Deletions of the Plasmodium falciparum hrp2 and hrp3 genes can affect the performance of HRP2-based malaria rapid diagnostic tests (RDTs). Such deletions have been reported from South America, India and Eritrea. Whether these parasites are widespread in East Africa is unknown. A total of 274 samples from asymptomatic children in Mbita, western Kenya, and 61 genomic  data from Kilifi, eastern Kenya, were available for analysis. PCR-confirmed samples were investigated for the presence of pfhrp2 and pfhrp3 genes. In samples with evidence of deletion, parasite presence was confirmed by amplifying three independent genes. We failed to amplify pfhrp2 from 25 of 131 (19.1%) PCR-confirmed samples. Of these, only 8 (10%) samples were microscopic positive and were classified as pfhrp2-deleted. Eight microscopically-confirmed pfhrp2-deleted samples with intact pfhrp3 locus were positive by HRP2-based RDT. In addition, one PCR-confirmed infection showed a deletion at the pfhrp3 locus. One genomic sample lacked pfhrp2 and one lacked pfhrp3. No sample harbored parasites lacking both genes. Parasites lacking pfhrp2 are present in Kenya, but may be detectable by HRP-based RDT at higher parasitaemia, possibly due to the presence of intact pfhrp3. These findings warrant further systematic study to establish prevalence and diagnostic significance.

Malaria parasites () can change the attractiveness of their vertebrate hosts to vectors, leading to a greater number of vector-host contacts and increased transmission. Indeed, naturally-infected children have been shown to attract more mosquitoes than parasite-free children. Here, we demonstrate -induced increases in the attractiveness of skin odor in Kenyan children and reveal quantitative differences in the production of specific odor components in infected vs. parasite-free individuals. We found the aldehydes heptanal, octanal, and nonanal to be produced in greater amounts by infected individuals and detected by mosquito antennae. In behavioral experiments, we demonstrated that these, and other,-induced aldehydes enhanced the attractiveness of a synthetic odor blend mimicking "healthy" human odor. Heptanal alone increased the attractiveness of "parasite-free" natural human odor. Should the increased production of these aldehydes by -infected humans lead to increased mosquito biting in a natural setting, this would likely affect the transmission of malaria.

Abstract. The host preferences of the anthropophilic mosquito species in the Anopheles gambiae complex (Diptera: Culicidae) are mediated by skin bacterial volatiles. However, it is not known whether these mosquitoes respond differentially to skin bacterial volatiles from non-human host species. In this study, the responses of two malaria mosquito species in the An. gambiae complex, Anopheles gambiae s.s. (hereafter, An. gambiae) and Anopheles arabiensis, with different host preferences, to volatiles released from skin bacteria were tested. Skin bacteria collected from human, cow and chicken skin significantly increased trap catches; traps containing bacteria collected from human skin caught the highest proportions of An. gambiae and An. arabiensis. Traps with bacteria of human origin caught a significantly higher proportion of An. gambiae than of An. arabiensis, whereas bacterial volatiles from the chicken attracted significantly higher numbers of An. arabiensis than of An. gambiae. Additionally, An. gambiae showed a specialized response to volatiles from four specific bacteria, whereas An. arabiensis responded equally to all species of bacteria tested. Skin bacterial volatiles may therefore play important roles in guiding mosquitoes with different host preferences. The identification of these bacterial volatiles can contribute to the development of an odour blend that attracts mosquitoes with different host preferences.

It has been suggested that Plasmodia manipulate their vertebrate hosts to enhance parasite transmission. Using a dual-choice olfactometer, we investigated the attraction of Anopheles gambiae to 50 Kenyan children (aged 5-12 years) who were naturally infected with Plasmodium falciparum or noninfected controls. Microscopic gametocyte carriers attracted almost 2 times more mosquitoes than children who were parasite free, harbored asexual stages, or had gametocytes at submicroscopic densities. By using highly sensitive stage-specific molecular methods to detect P. falciparum, we show that gametocytes-and not their noninfectious asexual progenitors-induce increased attractiveness of humans to mosquitoes. Our findings therefore support the parasite host manipulation hypothesis.

BackgroundThe anthropophilic malaria mosquito Anopheles gambiae sensu stricto (hereafter termed Anopheles gambiae) primarily takes blood meals from humans, whereas its close sibling Anopheles arabiensis is more opportunistic. Previous studies have identified several compounds that play a critical role in the odour-mediated behaviour of An. gambiae. This study determined the effect of natural and synthetic odour blends on mosquitoes with different host preferences to better understand the host-seeking behaviour of mosquitoes and the potential of synthetic odour blends for standardized monitoring.MethodsOdour blends were initially tested for their attractiveness to An. gambiae and An. arabiensis in a semi-field system with MM-X traps baited with natural and synthetic odours. Natural host odours were collected from humans, cows and chickens. The synthetic odour blends consisted of three or five previously identified compounds released with carbon dioxide. These studies were continued under natural conditions where odour blends were tested outdoors to determine their effect on species with different host preferences.ResultsIn the semi-field experiments, human odour attracted significantly higher numbers of both mosquito species. However, An. arabiensis was also attracted to cow and chicken odours, which confirms its opportunistic behaviour. A five-component synthetic blend was highly attractive to both mosquito species. In the field, the synthetic odour blend caught significantly more An. funestus than traps baited with human odour, while no difference was found for An. arabiensis. Catches of An. arabiensis and Culex spp. contained large numbers of blood-fed mosquitoes, mostly from cows, which indicates that these mosquitoes had fed outdoors.ConclusionsDifferent odour baits elicit varying responses among mosquito species. Synthetic odour blends are highly effective for trapping mosquitoes; however, not all mosquitoes respond equally to the same odour blend. Combining fermenting molasses with synthetic blends in a trap represents the most effective tool to catch blood-fed mosquitoes outside houses, which is essential for understanding outdoor malaria transmission.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0635-1) contains supplementary material, which is available to authorized users.

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Most malaria-endemic countries are heavily reliant upon rapid diagnostic tests (RDT) for malaria case identification and treatment. RDT previously used for malaria diagnosis can subsequently be used for molecular assays, including qualitative assessment of parasite species present or the carriage of resistance markers, because parasite DNA can be extracted from the blood inside the RDT which remains preserved on the internal components. However, the quantification of parasite density has not previously been possible from used RDT. In this study, blood samples were collected from school-age children in Western Kenya, in the form of both dried blood spots on Whatman filter paper, and the blood spot that is dropped into rapid diagnostic tests during use. Having first validated a robotic DNA extraction method, the parasite density was determined from both types of sample by duplex qPCR, and across a range of densities. The methods showed good agreement. The preservation of both parasite and human DNA on the nitrocellulose membrane inside the RDT was stable even after more than one year’s storage. This presents a useful opportunity for researchers or clinicians wishing to gain greater information about the parasite populations that are being studied, without significant investment of resources.

BackgroundArtemisinin-based combination therapy (ACT) is the recommended treatment against uncomplicated Plasmodium falciparum infections, and ACT is widely used. It has been shown that gametocytes may be present after ACT and transmission to mosquitoes is still possible. Artemether–lumefantrine (AL) is a broadly used artemisinin-based combination medicine. Here, it is tested whether AL influences behaviour and fitness of Anopheles mosquitoes, which are the main vectors of P. falciparum.ResultsDual-choice olfactometer and screenhouse experiments showed that skin odour of healthy human individuals obtained before, during and after AL-administration was equally attractive to Anopheles coluzzii and Anopheles gambiae sensu stricto, apart from a small (but significant) increase in mosquito response to skin odour collected 3 weeks after AL-administration. Anopheles coluzzii females fed on parasite-free blood supplemented with AL or on control-blood had similar survival, time until oviposition and number of eggs produced.ConclusionsBased on the results, AL does not appear to influence malaria transmission through modification of vector mosquito olfactory behaviour or fitness. Extending these studies to Plasmodium-infected individuals and malaria mosquitoes with parasites are needed to further support this conclusion.Electronic supplementary materialThe online version of this article (10.1186/s12936-019-2646-9) contains supplementary material, which is available to authorized users.