Spatial distribution of Anopheles gambiae sensu lato larvae in the urban environment of Yaoundé, Cameroon

Abstract

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.

Spatial and temporal distribution of Anopheles mosquito's larvae and its determinants in two urban sites in Tanzania with different malaria transmission levels

“…As also reported elsewhere, this study found that most of the potential breeding habitats were manmade in origin and had higher larval density than natural habitats ( Djamouko-Djonkam et al, 2019 ; Aik et al, 2019 ), this highlights the potential of public health education in controlling mosquito borne diseases by advocating avoidance on creating potential breeding sites. But also, most of the manmade breeding sites tend to cluster around human settlement as observed in this study that more than three quarter of all the potential breeding sites were within less than 100 m from human settlements and they were more likely to have high larval density as compared to those located more than 100 m from human dwelling.…”

Implication of Anopheles funestus in malaria transmission in the city of Yaoundé, Cameroon

“…funestus are permanent or semi-permanent water collections with emergent vegetation [26]. Its presence in the city of Yaoundé may result from the presence of marshland covered with emerging vegetation along the Mfoundi and Mefou rivers [21]. Anopheles funestus is widely distributed across the country [3] and in most rural settings where it has been reported, it may sustain very high levels of malaria transmission [2,7,16,61].…”

“…The diversity of species might result from the high variety of breeding habitats in Mendong compared to Nsam with the presence of puddles, lakes, rivers, and swamps, which could be excellent habitats for a variety of mosquito species [2,4,11,21]. Seasonal fluctuations in the biting densities of An.…”

“…In Cameroon, the city of Yaoundé is one of the largest in the country with a population of approximately three million inhabitants, and it has experienced intense modification of its natural environment throughout the past years. The rapid and spontaneous urbanisation in and around the city centre, with the absence of infrastructure for sanitation and surface water drainage, as well as the colonisation of lowland areas for urban agriculture or housing construction, has favoured the establishment of anophelines in an urban setting [5,21]. In Cameroon, malaria is still a major public health problem affecting approximately 30% of the population annually [51,64], and its prevention relies entirely on the use of insecticide-treated nets (ITNs) and/or long-lasting insecticidal nets (LLINs) [51].…”

Mapping the breeding sites of Anopheles gambiae s. l. in areas of residual malaria transmission in central western Senegal

“…Information on the spatial distribution of mosquito breeding habitats is needed to enable monitoring and targeting of hotspot areas where vector populations are persistent. The development of Geographic Information Systems (GIS) mapping technology provides high-resolution maps of mosquito distribution or transmission risks, which could improve malaria surveillance system [8,9].…”