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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. 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). 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. 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.

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.

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.

Background Malaria, a major global health concern, continues to cause substantial morbidity and mortality, particularly in tropical regions. Traditional malaria diagnostic methods such as microscopy and quantitative polymerase chain reaction (qPCR) are effective but face challenges in field settings because of their requirement for laboratories with specialized equipment and trained personnel. This study presents the development and validation of a portable, cost-effective, field-deployable real-time qPCR platform for detecting Plasmodium species. Methods Field-compatible DNA isolation was performed using DNAzol, and TaqMan probes targeting 18S ribosomal RNA (rRNA) were employed to detect five Plasmodium species— P. falciparum , P. vivax , P. malariae , P. ovale , and P. knowlesi —using the bCUBE qPCR platform. In vitro-cultured P. falciparum and experimentally infected Anopheles gambiae were used to quantify P. falciparum infections, with infection prevalence compared to microscopy. The bCUBE qPCR system was also evaluated under field conditions to detect P. falciparum infections in field-collected An. gambiae mosquitoes. Results The bCUBE qPCR demonstrated a strong linear correlation ( R 2  = 0.993) with a standard laboratory qPCR machine for detecting  P. falciparum  infections. It successfully detected as few as 0.5 parasites/µl of blood, one oocyst in mosquito guts, and 5–10 sporozoites in salivary glands. It was also capable of discriminating between P. falciparum , P. vivax, P. malariae , P. ovale , and P. knowlesi. Field evaluations in Cameroon confirmed its accuracy in identifying  P. falciparum  in mosquito samples, with same-day results. The capability of the bCUBE qPCR system to detect infections in both individual and pooled mosquito surveillance further highlights its potential for in-field large-scale malaria monitoring surveillance. Conclusions The bCUBE qPCR system offers a portable, sensitive, and scalable solution for malaria diagnostics, enabling real-time surveillance in resource-limited settings. Its ability to provide rapid, on-site results reduces the need for centralized laboratory testing, facilitating timely decision-making in malaria control programs. Graphical Abstract

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. 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. 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.

The first dengue outbreak in Sao Tome and Principe was reported in 2022. Entomological investigations were undertaken to establish the typology of Aedes larval habitats, the distribution of Ae. aegypti and Ae. albopictus, the related entomological risk and the susceptibility profile of Ae. aegypti to insecticides, to provide evidence to inform the outbreak response. Entomological surveys were performed in all seven health districts of Sao Tome and Principe during the dry and rainy seasons in 2022. WHO tube and synergist assays using piperonyl butoxide (PBO) and diethyl maleate (DEM) were carried out, together with genotyping of F1534C/V1016I/V410L mutations in Ae. aegypti. Aedes aegypti and Ae. albopictus were found in all seven health districts of the country with high abundance of Ae. aegypti in the most urbanised district, Agua Grande. Both Aedes species bred mainly in used tyres, discarded tanks and water storage containers. In both survey periods, the Breteau (BI > 50), house (HI > 35%) and container (CI > 20%) indices were higher than the thresholds established by WHO to indicate high potential risk of dengue transmission. The Ae. aegypti sampled were susceptible to all insecticides tested except dichlorodiphenyltrichloroethane (DDT) (9.2% mortality, resistant), bendiocarb (61.4% mortality, resistant) and alpha-cypermethrin (97% mortality, probable resistant). A full recovery was observed in Ae. aegypti resistant to bendiocarb after pre-exposure to synergist PBO. Only one Ae. aegypti specimen was found carrying F1534C mutation. These findings revealed a high potential risk for dengue transmission throughout the year, with the bulk of larval breeding occurring in used tyres, water storage and discarded containers. Most of the insecticides tested remain effective to control Aedes vectors in Sao Tome, except DDT and bendiocarb. These data underline the importance of raising community awareness and implementing routine dengue vector control strategies to prevent further outbreaks in Sao Tome and Principe, and elsewhere in the subregion.

Background Urbanization can influence disease vectors by altering larval habitat, microclimates, and host abundance. The global increase in urbanization, especially in Africa, is likely to alter vector abundance and pathogen transmission. We investigated the effect of urbanization and weather on the abundance of two mosquitoes, Aedes aegypti and Aedes albopictus , and infection with dengue, chikungunya, and Zika viruses at 63 sites in six cities spanning a 900-km latitudinal range in Cameroon, Central Africa. Methods We used human landing catches and backpack-mounted aspirators to sample mosquitoes and collected larval habitat, host availability, and weather (temperature, precipitation, humidity) data for each site in each city. We analyzed land use and land cover information and satellite photos at varying radii around sites (100 m to 2 km) to quantify the extent of urbanization and the number of structures around each site. We used a continuous urbanization index (UI; range 0–100) that increased with impermeable surface and decreased with forest cover. Results Urbanization increased larval habitat, human host availability, and Ae. aegypti mosquito abundance. Aedes aegypti abundance increased 1.7% (95% CI 0.69–2.7%) with each 1 unit increase in the urbanization index in all six cities (Douala, Kribi, Yaounde, Ngaoundere, Garoua, and Maroua) with a 5.4-fold increase from UI = 0 to UI = 100, and also increased with rainfall. In contrast, Ae. albopictus abundance increased with urbanization in one city, but showed no influence of urbanization in two other cites. Across three cities, Ae. albopictus abundance increased with rainfall, temperature, and humidity. Finally, we did not detect Zika, dengue, or chikungunya viruses in any specimens, and found weak evidence of interspecific competition in analyses of adult population growth rates. Conclusions These results show that urbanization consistently increases Ae. aegypti abundance across a broad range of habitats in Central Africa, while effects on Ae. albopictus were more variable and the abundance of both species were influenced by rainfall. Future urbanization of Africa will likely increase Ae. aegypti abundance, and climate change will likely alter abundance of both species through changes in precipitation and temperature. Graphical Abstract

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.

Background The number of reports of arboviral outbreaks is increasing and, consequently, the need for effective surveillance and vector control plans for Aedes -borne diseases is becoming more urgent. To explore the current state of knowledge of Aedes arbovirus vectors in Africa, we reviewed studies published between 1980 and 2023 that involved Aedes vector surveillance, vector control or insecticide resistance, with the aim to synthesize information and identify knowledge gaps to guide future Aedes research and control in Africa. Methods Studies conducted in Africa and published between 1980 and 2023 were retrieved from twelve electronic databases using search strings designed to capture relevant concepts. Articles that did not meet the eligibility criteria were excluded during relevance screening. Results Out of 17,337 publications identified, 877 full-text articles were reviewed, of which seven included information on vector surveillance, 56 on vector control and 57 on insecticide resistance. Publications reporting longitudinal data from sustained Aedes vector surveillance systems were only available for Senegal and La Réunion. Aedes vector control studies were principally controlled bioassays or small-scale studies conducted before and after entomological studies which lacked epidemiological outcomes. The most studied methods were larval control ( n  = 21 publications), integrated control combining different interventions ( n  = 7), topical repellents ( n  = 6), environmental management ( n  = 5) and spatial repellents ( n  = 3). Four publications described typical vector control responses during arbovirus epidemics in Africa: these often combined larviciding, ultra-low volume (ULV) space spraying and community engagement to reduce larval sites, alongside active source reduction. There was a lack of high-quality evidence generated through rigorous study design on the effectiveness of control measures in reducing arbovirus transmission in the African context. As a consequence, the scientific basis for evidence-informed decisions in Africa, both for routine Aedes vector control or for outbreak response, remains weak. Insecticide resistance studies focused on adulticides using WHO tube tests ( n  = 43 publications), with larval bioassays relatively less common ( n  = 13). Aedes aegypti ( n  = 53) and Aedes albopictus ( n  = 12) were the only Aedes species tested. The most commonly tested adulticides were permethrin and deltamethrin (pyrethroids); bendiocarb (carbamate); and dichlorodiphenyltrichloroethane (DDT; organochlorine), although the results were rarely reported in connection with decision-making about Aedes control. Results of the most relevant adulticides indicated that Ae. aegypti populations were generally susceptible to malathion (organophosphate), but resistance to permethrin and deltamethrin was detected in West and Central Africa. Most studies pre-dated the revised WHO guidance, and insecticide concentrations were mostly those recommended for Anopheles susceptibility testing that use relatively higher discriminating doses, and thus likely underestimate true Aedes resistance levels. Larval susceptibility bioassays were conducted with temephos ( n  = 12) and Bacillus thuringiensis israelensis ( n  = 6). Temephos resistance was only detected in Cabo Verde following several decades of use. Conclusions Given the increasing frequency of arbovirus epidemics in Africa, countries urgently need to develop plans for emergency response and robust control strategies that make use of evidence from good-quality studies to strengthen resilience.

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 χ 2 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.