Diverse novel Wolbachia bacteria strains and genera-specific co-infections with Asaia bacteria in Culicine mosquitoes from ecologically diverse regions of Cameroon

Background: The endosymbiotic bacterium Wolbachia infects numerous species of insects and Wolbachia transinfection of Aedes mosquito species is now being used for biocontrol programs as Wolbachia strains can both inhibit arboviruses and invade wild mosquito populations. The discovery of novel, resident Wolbachia strains in mosquito species warrants further investigation as potential candidate strains for biocontrol strategies. Methods: We obtained mosquito specimens from diverse Culicine mosquitoes from Cameroon including ecologically diverse locations in the Central and West Regions. Wolbachia prevalence rates were assessed in addition to the environmentally acquired bacterial species Asaia in major Culicine genera. PCR-based methods were also used with phylogenetic analysis to confirm identities of host mosquito species and Wolbachia strains were classified using multi-locus sequence typing (MLST). Results: We report high Wolbachia prevalence rates for Culicine species, including in a large cohort of Aedes africanus collected from west Cameroon in which 100% of mono-specific pools were infected. Furthermore, co-infections with Asaia bacteria were observed across multiple genera, demonstrating that these two bacteria can co-exist in wild mosquito populations.  Wolbachia strain MLST and phylogenetic analysis provided evidence for diverse Wolbachia strains in 13 different mosquito species across seven different genera.  Full or partial MLST profiles were generated from resident Wolbachia strains in six Culex species ( quinquefasciatus, watti, cinerus, nigripalpus, perexiguus and rima), two Aedes species (africanus and denderensis) and in Mansonia uniformis, Catageiomyia argenteopunctata, Lutzia tigripes, Eretmapodites chrysogaster and Uranotaenia bilineata. Conclusions: Our study provides further evidence that Wolbachia is widespread within wild mosquito populations of diverse Culicine species and provides further candidate strains that could be investigated as future options for Wolbachia-based biocontrol to inhibit arbovirus transmission.

High prevalence of asymptomatic Plasmodium falciparum malaria in Makenene, a locality in the forest-savannah transition zone, Centre Region of Cameroon

Malaria transmission and prevalence is still not well documented across Cameroon particularly in medium-sized cities or localities representing high transit zone. Different risk factors could be associated with persistence malaria transmission such as population movement from high to low transmission settings. A cross-sectional community-based study was carried out to determine malaria prevalence and risk factors in Makenene, a small city in a forest-savannah which is a crossroads between different parts of the country where travellers usually stop-over day and night to rest. Using malaria diagnostic test (mRDTs from SD-BIOLINE) and microscopy (thin and thick blood smears), 406 participants from 237 households were tested for malaria infection. The prevalence of malaria was high irrespective of the detection method: mRDT (41.87%) or microscopy (38.42%). At household level, 46.41% of households had at least one case of malaria with an average of 1.41 infected individuals per household. Parasite density was also high with the majority of infected individuals (64.74%) bearing more than 500 parasites/μl. Only Plasmodium falciparum was found. The chances of being infected with malaria parasites was almost the same for all participants irrespective of the sleeping behavior, bednet usage, house type and environmental factors. The study supports high malaria transmission in the locality and the need for additional studies on vectors bionomics and transmission patterns.

Aedes Mosquito Surveillance Using Ovitraps, Sweep Nets, and Biogent Traps in the City of Yaoundé, Cameroon

Arbovirus diseases represent a significant public health problem in Cameroon and vector surveillance is a key component of prevention strategies. However, there is still not enough evidence of the efficacy of different sampling methods used to monitor Aedes mosquito population dynamic in different epidemiological settings. The present study provides data on the evaluation of ovitraps and different adult sampling methods in the city of Yaoundé and its close vicinity. Entomological surveys were carried out from February 2020 to March 2021 in two urban (Obili, Mvan), two peri-urban (Simbock, Ahala), and two rural (Lendom, Elig-essomballa) sites in the city of Yaoundé. The efficacy of three sampling methods, namely ovitraps, Biogent Sentinel trap, and sweep nets, was evaluated. Different ovitrap indices were used to assess the infestation levels across study sites; a general linear model was used to determine if there are statistical differences between positive ovitraps across ecological zones. A total of 16,264 Aedes mosquitoes were collected during entomological surveys. Ovitraps provided the highest mosquito abundance (15,323; 91.14%) and the highest species diversity. Of the five Aedes species collected, Aedes albopictus (59.74%) was the most commonly recorded in both urban and rural settings. Different Aedes species were collected in the same ovitrap. The ovitrap positivity index was high in all sites and varied from 58.3% in Obili in the urban area to 86.08% in Lendom in the rural area. The egg density index varied from 6.42 in Mvan (urban site) to 13.70 in Lendom (rural area). Adult sampling methods recorded mostly Aedes albopictus. The present study supports high infestation of Aedes species in the city of Yaoundé. Ovitraps were highly efficient in detecting Aedes distribution across study sites. The situation calls for regular surveillance and control of Aedes population to prevent sudden occurrence of outbreaks.

Population knowledge, attitudes and practices towards malaria prevention in the locality of Makenene, Centre-Cameroon

Background

To contribute to the mission of the National Malaria Control Programme (NMCP) and guide future interventions in Cameroon in general, and in Makenene in particular, this study assessed the knowledge, attitudes and practices of the population of Makenene towards the fight against malaria.

Methods

Using a semi-structured questionnaire, a descriptive cross-sectional household community survey was carried out in randomly selected households in Makenene, a locality situated between forest and savannah ecotypes.

Results

Out of the 413 households surveyed, all (100%) claimed to have heard of malaria with over 94% (n = 391) associating disease transmission with mosquito bites. The main mosquito control tools used in the area were mosquito nets (92.25%). The majority of participants had good knowledge (55.93%; n = 231), good practices (71.67%, n = 296) but moderate attitudes (47.94%; n = 198) towards malaria control and fight. Good knowledge and practices were recorded mostly in educated persons including public servants and students. Good attitudes were adopted mostly by public servants and students of secondary and higher levels of education.

Conclusion

In Makenene, the population exhibits good knowledge and practices towards malaria and its control. However, despite high LLINs ownership and use, people still complain about malaria in the area. Control tools should be monitored, repaired or replaced when necessary to support the achievement of the NMCP mission.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04253-z.

Efficacy of Trapping Methods in the Collection of Eretmapodites (Diptera: Culicidae) Mosquitoes in an Afrotropical Rainforest Region, South western Cameroon

Very little data exist on the biology of an afrotropical rainforest mosquito Eretmapodites (Er.) in a world undergoing dramatic changes due to deforestation. The aim was to assess the efficacy of different trapping methods in the collection of Er. mosquito in forested area. This was a longitudinal study involving collection of mosquitoes for over two years. Multiple collection methods (grouped into two categories), were used; i) net baited and un-baited traps to collect adults, ii) techniques that target immature stages subsequently reared to adults. All males were identified by genitalia dissection. Five thousand seven hundred and four mosquitoes representing 11 genera among which 2,334 Er. were identified. Mosquito abundance was highest in the net traps (n = 1276 (56.4%)) and sweep nets (n = 393(17.4%)) respectively. The abundance was highest in green colored net traps (435(34.09%)) with significant value of χ2= 40.000, P < 0.001 and in pigeons baited traps (473 (37.06%)) with significant value of χ2= 42.000, P = 0.003. The diversity ranges from H' = 2.65; DS = 0.84; SR = 24; ACE = 24.77 in sweep net to H' = 0; DS = 0; SR = 1; ACE = 1 in rock pool among males mosquitoes. While for females, H = 1.14; DS = 0.71; SR = 5; ACE = 5.16, in sweep net to H = 0; DS = 0; SR = 1; ACE = 1 in rock pool, tarpaulin, resting cage. Net traps, bamboo pot, and sweep netting are efficient in collecting high abundance of forest mosquitoes in the Talanagaye rainforest.

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.

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 Yaoundé.

Performance assessment of a widely used rapid diagnostic test CareStart™ compared to microscopy for the detection of Plasmodium in asymptomatic patients in the Western region of Cameroon

While malaria remains a serious public health concern, its rapid or prompt diagnosis in remote areas is important in the fight against the disease. The study aimed to evaluate the performance of widely used Rapid Diagnostic Test (RDT) kits for routinely detection of Plasmodium asymptomatic patients. A total of 400 asymptomatic participants of both sexes aged between 1-89 years from Menoua Division (Santchou and Dschang) were tested for malaria infection using both microscopy and CareStart™ RDT. The prevalence of malaria was higher when using the standard gold tool (Microscopy) (26.0%) compared to RDT (21.8%) with a significant difference (P < 0.05). However, a strong agreement was observed between both tests (kappa = 0.883; P < 0.0001). RDT CareStart™ sensitivity and specificity were 83.65% and 100% respectively while the positive predictive value and negative predictive value were 100% and 95.57% respectively. RDT sensitivity increased with parasite density while false negative (40.4%; n = 17) were observed only when parasite density was low (<500 parasites per microliter of blood). RDT kits appear to be good tools in areas where malaria diagnosis through microscopy is not feasible. However, the low sensibility observed when parasite density is low could be a concern.

New species of Culex (Culiciomyia) (Diptera: Culicidae) from Talangaye Forest in Cameroon and descriptions and identification keys for males of the Afrotropical species of the subgenus

Species of Culex (Diptera: Culicidae) belonging to the subgenus Culiciomyia were collected in partially logged areas and in surrounding pristine forest (Talangaye Forest) in the Nguti Subdivision in the South-West Region of Cameroon. Mosquitoes were collected mainly by sweep netting through forest floor vegetation. Morphological species identification of African Culiciomyia relies almost exclusively on the structure of the male genitalia and the shapes of comb scales on the maxillary palpi of males. Other features of males and the habitus of females are largely indistinguishable between the species of this subgenus. In total, seven currently described species and three new species were collected in the forest. The males of the three new species are described and named as Culex apicopilosus Cornel Mayi, sp. n., Culex lanzaroi Cornel Mayi, sp. n. and Culex pseudosubaequalis Cornel Mayi, sp. n. More detailed descriptions of males of the other currently known species that were collected in the Talangaye Forest and pictorial keys to the males of all Afrotropical species of Culiciomyia, including the new species, are provided.

Effect of deforestation on prevalence of avian haemosporidian parasites and mosquito abundance in a tropical rainforest of Cameroon

Habitat change caused by deforestation can modify the interactions of many biotic and abiotic factors, and in turn influence patterns of diseases in wild birds. Whether deforestation directly or indirectly affects the prevalence of avian haemosporidian parasites through their hosts and/or vectors is still not well understood. We sampled understory bird communities (insectivorous, frugivorous, granivorous and nectarivorous birds) and mosquitoes in three habitats showing a gradient of deforestation (pristine forest, fragmented forest, and young palm oil plantation), to assess the effects of habitat changes on avian haemosporidian (Plasmodium and Haemoproteus) prevalence and its relationship to bird feeding guilds and mosquito abundance. Blood samples of 845 individual birds belonging to 85 species and 27 families were collected in the three habitat types and screened using microscopy and PCR. Plasmodium infections were detected in 136 individuals (16.09%) and varied significantly among habitat types while Haemoproteus infections were detected in 98 individuals (11.60%) and did not vary significantly among habitat types. However, the prevalence of Plasmodium and Haemoproteus in bird feeding groups varied significantly among habitats. Nectarivorous and granivorous birds had the highest Plasmodium and Haemoproteus prevalence, respectively. The abundance of mosquitoes varied significantly among habitat types and the prevalence of Plasmodium significantly and positively correlated with mosquito abundance in fragmented forest. This study highlights the importance of host and mosquito determinants in the transmission dynamics of avian Plasmodium and Haemoproteus infections following habitat changes. Selective logging favored an increase in the prevalence of Plasmodium in insectivores, the prevalence of Haemoproteus in nectarivores and the abundance of female mosquitoes while, the establishment of the palm oil plantation favored an increase in the prevalence of Plasmodium in granivores and Haemoproteus in nectarivores. Species feeding behavior is also an important determinant to consider for a better understanding of patterns of parasite infections in a changing environment.

Impact of deforestation on the abundance, diversity, and richness of Culex mosquitoes in a southwest Cameroon tropical rainforest

Deforestation is a major threat to biodiversity but little data exist on how deforestation in real-time affects the overall mosquito species community despite its known role in the transmission of diseases. We compared the abundance and diversity of Culex mosquitoes before and after deforestation along a gradient of three different anthropogenic disturbance levels in a tropical rainforest in southwestern Cameroon. The collections were conducted in unlogged forest (January, 2016), selectively logged forest (January, 2017), and within a young palm plantation (October, 2017) using net traps, sweep nets, resting traps, and dipping for immature stages in water bodies. Mosquitoes were morphologically identified to subspecies, groups, and species. A total of 2,556 mosquitoes was collected of which 1,663 (65.06%) belong to the genus Culex, (n=427 (25.68%) in the unlogged forest; n=900 (54.12%) in the selectively logged forest; and n=336 (20.2%) in the young palm plantation) with a significant difference among the habitats. Diversity and richness of mosquitoes varied significantly among habitats with the highest values found in the selectively logged forest (H=2.4; DS=0.87; S=33) and the lowest value in the unlogged forest (H=1.37; DS=0.68; S=13). The results of this study showed that deforestation affects the abundance and diversity of Culex mosquitoes and favors the invasion of anthropophilic mosquitoes. Higher mosquito abundance and diversity in the selectively logged forest than in the pristine forest is notable and some explanations for these differences are discussed.