungunya viruses worldwide. This species was reported for the first time in Cameroon in early 2000s and became the dominant Aedes species in the urban areas in the southern part of Cameroon but remain poorly characterized. Here, we assessed the susceptibility profile of A. albopictus collected throughout Cameroon and investigated the potential resistance mechanisms involved. Immature stages of A. albopictus were collected between March and July 2017 in 15 locations across Cameroon and reared until G1/G2 generation. Larval, adult bioassays, and synergists [piperonyl butoxide (PBO) and diethyl maleate (DEM)] assays were carried out according to WHO recommendations. F1534C mutation was genotyped in field collected adults (Go) using allele specific PCR. All tested populations were susceptible to both larvicides, temephos and Bacillus thuringiensis israelensis (Bti), after larval bioassays. Adult bioassays revealed a high level of resistance of A. albopictus to 4% DDT with mortality rates ranging from 12.42% in Bafang to 75.04% in Kumba. The resistance was reported also in 0.05% deltamethrin, 0.25% permethrin, and 0.1% propoxur in some locations. A loss of susceptibility to 0.1% bendiocarb was found in one of three populations analysed. A full susceptibility to 1% fenitrothion were observed across the country. A full recovery or partial of susceptibility was observed in A. albopictus when pre-exposed to PBO or DEM and then to DDT and permethrin, respectively. The F1534C kdr mutation was not detected in A. albopictus. This study showed that the susceptibility profile of A. albopictus to insecticide vary according to the sampling location and insecticides used. These findings are useful to planning vector control program against arbovirus vectors in Cameroon and can be used as baseline data for further researches.

Different populations of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) from Central Africa are susceptible to Zika virus infection.

Zika virus (ZIKV) is a Flavivirus (Flaviviridae) transmitted to humans mainly by the bite of an infected Aedes mosquitoes. Aedes aegypti is the primary epidemic vector of ZIKV and Ae. albopictus, the secondary one. However, the epidemiological role of both Aedes species in Central Africa where Ae. albopictus was recently introduced is poorly characterized. Field-collected strains of Ae. aegypti and Ae. albopictus from different ecological settings in Central Africa were experimentally infected with a ZIKV strain isolated in West Africa. Mosquitoes were analysed at 14- and 21-days post-exposure. Both Ae. aegypti and Ae. albopictus were able to transmit ZIKV but with higher overall transmission efficiency for Ae. aegypti (57.9%) compared to Ae. albopictus (41.5%). In addition, disseminated infection and transmission rates for both Ae. aegypti and Ae. albopictus varied significantly according to the location where they were sampled from. We conclude that both Ae. aegypti and Ae. albopictus are able to transmit ZIKV and may intervene as active Zika vectors in Central Africa. These findings could contribute to a better understanding of the epidemiological transmission of ZIKV in Central Africa and develop suitable strategy to prevent major ZIKV outbreaks in this region.

Contrasting resistance patterns to type I and II pyrethroids in two major arbovirus vectors Aedes aegypti and Aedes albopictus in the Republic of the Congo, Central Africa.

BACKGROUND: In the Republic of Congo, with two massive outbreaks of chikungunya observed this decade, little is known about the insecticide resistance profile of the two major arbovirus vectors Aedes aegypti and Aedes albopictus. Here, we established the resistance profile of both species to insecticides and explored the resistance mechanisms to help Congo to better prepare for future outbreaks. METHODS: Immature stages of Ae. aegypti and Ae. albopictus were sampled in May 2017 in eight cities of the Republic of the Congo and reared to adult stage. Larval and adult bioassays, and synergist (piperonyl butoxide [PBO]) assays were carried out according to WHO guidelines. F1534C mutation was genotyped in field collected adults in both species and the polymorphism of the sodium channel gene assessed in Ae. aegypti. RESULTS: All tested populations were susceptible to temephos after larval bioassays. A high resistance level was observed to 4% DDT in both species countrywide (21.9-88.3% mortality). All but one population (Ae. aegypti from Ngo) exhibited resistance to type I pyrethroid, permethrin, but showed a full susceptibility to type II pyrethroid (deltamethrin) in almost all locations. Resistance was also reported to 1% propoxur in Ae. aegypti likewise in two Ae. albopictus populations (Owando and Ouesso), and the remaining were fully susceptible. All populations of both species were fully susceptible to 1% fenitrothion. A full recovery of susceptibility was observed in Ae. aegypti and Ae. albopictus when pre-exposed to PBO and then to propoxur and permethrin respectively. The F1534C kdr mutation was not detected in either species. The high genetic variability of the portion of sodium channel spanning the F1534C in Ae. aegypti further supported that knockdown resistance probably play no role in the permethrin resistance. CONCLUSIONS: Our study showed that both Aedes species were susceptible to organophosphates (temephos and fenitrothion), while for other insecticide classes tested the profile of resistance vary according to the population origin. These findings could help to implement better and efficient strategies to control these species in the Congo in the advent of future arbovirus outbreaks.

Risk of dengue in Central Africa: Vector competence studies with Aedes aegypti and Aedes albopictus (Diptera: Culicidae) populations and dengue 2 virus.

INTRODUCTION: Dengue is the most important mosquito-borne diseases worldwide but was considered scarce in West-Central Africa. During the last decade, dengue outbreaks have increasingly been reported in urban foci in this region suggesting major epidemiological changes. However, in Central Africa where both vectors, Aedes aegypti and Aedes albopictus are well established, the role of each species in dengue transmission remains poorly investigated. METHODOLOGY/PRINCIPAL FINDINGS: Field-collected strains of Ae. aegypti and Ae. albopictus from different ecological settings in Central Africa were experimentally challenged with dengue 2 virus (DENV-2). Mosquitoes were analysed at 14- and 21-days post-infection. Analysis provide evidence that both Ae. aegypti and Ae. albopictus in Central Africa were able to transmit dengue virus with Ae. aegypti exhibiting a higher transmission rate. Unexpectedly, two Ae. aegypti populations from Bénoué and Maroua, in northern Cameroon, were not able to transmit DENV-2. CONCLUSIONS/SIGNIFICANCE: We conclude that both Ae. aegypti and Ae. albopictus are susceptible to DENV-2 and may intervene as active dengue vectors. These findings highlight the urgent need to plan a vector surveillance program and control methods against dengue vectors in Central Africa in order to prevent future outbreaks.

Potential of Aedes albopictus and Aedes aegypti (Diptera: Culicidae) to transmit yellow fever virus in urban areas in Central Africa.

Yellow Fever (YF) remains a major public health issue in Sub-Saharan Africa and South America, despite the availability of an effective vaccine. In Africa, most YF outbreaks are reported in West Africa. However, urban outbreaks occurred in 2016 in both Angola and the Democratic Republic of Congo (DRC), and imported cases were reported in Chinese workers coming back from Africa. In Central Africa, Cameroon and the Republic of Congo host a high proportion of non-vaccinated populations increasing the risk of urban outbreaks. The main vector is Aedes aegypti and possibly, Aedes albopictus, both being anthropophilic and domestic mosquitoes. Here, we provide evidence that both Ae. aegypti and Ae. albopictus in Cameroon and the Republic of Congo are able to transmit Yellow fever virus (YFV) with higher rates of infection, dissemination, and transmission for Ae. aegypti. We conclude that the potential of both Aedes species to transmit YFV could increase the risk of urban YF transmission and urge public health authorities to intensify their efforts to control domestic vectors, and extend vaccine coverage to prevent major YFV outbreak.

Update on the geographical distribution and prevalence of Aedes aegypti and Aedes albopictus (Diptera: Culicidae), two major arbovirus vectors in Cameroon.

INTRODUCTION: Arboviral diseases including dengue are increasingly spreading in the tropical/subtropical world including Africa. Updated knowledge on the distribution and abundance of the major vectors Aedes aegypti and Aedes albopictus constitutes crucial surveillance action to prepare African countries such as Cameroon for potential arbovirus outbreaks. Here, we present a nationwide survey in Cameroon to assess the current geographical distribution and prevalence of both vectors including a genetic diversity profiling of Ae. albopictus (invasive species) using mitochondrial DNA. METHODS: Immature stages of Aedes were collected between March and August 2017 in 29 localities across Cameroon following north-south and east-west transects. Larvae and pupae were collected from several containers in each location, reared to adult and morphologically identified. Genetic diversity of Ae. albopictus from 16 locations were analysed using Cytochrome Oxidase I gene (COI). RESULTS: In total, 30,381 immature stages of Aedes with an average of 646.40±414.21 per location were identified across the country comprising 69.3% of Ae. albopictus and 30.7% of Ae. aegypti. Analysis revealed that Ae. aegypti is still distributed nation widely whereas Ae. albopictus is limited to the southern part, around 6°4'N. However, Ae. albopictus is the most prevalent species in all southern locations where both species are sympatric except in Douala where Ae. aegypti is predominant. This suggests that factors such as climate, vegetation, and building density impact the distribution of both species in Cameroon. Mitochondrial DNA analysis revealed a low genetic diversity in Ae. albopictus populations with a major common haplotype resulting in low haplotype diversity ranging from 0.13 to 0.65 and 0.35 for the total sample. Similarly, low nucleotide diversity was also reported varying from 0.0000 to 0.0017 with an overall index of 0.0008. This low genetic polymorphism is consistent with the recent introduction of Ae. albopictus in Cameroon. CONCLUSION: This updated distribution of arbovirus vectors across Cameroon will help in planning vector control programme against possible outbreak of arbovirus related diseases in the country.

Temporal distribution and insecticide resistance profile of two major arbovirus vectors Aedes aegypti and Aedes albopictus in Yaoundé, the capital city of Cameroon.

BACKGROUND: Aedes aegypti and Ae. albopictus are the major epidemic vectors of several arbovirus diseases such as yellow fever, dengue, Zika and chikungunya worldwide. Both Aedes vectors are presents in Cameroon; however, knowledge on the dynamic of the distribution of these species across cities and their resistance profile to insecticide are limited. Here, we assessed the current distribution of Ae. aegypti and Ae. albopictus in Yaoundé, the Capital City, established the resistance profile to insecticides and explored the resistance mechanisms involved. METHODS: Immature stages of Aedes were sampled in several breeding sites in December 2015 (dry season) and June 2016 (rainy season) in three central neighborhoods and four peripheral neighborhoods and reared to adult stage. The G0 adults were used for molecular identification and genotyping of F1534C mutation in Ae. aegypti. Bioassays and piperonyl butoxide (PBO) assays were carried out according to WHO guidelines. RESULTS: Analysis revealed that both species Ae. aegypti and Ae. albopictus are present in all prospected sites in Yaounde. However, in the dry season Ae. aegypti is most abundant in neighborhoods located in downtown. In contrast, Ae. albopictus was found most prevalent in suburbs whatever the season and in downtown during the rainy season. Bioassay analysis showed that both Ae. aegypti and Ae. albopictus, are resistant to 0.05% deltamethrin, 0.1% bendiocarb and 4% dichlorodiphenyltrichloroethane (DDT). A decreased of susceptibility to 0.75% permethrin and a full susceptibility to malathion 5% was observed. The mortality rate was increased after pre-exposure to synergist PBO. None of Ae. aegypti assayed revealed the presence of F1534C mutation. CONCLUSION: These findings are useful to planning vector control programme against arbovirus vectors in Cameroon and can be used as baseline in Africa where data on Aedes resistance is very scarce to plan further works.