High malaria transmission sustained by Anopheles gambiae s.l. occurring both indoors and outdoors in the city of Yaoundé, Cameroon

Abstract

<ns4:p> <ns4:bold>Background:</ns4:bold> 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. </ns4:p> <ns4:p> <ns4:bold>Methods:</ns4:bold> 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 <ns4:italic>Plasmodium</ns4:italic> . Bioassays were conducted to assess female <ns4:italic>Anopheles gambiae</ns4:italic> susceptibility to insecticides. </ns4:p> <ns4:p> <ns4:bold>Results:</ns4:bold> A total of 218,991 mosquitoes were collected. The main malaria vectors were An. <ns4:italic>gambiae</ns4:italic> s.l. (n=6154) and <ns4:italic>An. funestus</ns4:italic> s.l. (n=229). Of the 1476 <ns4:italic>An. gambiae</ns4:italic> s.l. processed by PCR, 92.19% were <ns4:italic>An. coluzzii</ns4:italic> and 7.81% <ns4:italic>An. gambiae</ns4:italic> . <ns4:italic>An. funestus</ns4:italic> s.l. was composed of 93.01% (173/186) <ns4:italic>An. funestus</ns4:italic> and 4.84% (13/186) <ns4:italic>An. leesoni</ns4:italic> . 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 <ns4:italic>Plasmodium falciparum</ns4:italic> 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). <ns4:italic>An. gambiae</ns4:italic> s.l. was found highly resistant to DDT, permethrin and deltamethrin. High prevalence of the West Africa <ns4:italic>kdr</ns4:italic> allele 1014F was recorded and this was not found to influence <ns4:italic>An. gambiae</ns4:italic> s.l. infection status. </ns4:p> <ns4:p> <ns4:bold>Conclusion</ns4:bold> : The study suggests high malaria transmission occurring in the city of Yaoundé and call for immediate actions to improve control strategies. </ns4:p>