Background: The rapid and unplanned urbanization of African cities is considered to increase the risk of urban malaria transmission. The present study objective was to assess factors influencing the spatio-temporal distribution of Anopheles gambiae s.l. larvae in the city of Yaoundé, Cameroon. Methods: All water bodies were checked once every 2 months for the presence of mosquito larvae from March 2017 to May 2018 in 32 districts of Yaoundé. Physico-chemical characteristics including the size, depth, turbidity, pH, temperature, conductivity, sulfates, organophosphates, hydrogen peroxide (H₂O₂), conductivity, iron and calcium were recorded and analyzed according to anopheline larvae presence or absence. High resolution satellite images from landsat sentinel Enhanced Thematic Mapper were used for spatial mapping of both field and environmental variables. Bivariate and multivariate logistic regression models were used to identify variables closely associated with anopheline larvae distribution. Results: A total of 18 696 aquatic habitats were checked and only 2942 sites (15.7%) contained anopheline larvae. A high number of sites with anopheline larvae (≥ 69%) presented late instar larvae (L3, L4 and pupae). Anopheline mosquito larvae were sampled from a variety of breeding sites including puddles (51.6%), tire prints (12.9%), wells (11.7%) and drains (11.3%). Bivariate logistic regression analyses associated anopheline larvae presence with the absence of predators, absence of algae, absence of vegetation and depth of less than 1 m. Conductivity, turbidity, organophosphates, H₂O₂ and temperature were significantly high in breeding sites with anopheline larvae than in breeding sites without these larvae (P < 0.1). Anopheline species collected included An. coluzzii (91.1%) and An. gambiae s.s. (8.9%). GIS mapping indicated a heterogeneous distribution of anopheline breeding habitats in the city of Yaoundé. Land cover analysis indicated high variability of the city of Yaoundé’s landscape. Conclusions: The data confirms adaptation of An. gambiae s.l. to the urban domain in the city of Yaoundé and calls for urgent actions to improve malaria vector control.

The spread of pyrethroid resistance in malaria vectors is a major threat affecting the performance of current control measures. However, there is still not enough information on the resistance profile of mosquitoes to carbamates and organophosphates which could be used as alternatives. The present study assessed the resistance profile of Anopheles gambiae s.l. to bendiocarb and malathion, at the phenotypic and molecular levels, in different eco-epidemiological settings in Cameroon. Anopheles gambiae s.l. mosquitoes were collected from four eco-epidemiological settings across the country and their susceptibility level to bendiocarb and malathion was determined using WHO tubes bioassays. The ace-1 target site G119S mutation was screened by PCR. Reverse Transcription quantitative PCR 3-plex TaqMan assays were used to quantify the level of expression of eight genes associated with metabolic resistance. Resistance to malathion and/or bendiocarb was recorded in all study sites except in mosquitoes collected in Kaélé and Njombé. The Ace-1 (G119S) mutation was detected in high frequencies (>40%) in Kékem and Santchou. Both An. gambiae and An. coluzzii were detected carrying this mutation. The cytochrome P450s gene Cyp6p3 associated with carbamate resistance and the glutathione S-transferase gene Gste2 associated with organophosphate resistance were found to be overexpressed. Genes associated with pyrethroid (Cyp6m2, Cyp9k1, Cyp6p3) and organochlorine (Gste2, Cyp6z1, Cyp6m2) and cuticle resistance (Cyp4g16) were also overexpressed. The rapid spread of resistance to organophosphates and carbamates could seriously compromise future control strategies based on IRS. It is therefore becoming important to assess the magnitude of bendiocarb and malathion resistance countrywide.

Rapid emergence and spread of pyrethroid resistance in Anopheles gambiae populations is among the main factors affecting malaria vector control in Cameroon, but there is still not enough data on the exact pyrethroid resistance status across Cameroon. The present study assessed pyrethroid resistance profile in different eco-epidemiological settings in Cameroon. Susceptibility bioassay tests were performed with F0 An. gambiae females aged three to five days. Mosquito susceptibility to both permethrin and deltamethrin was assessed. Species of the An. gambiae s.l. complex were identified using molecular diagnostic tools. Target site mutations conferring resistance were detected using Taqman assays. Quantitative reverse transcription-real-time PCR (qRT-PCR) 3-plex TaqMan^® assays were used for the quantification of detoxification genes implicated in pyrethroid resistance. An. gambiae, An. coluzzii and An. arabiensis were identified in the different settings. An. gambiae was dominant in Santchou, Kékem, Bélabo, Bertoua and Njombé, while An. coluzzii was abundant in Tibati and Kaélé. High frequencies of the kdr L1014F allele ranging from 43% to 100% were recorded in almost all sites. The L1014S kdr allele was detected at low frequency (4.10–10%) only in mosquito populations from Njombé and Tibati. The N1575Y mutation was recorded in Kaélé, Santchou, Tibati and Bertoua with a frequency varying from 2.10% to 11.70%. Six Cytochrome P450 genes (Cyp6p3, Cyp6m2, Cyp9k1, Cyp6p4, Cyp6z1, and Cyp4g16) were found to be overexpressed in at least one population. Analysis of cuticular hydrocarbon lipids indicated a significant increase in CHC content in mosquito populations from Kaélé and Njombé compared to Kékem, Bélabo and Bertoua populations. The study indicated high pyrethroid resistance across different ecological settings in Cameroon with different profile of resistance across the country. The present situation calls for further actions in order to mitigate the impact of insecticide resistance on vector control measures.

Despite the contribution of secondary vectors to malaria transmission, there is still not enough information on their susceptibility status to insecticides. The present study assesses the resistance profile of Anopheles pharoensis to DDT. WHO tube tests were used to screen mosquito populations collected from the far-north region of Cameroon for susceptibility to 4% DDT. High DDT resistance in An. pharoensis populations from Maga, Simatou and Yangah with mortality rates ranging from 62.79% to 80% was recorded. Direct sequencing (Sanger) of the VGSC gene was undertaken to search for kdr L1014F/S mutations. However, no kdr allele was detected in the resistant samples. We then looked for cuticle alterations and CHC identification and quantitation were undertaken using GC-MS and GC-FID. High production of cuticular hydrocarbon was recorded in the populations of Yangah and Simatou, with 2420.9 ± 265 and 2372.5 ± 225 ng CHCs/mg dry weight, respectively. The present findings are the first ever describing the development of cuticle resistance in An. pharoensis. The data suggest the need to expand surveillance activities on other vector species.

Malaria continues to pose a significant public health challenge in Cameroon, requiring effective prevention strategies. Long-lasting insecticide-treated nets (LLINs) are widely distributed as a key control measure, but their physical integrity and effectiveness need to be monitored. This study aimed to assess the condition and bio-efficacy of LLINs in 2 regions of Cameroon, namely Santchou in the West and Bertoua in the East. The study evaluated LLIN use and care using a structured questionnaire, following World Health Organization (WHO) guidelines for assessing physical integrity. Bio-efficacy was measured using the 3-min WHO cone assay. The results showed that the ownership and usage rates of mosquito nets were 93.91% and 72.70% in Santchou and 60.68% and 41.11% in Bertoua, respectively. In Santchou, 5.26% of LLINs were damaged, with 21.05% rendered unusable while in Bertoua, 29.41% of the used LLINs were damaged with 16.47% unusable. The knockdown rate with field mosquito populations was 65.49% with mortality rate of 61.24% in Bertoua. In Santchou, knockdown rate was 10.23%, and mortality rate 14.97%. The LLINs tested were found highly effective against susceptible strain. These findings urgently require the National Malaria Control Program of Cameroon to improve public awareness on consistent and proper LLIN usage and address the decline in LLIN effectiveness, particularly in cities like Bertoua and Santchou. Targeted interventions should focus on improving LLINs distribution, educating the population on correct usage practices, and implementing regular monitoring of physical integrity and bio-efficacy of insecticide-treated bed nets as these LLINs get degraded.

Vector-based surveillance is crucial for monitoring arboviral diseases such as dengue, chikungunya, yellow fever, and Zika. In Cameroon, data on the distribution and bionomics of Aedes species in medium-sized cities within the equatorial forest region are limited. This study assessed the distribution, larval habitats, and bionomics of immature Aedes spp. stages across four mid-sized cities of southern Cameroon. Larval surveys were conducted from March 2022 to March 2023 in Bertoua, Kribi, Sangmelima, and Abong-Mbang during rainy and dry seasons. Water-holding containers were inspected using the dipping method, and collected larvae and pupae were reared to adults for morphological identification. Entomological indices were used to estimate arboviral transmission risk, and species co-occurrence in larval habitats was recorded. A generalized linear model was used to compare abundance and distribution among sites, seasons, and breeding site. From 758 larval habitats inspected (214 in Bertoua, 213 in Sangmelima, 184 in Kribi, 147 in Abong-Mbang), 3820 mosquitoes belonging to four genera and 11 species were emerged. Aedes spp. mosquitoes were the most abundant (n = 2903), with Aedes albopictus and Aedes aegypti as dominant species that often co-occurred. Seasonal variation in the abundance of all mosquito genera was significant, with peak Aedes spp. abundance in the rainy season (n = 2359; 81.3%). Tires were the most common larval habitats, mostly located within 10 m of human dwellings. Kribi and Bertoua exhibited the highest container, house, and Breteau indices, suggesting high potential risk. The study supports the need for regular vector-based surveillance to control arboviral disease in Cameroon. Such studies could also provide critical information for strengthening integrated vector management.