Detection ofPlasmodium falciparumInfection inAnopheles squamosus(Diptera: Culicidae) in an Area Targeted for Malaria Elimination, Southern Zambia

Abstract

Southern Zambia is the focus of strategies to create malaria-free zones. Interventions being rolled out include test and treat strategies and distribution of insecticide-treated bed nets that target vectors that host-seek indoors and late at night. In Macha, Choma District, collections of mosquitoes were made outdoors using barrier screens within homesteads or UV bulb light traps set next to goats, cattle, or chickens during the rainy season of 2015. Anopheline mosquitoes were identified to species using molecular methods and Plasmodium falciparum infectivity was determined by ELISA and real-time qPCR methods. More than 40% of specimens caught were identified as Anopheles squamosus Theobald, 1901 of which six were found harboring malaria parasites. A single sample, morphologically identified as Anopheles coustani Laveran, 1900, was also found to be infectious. All seven specimens were caught outdoors next to goat pens. Parasite-positive specimens as well as a subset of An. squamosus specimens from either the same study or archive collections from the same area underwent sequencing of the mitochondrial cytochrome oxidase subunit I gene. Maximum parsimony trees constructed from the aligned sequences indicated presence of at least two clades of An. squamosus with infectious specimens falling in each clade. The single infectious specimen identified morphologically as An. coustani could not be matched to reference sequences. This is the first report from Zambia of infections in An. squamosus, a species which is described in literature to display exophagic traits. The bionomic characteristics of this species needs to be studied further to fully evaluate the implications for indoor-targeted vector control.

Novel Insights into Malaria Vector Surveillance in Madagascar Using a Quadrant Enabled Screen Trap (QUEST) and Bloodmeal Detection Assay for Regional Transmission (BLOODART)

“…An infectious mosquito is typically defined as a mosquito with sporozoites in the head/thorax [62], which, due to daily rates of mortality [63], will only be a portion of the mosquitoes with the earlier parasite stages in the gut [64]. All of the mosquito species in our sample have been previously documented with sporozoites in Madagascar [10,14,16–22], and the predominant species observed here, An. coustani , was recently implicated as an important vector of Plasmodium parasites [10] in the region.…”

“…squamosus , and An. mascarensis have all been documented with Plasmodium parasites [16–22]. The relative abundance of these species in conjunction with their malaria transmission potential warrants further investigation.…”

“…mascarensis [10,17,21], and An. squamosus [22] as malaria vectors. While common sampling strategies are biased toward endophilic and endophagic mosquitoes [23], most of these potential Malagasy malaria vectors are both exophagic and exophilic [6,21,24].…”

Implicating Cryptic and Novel Anophelines as Malaria Vectors in Africa

“…Plasmodium infections, albeit in a low number of samples, have been recorded in An. coustani in south-western Ethiopia [112], although neither infections nor mosquito identities were confirmed molecularly, and more recently in southern and eastern Zambia [56,116]. In the latter study three molecularly distinct species of An.…”

“…In an area of southern Zambia targeted as an elimination zone, An. squamosus has recently been recognized as a vector of P. falciparum [116]. Although regional Plasmodium infection rates for this species are very low, suggesting they might have a “negligible” role, infection levels at the household or collection level can be quite high.…”