Malaria Infection Increases Attractiveness of Humans to Mosquitoes

Do malaria parasites enhance the attractiveness of humans to the parasite's vector? As such manipulation would have important implications for the epidemiology of the disease, the question has been debated for many years. To investigate the issue in a semi-natural situation, we assayed the attractiveness of 12 groups of three western Kenyan children to the main African malaria vector, the mosquito Anopheles gambiae. In each group, one child was uninfected, one was naturally infected with the asexual (non-infective) stage of Plasmodium falciparum, and one harboured the parasite's gametocytes (the stage transmissible to mosquitoes). The children harbouring gametocytes attracted about twice as many mosquitoes as the two other classes of children. In a second assay of the same children, when the parasites had been cleared with anti-malarial treatment, the attractiveness was similar between the three classes of children. In particular, the children who had previously harboured gametocytes, but had now cleared the parasite, were not more attractive than other children. This ruled out the possibility of a bias due to differential intrinsic attractiveness of the children to mosquitoes and strongly suggests that gametocytes increase the attractiveness of the children

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Could species-focused suppression of Aedes aegypti, the yellow fever mosquito, and Aedes albopictus, the tiger mosquito, affect interacting predators? An evidence synthesis from the literature

The risks of Aedes aegypti and Aedes albopictus nuisance and vector-borne diseases are rising and the adverse effects of broad-spectrum insecticide application have promoted species-specific techniques, such as sterile insect technique (SIT) and other genetic strategies, as contenders in their control operations. When specific vector suppression is proposed, potential effects on predators and wider ecosystem are some of the first stakeholder questions. These are not the only Aedes vectors of human diseases, but are those for which SIT and genetic strategies are of most interest. They vary ecologically and in habitat origin, but both have behaviorally human-adapted forms with expanding ranges. The aquatic life stages are where predation is strongest due to greater resource predictability and limited escape opportunity. These vectors' anthropic forms usually use ephemeral water bodies and man-made containers as larval habitats; predators that occur in these are mobile, opportunistic and generalist. No literature indicates that any predator depends on larvae of either species. As adults, foraging theory predicts these mosquitoes are of low profitability to predators. Energy expended hunting and consuming will mostly outweigh their energetic benefit. Moreover, as adult biomass is mobile and largely disaggregated, any predator is likely to be a generalist and opportunist. This work, which summarizes much of the literature currently available on the predators of Ae. aegypti and Ae. albopictus, indicates it is highly unlikely that any predator species depends on them. Species-specific vector control to reduce nuisance and disease is thus likely to be of negligible or limited impact on nontarget predators. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry

Influence of age and previous diet of Anopheles gambiae on the infectivity of natural Plasmodium falciparum gametocytes from human volunteers

The effect of age and dietary factors of Anopheles gambiae (Diptera: Culicidae) on the infectivity of natural Plasmodium falciparum parasites was studied. Mosquitoes of various ages (1–3, 4–7 and 8–11 day old) and those fed blood (either single or double meals) and sugar meals were experimentally co-infected with P. falciparum gametocytes obtained from different naturally infected human volunteers. On day 7, midguts were examined for oocyst infection to determine whether mosquito age or diets have significant effects on parasite infectivity. The age of the mosquitoes did not significantly influence the oocyst infection rates (χ(2) = 48.32, df = 40, P = 0.172) or oocyst load (# of oocysts/midgut) (P = 0.14) observed. Oocyst load between groups was not significantly different. Similarly, the type of diet (either blood or sugar) did not influence oocyst infection rates (χ(2) = 16.52, df = 19, P = 0.622). However, an increase in oocyst infection rates resulted after previous feeding on double blood meals (35%) compared to single blood meals (25%), with comparable oocyst load. These observations are in agreement with those reported in previous studies suggesting that increased mosquito nutritional reserves resulting from increased dietary resources is favorable for malaria infectivity. This field-based study indicates that vector competence of An. gambiae to natural P. falciparum parasites does not vary with age and that nutritional resources acquired prior to an infectious blood meal plays a crucial role in mosquito-parasite relationships. Abbreviation: / oocyst load: number of oocysts per midgut oocyst infection rates: percent of midguts with oocyst

Diversity in anopheline larval habitats and adult composition during the dry and wet seasons in Ouagadougou (Burkina Faso)

Background: Several cases of malaria are frequently recorded during the dry period in Ouagadougou town (Burkina Faso). This has led to the design of a series of studies focusing on both parasitological and entomological investigations intended to provide relevant health data on the risk of local malaria transmission according to the way of urbanisation. Methods: A cross-sectional entomological survey was carried out in various districts of Ouagadougou in April and October 2006. Adult malaria vectors were collected using CDC traps and indoor insecticide spraying performed in four houses during four consecutive days/nights. Intensive larval sampling was also done in available water ponds throughout the study sites. Results: In April, the anopheline breeding sites consisted only of semi-permanent or permanent swamps located mainly in the two peripheral districts. Despite the presence of anopheline larvae in these breeding sites, less than five Anopheles gambiae s.l. adults were caught by CDC traps and indoor insecticide spraying. In October, additionally to the permanent breeding sites reported in April, some rainfall swamps were also found positive to anophelines. The number of adults' mosquitoes was higher than that collected in April (2 vs 159 in October). Out of 115 larvae of An. gambiae s.l. analysed by PCR in April, 59.1% (68/115) were identified as Anopheles arabiensis, 39.1% (45/115) as An. gambiae M while the S form represented less than 2%. Overall 120 larvae and 86 females were identified by PCR in October as An. gambiae M form (51%) and An. arabiensis (42.2%). The S form represented only 6.8%. The global sporozoite rate recorded was high (6.8%) and did not differ between the districts except in the central district where no positive mosquito was detected. Conclusion: Although only few adults' mosquitoes were actively caught during the driest month, malaria vectors persisted all year long that increases the risk of urban malaria transmission. The distribution of breeding sites and especially the occurrence of malaria vectors were more abundant in the periphery, which is more like that of a rural settlement. The evolution of malaria prevalence and the factors sustaining the risk of transmission in Ouagadougou as well in many African cities during the dry season are discussed

Beer Consumption Increases Human Attractiveness to Malaria Mosquitoes

Background: Malaria and alcohol consumption both represent major public health problems. Alcohol consumption is rising in developing countries and, as efforts to manage malaria are expanded, understanding the links between malaria and alcohol consumption becomes crucial. Our aim was to ascertain the effect of beer consumption on human attractiveness to malaria mosquitoes in semi field conditions in Burkina Faso. Methodology/Principal Findings: We used a Y tube-olfactometer designed to take advantage of the whole body odour (breath and skin emanations) as a stimulus to gauge human attractiveness to Anopheles gambiae (the primary African malaria vector) before and after volunteers consumed either beer (n = 25 volunteers and a total of 2500 mosquitoes tested) or water (n = 18 volunteers and a total of 1800 mosquitoes). Water consumption had no effect on human attractiveness to An. gambiae mosquitoes, but beer consumption increased volunteer attractiveness. Body odours of volunteers who consumed beer increased mosquito activation (proportion of mosquitoes engaging in take-off and up-wind flight) and orientation (proportion of mosquitoes flying towards volunteers' odours). The level of exhaled carbon dioxide and body temperature had no effect on human attractiveness to mosquitoes. Despite individual volunteer variation, beer consumption consistently increased attractiveness to mosquitoes. Conclusions/Significance: These results suggest that beer consumption is a risk factor for malaria and needs to be integrated into public health policies for the design of control measures

Fitness consequences of Anopheles gambiae population hybridization

BACKGROUND: The use of transgenic mosquitoes with parasite inhibiting genes has been proposed as an integral strategy to control malaria transmission. However, release of exotic transgenic mosquitoes will bring in novel alleles along with parasite-inhibiting genes that may have unknown effects on native populations. Thus it is necessary to study the effects and dynamics of fitness traits in native mosquito populations in response to the introduction of novel genes. This study was designed to evaluate the dynamics of fitness traits in a simulation of introduction of novel alleles under laboratory conditions using two strains of Anopheles gambiae: Mbita strain from western Kenya and Ifakara strain from Tanzania. METHODS: The dynamics of fitness traits were evaluated under laboratory conditions using the two An. gambiae strains. These two geographically different strains were cross-bred and monitored for 20 generations to score fecundity, body size, blood-meal size, larval survival, and adult longevity, all of which are important determinants of the vector's potential in malaria transmission. Traits were analysed using pair-wise analysis of variance (ANOVA) for fecundity, body size, and blood-meal size while survival analysis was performed for larval survival and adult longevity. RESULTS: Fecundity and body size were significantly higher in the progeny up to the 20(th )generation compared to founder strains. Adult longevity had a significantly higher mean up to the 10(th )generation and average blood-meal size was significantly larger up to the 5(th )generation, indicating that hybrids fitness is enhanced over that of the founder strains. CONCLUSION: Hybridization of the two mosquito populations used in this study led to increased performance in the fitness traits studied. Given that the studied traits are important determinants of the vector's potential to transmit malaria, these results suggest the need to release genetically modified mosquitoes that have the same or very similar backgrounds to the native populations