Assessing the infectious reservoir of falciparum malaria: past and future

Stone, Will; Gonçalves, Bronner P.; Bousema, Teun; Drakeley, Chris

doi:10.1016/j.pt.2015.04.004

Cited by 88 publications

(94 citation statements)

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“…As not all gametocyte carriers are infectious, studies that correlate gametocyte presence, especially among people whose infections are submicroscopic, with measures of infectiousness to mosquitoes are needed to fully understand the age-specific contribution to infection, particularly in light of the lower average gametocyte density found among school-age children. A recent publication by Stone et al [51] attempted to define the proportion of new mosquito infections transmitted by age, combining such xenodiagnostic data from a number of other studies. Stone et al estimated that school-aged children made up about 40% of the proportion of the population that was infectious, but were the source of more than half of new mosquito infections thanks to adjustments for body size and relative exposure to mosquito biting [51].…”

Section: Discussionmentioning

confidence: 99%

High prevalence of Plasmodium falciparum gametocyte infections in school-age children using molecular detection: patterns and predictors of risk from a cross-sectional study in southern Malawi

Coalson

Walldorf

Cohee

et al. 2016

Malar J

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BackgroundIn endemic areas, many people experience asymptomatic Plasmodium infections, particularly older children and adults, but their transmission contribution is unknown. Though not the exclusive determinant of infectiousness, transmission from humans to mosquitoes requires blood meals containing gametocytes. Gametocytes often occur at submicroscopic densities, challenging measurement in human populations. More sensitive molecular techniques allow better characterization of gametocyte epidemiologic patterns.MethodsApproximately 30 households were selected from each of eight sites in southern Malawi during two cross-sectional surveys. Blood was sampled from 623 people during the dry season and 896 the following rainy season. Among people PCR-positive for Plasmodium falciparum, mature gametocytes were detected by qRT-PCR. Regression models evaluated predictors of gametocyte carriage and density in the total population and among those with PCR-positive infections.ResultsThe prevalence of gametocyte carriage by molecular testing was 3.5% during the dry season and 8.6% during the rainy season, and by microscopy 0.8 and 3.3%, respectively. Nearly half of PCR-positive infections carried gametocytes, regardless of recent symptom status. Among P. falciparum-infected people, only living in unfinished houses and age were significantly associated with gametocyte presence. Infected people in unfinished houses had higher odds of carrying gametocytes (OR 2.24, 95% CI 1.16–4.31), and 31% (95% CI 3–65%) higher gametocyte density than those in finished houses. School-age children (5–15 years), had higher odds than adults (≥16 years) of having gametocytes when infected (OR 2.77, 95% CI 1.47–5.19), but 31% (95% CI 11–47%) lower gametocyte density. Children <5 years did not have significantly higher odds of gametocyte carriage or density when infected than adults.ConclusionsSchool-age children frequently carry gametocytes in communities of southern Malawi and represent an under-recognized reservoir of infection. Malaria elimination strategies should address these frequently asymptomatic reservoirs, especially in highly endemic areas. Improved household construction may also reduce the infectious reservoir.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1587-9) contains supplementary material, which is available to authorized users.

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Section: Discussionmentioning

confidence: 99%

High prevalence of Plasmodium falciparum gametocyte infections in school-age children using molecular detection: patterns and predictors of risk from a cross-sectional study in southern Malawi

Coalson

Walldorf

Cohee

et al. 2016

Malar J

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“…Further research is required to understand how the results might be modified at lower transmission, in less seasonal settings or in settings with declining transmission. Similarly, possible associations of age with the detectability and transmissibility of infections, as well as with exposure to mosquitoes, requires further study 42 . Not all infectious individuals need to be detected and treated to reduce the effective reproduction number to below 1.…”

Section: Discussionmentioning

confidence: 99%

Assessing the impact of next-generation rapid diagnostic tests on Plasmodium falciparum malaria elimination strategies

Slater

Ross

Ouédraogo

et al. 2015

Nature

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128

143

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P lasmodium falciparum malaria was responsible for an estimated 584,000 (range 367,000-755,000) deaths in 2013, most of which occurred in young children in sub-Saharan Africa 1 . Although the burden has reduced in response to global efforts to increase the provision of proven malaria interventions such as insecticide-treated bed nets and access to health care and treatment 1 , it remains high. One of the challenges in reducing malaria transmission is the long duration of infection in the human host, which in semi-immune individuals may persist for a year or more 2 . In particular, although infection often leads to disease in naive individuals, those with sufficient acquired immunity can harbour parasites -and hence be onwardly infectious to mosquitoes -without exhibiting symptoms 3 . One option for speeding the decline in transmission could be to target the asymptomatic reservoir of infection 4 by providing either periodic mass-screen-and-treat (MSAT) programmes, focal MSAT or a reactive strategy in which individuals living in the vicinity of an identified clinical case are screened and treated. However, the extent to which such strategies are able to reduce the infectious reservoir will depend on the extent to which the diagnostic used to identify infected individuals also detects those who are onwardly infectious. Another form of targeting could take place at the population level (for example a village) where mass interventions are deployed if the population prevalence *These authors contributed equally.

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“…However, they can be detrimental to crop production and more dramatically many insects are disease-vectors for plants (herbivores) and for animals (blood-feeding). Mosquitoes for instance, are vectors of several deadly human diseases like malaria, dengue, chikungunya and more recently emerging Zika [1–4]. Billions of human lives are threatened by mosquito-borne diseases especially in tropical and sub-tropical zones.…”

Section: Introductionmentioning

confidence: 99%

Isolation of fungi from dead arthropods and identification of a new mosquito natural pathogen

et al. 2016

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BackgroundInsects are well known vectors of human and animal pathogens and millions of people are killed by mosquito-borne diseases every year. The use of insecticides to target insect vectors has been hampered by the issues of toxicity to the environment and by the selection of resistant insects. Therefore, biocontrol strategies based on naturally occurring microbial pathogens emerged as a promising control alternative. The entomopathogenic fungus Beauveria bassiana is well characterized and have been approved by the United States Environmental Protection Agency as a pest biological control method. However, thousands of other fungi are unexploited and it is important to identify and use different fungi for biocontrol with possibly some vector specific strains. The aim of this study was to identify new fungal entomopathogens that may be used as potential mosquito biocontrol agents.MethodsCadavers of arthropods were collected from pesticide free areas and the fungi associated isolated, cultured and identified. Then the ability of each isolate to kill laboratory insects was assayed and compared to that of B. bassiana.ResultsIn total we have isolated and identified 42 fungal strains from 17 different arthropod cadavers. Twenty four fungal isolates were cultivated in the laboratory and were able to induce sporulation. When fungal spores were microinjected into Drosophila melanogaster, eight isolates proved to be highly pathogenic while the remaining strains showed moderate or no pathogenicity. Then a selection of isolates was tested against Aedes mosquitoes in a model mimicking natural infections. Only one fungus (Aspergillus nomius) was as pathogenic as B. bassiana and able to kill 100 % of the mosquitoes.ConclusionThe obtained results are encouraging and demonstrate the feasibility of this simple approach for the identification of new potential mosquito killers. Indeed, it is essential to anticipate and prepare biocontrol methods to fight the expansion of mosquitoes’ habitat predicted in certain geographical areas in association with the occurring climatic changes.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1763-3) contains supplementary material, which is available to authorized users.

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Assessing the infectious reservoir of falciparum malaria: past and future

Cited by 88 publications

References 88 publications

High prevalence of Plasmodium falciparum gametocyte infections in school-age children using molecular detection: patterns and predictors of risk from a cross-sectional study in southern Malawi

High prevalence of Plasmodium falciparum gametocyte infections in school-age children using molecular detection: patterns and predictors of risk from a cross-sectional study in southern Malawi

Assessing the impact of next-generation rapid diagnostic tests on Plasmodium falciparum malaria elimination strategies

Isolation of fungi from dead arthropods and identification of a new mosquito natural pathogen

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