Abstract
BackgroundRapid demographic growth in Douala city, Cameroon, has resulted in profound ecological and environmental changes. Although demographic changes can affect anopheline mosquito breeding sites, there is a lack of understanding about the epidemiological impact that such changes might have on vector ecology and malaria transmission.MethodsA 12-month entomological study was conducted in a highly populated district of Douala called Ndogpassi. Adult mosquitoes were collected using two methods: 1) human landing catches (HLC); and 2) Centers for Disease Control and Prevention (CDC) light traps; these methods were used twice monthly from January to December 2011. Mosquito genus and species were identified with morphological and molecular diagnostic tools. The sampling efficiency of the CDC light trap and HLC were compared. Anopheles gambiae infection with Plasmodium falciparum was detected using ELISA. Susceptibility to DDT, permethrin, and deltamethrin insecticides were also determined.ResultsA total of 6923 mosquitoes were collected by HLC (5198) and CDC light traps (1725). There was no equivalence in the sampling efficiency between light traps and human landing catches (P > 0.01). With 51% of the total, Culex was the most common, followed by Anopheles (26.14%), Mansonia (22.7%) and Aedes (0.1%). An. gambiae ss (M form) comprised ~98% of the total anophelines collected. An. gambiae had a biting rate of 0.25 to 49.25 bites per human per night, and was the only species found to be infected with P. falciparum. A P. falciparum infection rate of 0.5% was calculated (based on enzyme-linked immunosorbent assays using the circumsporozoite surface protein). The entomological inoculation rate was estimated at 31 infective bites per annum. Insecticide susceptibility tests on An. gambiae females revealed a mortality rate of 33%, 76% and 98% for DDT, permethrin and deltamethrin, respectively. The West African kdr allele (L1014F) was detected in 38 of the 61 An. gambiae analyzed (62.3%).ConclusionsThe present study revealed seasonal malaria transmission in Douala. High levels of An. gambiae were detected along with a high prevalence of insecticide resistance in this vector population. These findings highlight the need to promote use of insecticide-impregnated bed nets in Douala.
Highlights
Rapid demographic growth in Douala city, Cameroon, has resulted in profound ecological and environmental changes
Unplanned urbanization characterized by poor housing, lack of sanitation and inadequate surface water drainage is recognized as one of the major factors maintaining the presence of Anopheles gambiae in some urban settings [2], it has not been extensively studied in Cameroon
For molecular identification of the An. gambiae M and S forms, an average of 20 to 40 mosquitoes were randomly selected from those collected each month using both Human landing catches (HLC) and Centers for Disease Control and Prevention (CDC) light traps (LT) methods
Summary
Rapid demographic growth in Douala city, Cameroon, has resulted in profound ecological and environmental changes. Some reports indicate that the rapid demographic growth of some urban areas presents a serious challenge for the control of endemic diseases such as malaria [1,2]. Douala is a port city close to the Atlantic Ocean with year-round rainfall and a high level of spontaneous urbanization compared with Yaoundé, which is situated inland at high altitude. All this making that Yaoundé and Douala could experience distinctive malaria epidemiological conditions. Better understanding of the factors affecting malaria epidemiology in Douala could assist efforts towards malaria control in the city
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