Susceptibility of primary, secondary and suspected vectors to Plasmodium vivax and Plasmodium falciparum infection in Ethiopia

Abstract

Background Insecticide-based vector control interventions in combination with case management with artemisinin-based combination therapy has reduced malaria incidence and prevalence worldwide. Current control methods focus on the primary malaria vectors, Anopheles gambiae sensu lato (s.l.) and the An. funestus group; however, the impact of secondary and suspected vectors has been either sidelined or received limited attention. Defining the susceptibility of secondary, suspected vector species to different parasites in time and space is essential for efficient malaria control and elimination programs. The aim of this study was to assess the susceptibility of An. gambiae s.l., An. coustani complex and An. pharoensis to Plasmodium vivax and P. falciparum infection in Ethiopia. Methods Larvae of Anopheles spp. were collected from different aquatic habitats and reared to adults under laboratory conditions, with the temperature and humidity maintained at 27 ± 1 °C and 75 ± 5%, respectively. Adult female mosquitoes were identified to species as An. gambiae s.l., An. coustani complex and An. pharoensis. Females of these three Anopheles spp. were allowed to feed in parallel feeding assays on infected blood containing the same gametocytes isolated from P. falciparum and P. vivax gametocyte-positive patients by indirect membrane feeding assays. All blood-fed mosquitoes were held under laboratory conditions. After 7 days, all surviving mosquitoes were dissected to detect mid-gut oocyst and enumerated under a microscope. Results Of 5915 female Anopheles mosquitoes exposed to gametocyte-infected blood, 2106 (35.6%)s fed successfully in the 32 independent infection experiments. There was a significant variation in feeding rates among An. gambiae s.l., An. pharoensis and An. coustani complex (G-test = 48.43, P = 3.049e-11). All three exposed mosquito species were receptive to P. vivax and P. falciparum infection development. The percentage of infected mosquitoes following feeding on an infected blood meal was significantly different among species (G-test = 6.49, P = 0.03886). The median infection intensity (II) for An. coustani complex, An. gambiae s.l. and An. pharoensis was 1.16, 2.00 and 1.25, respectively. Although the proportion of infected mosquitoes significantly differed in terms of II, infection rate (IR) and mean oocyst density among the species, mean oocyst density and IR were highly correlated with gametocyte density in all tests (P < 0.001). Conclusion Primary, secondary and suspected vectors were experimentally susceptible to both P. vivax and P. falciparum infection. An effective malaria elimination program might include surveillance and control tools which target secondary and suspected vectors that might play an outdoor transmission role, possibly resulting in reduced focal malaria transmission. Graphical Abstract

Spatiotemporal distribution and bionomics of Anopheles stephensi in different eco-epidemiological settings in Ethiopia

“…pharoensis and An. funestus have been reported to be secondary or suspected malaria vectors in Ethiopia [ 66 ]. We detected An.…”

Bionomics, seasonal abundance and insecticide susceptibility of Anopheles (Diptera: Culicidae) in low and high malaria transmission settings in Ethiopia

“…For instance, recent unpublished data from circumsporozoite enzyme-linked immunosorbent assay (CSP-ELISA) and an artificial infection experiment using a membrane feeding assay showed that Ethiopian populations of An. coustani is susceptible to both Plasmodium falciparum and P. vivax [28]. Molecular species identification was conducted only for pyrethroid resistant samples…”

“…For instance, recent unpublished data from circumsporozoite enzyme-linked immunosorbent assay (CSP-ELISA) and an artificial infection experiment using a membrane feeding assay showed that Ethiopian populations of An. coustani is susceptible to both Plasmodium falciparum and P. vivax [28]. However, there is a paucity of information on the bionomics, seasonal abundance, insecticide susceptibility status and vectorial capacity of secondary and suspected vectors in Ethiopia.…”

Bionomics, seasonal dynamics and insecticide susceptibility of Anopheles mosquitoes in low and high malaria transmission settings of Ethiopia

“…Though secondary malaria vectors are considered to play minor roles in malaria transmission [3], their potential vectorial capacity and competence vary according to locality and season [4]. However, studies on the role of secondary and suspected vectors are limited or entirely missing in Ethiopia, possibly due to the extremely low infection rate (IR) or because no infections were reported [5][6][7].…”

“…Arti cial infection experiment using membrane feeding assay showed the Ethiopian populations of An. coustani is susceptible to both Plasmodium falciparum and P. vivax [7].…”