Differential Plasmodium falciparum infection of Anopheles gambiae s.s. molecular and chromosomal forms in Mali

Abstract

BackgroundAnopheles gambiae sensu stricto (s.s.) is a primary vector of Plasmodium falciparum in sub-Saharan Africa. Although some physiological differences among molecular and chromosomal forms of this species have been demonstrated, the relative susceptibility to malaria parasite infection among them has not been unequivocally shown. The objective of this study was to investigate P. falciparum circumsporozoite protein infection (CSP) positivity among An. gambiae s.s. chromosomal and molecular forms.MethodsWild An. gambiae from two sites Kela (n = 464) and Sidarebougou (n = 266) in Mali were screened for the presence of P. falciparum CSP using an enzyme-linked immunosorbent assay (ELISA). Samples were then identified to molecular form using multiple PCR diagnostics (n = 713) and chromosomal form using chromosomal karyotyping (n = 419).ResultsOf 730 An. gambiae sensu lato (s.l.) mosquitoes, 89 (12.2%) were CSP ELISA positive. The percentage of positive mosquitoes varied by site: 52 (11.2%) in Kela and 37 (13.9%) in Sidarebougou. Eighty-seven of the positive mosquitoes were identified to molecular form and they consisted of nine Anopheles arabiensis (21.4%), 46 S (10.9%), 31 M (12.8%), and one MS hybrid (14.3%). Sixty of the positive mosquitoes were identified to chromosomal form and they consisted of five An. arabiensis (20.0%), 21 Savanna (15.1%), 21 Mopti (30.4%), 11 Bamako (9.2%), and two hybrids (20.0%).DiscussionIn this collection, the prevalence of P. falciparum infection in the M form was equivalent to infection in the S form (no molecular form differential infection). There was a significant differential infection by chromosomal form such that, P. falciparum infection was more prevalent in the Mopti chromosomal forms than in the Bamako or Savanna forms; the Mopti form was also the most underrepresented in the collection. Continued research on the differential P. falciparum infection of An. gambiae s.s. chromosomal and molecular forms may suggest that Plasmodium – An. gambiae interactions play a role in malaria transmission.

Plasmodium falciparum infection rates for some Anopheles spp. from Guinea-Bissau, West Africa

“…The CSP positive rate was significantly higher in A. gambiae (12.6%) than A. coluzzii (4.3%) (Wilcoxon rank sum test P-value=0.0384). This is consistent with the earlier study in Senegal ( Ndiath et al , 2011) but differs from a recent survey conducted in Mali ( Fryxell et al , 2012). The study site in Senegal located in the village of Dielmo (13°43'N, 16°24'W) ( Ndiath et al , 2012)) was geographically closer (200km) than Mali sites (>800km) to our collection sites in Guinea-Bissau.…”

Evidence for Population-Specific Positive Selection on Immune Genes ofAnopheles gambiae

“…The epidemiological importance of GOUNDRY is not currently known, although in experimental infections, this population is physiologically more permissive than M or S form A. gambiae to infection with P. falciparum (Riehle et al 2011). Because the M and S molecular forms are both primary malaria vectors in sub-Saharan Africa, and rates of natural P. falciparum infection in wild M and S mosquitoes are equivalent (Wondji et al 2005; Ndiath et al 2008; Trout Fryxell et al 2012), Plasmodium-driven selective pressure, if it exists, should be shared among these subgroups. However, in our data, only 1 of the 11 signals of positive selection (that at APL1B ) was shared by two subpopulations (Figure 3), and we found no evidence of non-neutral evolution in any genes in the S-form population.…”

Application of a qPCR Assay in the Investigation of Susceptibility to Malaria Infection of the M and S Molecular Forms of An. gambiae s.s. in Cameroon

“…M/S hybrids are rarely observed in natural settings but several recent studies reported levels of hybridization higher than expected for cryptic species [19], [20], [22], [59], [62], [63], [64] ). Subgroups of An.…”

“…Out of the 400 described Anopheles species, less than 20 are capable of transmitting malaria parasites [58]. Some species are more susceptible to Plasmodium infection than others, and even at the population level, their susceptibility differs [21], [22], [59]. The respective role of the different vectors in malaria transmission needs to be clarified, and our assay will be useful to provide accurate estimation of the entomological inoculation rate (EIR) of each vector species or populations; EIR being the key parameter to measure malaria transmission intensity in endemic areas.…”

“…In the wild, the M and S forms colonize different ecological niches, the S form being more adapted to arid environments, but the two forms can also be found in sympatry [19], [20]. The relative susceptibility of the M and S forms to malaria infection has been poorly investigated and gave rise to different results, in Senegal the S form was more susceptible than the M one, but no difference between the two forms was observed in Mali [21], [22]. Further studies are needed at larger scale to identify genetic and/or ecological factors that determine transmission by natural vector populations; this has important implications to target vector control.…”