High malaria transmission sustained by Anopheles gambiae s.l. occurring both indoors and outdoors in the city of Yaoundé, Cameroon [version 1; referees: 2 approved]

Background: Malaria remains a major public health problem in Cameroon; however, despite reports on the adaptation of anopheline species to urban habitats, there is still not enough information on malaria transmission pattern in urban settings. In the frame of a larval control trial in the city of Yaoundé, we conducted baseline surveys to assess malaria transmission dynamics in this city. Methods: Adult mosquitoes were collected indoors and outdoors using CDC light traps and human landing catches from March 2017 to March 2018 in 30 districts of Yaoundé, Cameroon. Mosquitoes were sorted by genus and identified to the species level using PCR. The TaqMan method and ELISA were used to determine mosquito infection status to Plasmodium. Bioassays were conducted to assess female Anopheles gambiae susceptibility to insecticides. Results: A total of 218,991 mosquitoes were collected. The main malaria vectors were An. gambiae s.l. (n=6154) and An. funestus s.l. (n=229). Of the 1476 An. gambiae s.l. processed by PCR, 92.19% were An. coluzzii and 7.81% An. gambiae. An. funestus s.l. was composed of 93.01% (173/186) An. funestus and 4.84% (13/186) An. leesoni. The average biting rate of anopheline was significantly high outdoor than indoor (P=0.013). Seasonal variation in mosquito abundance and biting rate was recorded. The infection rate by Plasmodium falciparum was 2.13% (104/4893 mosquitoes processed). The annual entomological inoculation rate was found to vary from 0 to 92 infective bites/man/year (ib/m/y). Malaria transmission risk was high outdoor (66.65 ib/m/y) compared to indoor (31.14 ib/m/y). An. gambiae s.l. was found highly resistant to DDT, permethrin and deltamethrin. High prevalence of the West Africa kdr allele 1014F was recorded and this was not found to influence An. gambiae s.l. infection status.   Conclusion: The study suggests high malaria transmission occurring in the city of Yaoundé and call for immediate actions to improve control strategies

Trypanosome infection rates before and during the target intervention in the control area.

Trypanosome infection rates before and during the target intervention in the control area.</p

Patterns of trypanosome infection rates in <i>Glossina palpalis palpalis</i> in intervention and non-intervention areas.

Patterns of trypanosome infection rates in Glossina palpalis palpalis in intervention and non-intervention areas.</p

Boxplot of <i>Glossina palpalis palpalis</i> apparent densities per trap during the vector control operation.

Boxplot of Glossina palpalis palpalis apparent densities per trap during the vector control operation.</p

Study area—Campo, South Cameroun.

Figure designed using the ESRI satellite base map (https://www.arcgis.com/home/webmap/viewer.html?url= = https://server.arcgisonline.com/arcgis/rest/services/World_Imagery/MapServer&source=sd).</p

Summary of the number of flies captured before and during tsetse control in the intervention area.

Summary of the number of flies captured before and during tsetse control in the intervention area.</p

Location and distribution of tiny targets in the intervention area.

Figure designed using the ESRI satellite base map (https://www.arcgis.com/home/webmap/viewer.html?url = https://server.arcgisonline.com/arcgis/rest/services/World_Imagery/MapServer&source=sd).</p

<i>Trypanosoma</i> sp. infection rates before and during the vector control in the intervention area.

Trypanosoma sp. infection rates before and during the vector control in the intervention area.</p

Summary of the number of flies captured in non-intervention area.

Summary of the number of flies captured in non-intervention area.</p

Characterization of the swarming behavior of Anopheles coluzzii and Anopheles gambiae (Diptera: Culicidae) populations in a hybrid zone of Senegal.

Anopheles gambiae and Anopheles coluzzii, often found in sympatry and synchronous, have undergone a premating reproductive isolation across their distribution range. However, in the Western coast of Africa, unexpected hybridization zones have been observed, and little is known about swarming behavior of these cryptic taxa. Here, we characterized the swarming behavior of An. coluzzii and An. gambiae to investigate its role in the high hybridization level in Senegal. The study was conducted in the south and central Senegal during the 2018 rainy season. Mating swarms of malaria vectors were surveyed at sunset and collected using an insect net. Meanwhile, indoor resting populations of malaria vectors were collected by pyrethrum spray catches. Upon collection, specimens were identified morphologically, and then members of the An. gambiae complex were identified at the species level by polymerase chain reaction (PCR). An. gambiae swarmed mainly over bare ground, whereas An. coluzzii were found swarming above various objects creating a dark-light contrast with the bare ground. The swarms height varied from 0.5 to 2.5 m. Swarming starting time was correlated with sunset whatever the months for both species, and generally lasted about 10 min. No mixed swarm of An. gambiae and An. coluzzii was found even in the high hybridization area. These results indicated a premating isolation between An. coluzzii and An. gambiae. However, the high hybridization rate in the sympatric area suggests that heterogamous mating is occurring, thus stressing the need for further extensive studies. [Abstract copyright: © The Author(s) 2023. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: [email protected].