Malaria News Today 2020-09-30: Diagnostics, Mosquito Genes and Neutrophils

Mosquito populations vary across nations and can be spurred by change in land use and deforestation as seen in Madagascar. Urine and saliva have potential in diagnostics but have lower sensitivity than blood tests. Not all insects have similar genes, and mosquitoes evolved a different gene to handle body segmentation. The DHS Program has released recent Malaria Indicator Surveys for Ghana and Uganda, but indicators are below targets. The emerging roles for neutrophils in malaria will be discussed at a webinar. Finally cost-effectiveness issues around RDTs is noted. More information can be obtained via the hyperlinks.

Variation in Anopheles distribution and predictors of malaria infection risk across regions of Madagascar

Deforestation and land use change is widespread in Madagascar, altering local ecosystems and creating opportunities for disease vectors, such as the Anopheles mosquito, to proliferate and more easily reach vulnerable, rural populations. Knowledge of risk factors associated with malaria infections is growing globally, but these associations remain understudied across Madagascar’s diverse ecosystems experiencing rapid environmental change. This study aims to uncover socioeconomic, demographic, and ecological risk factors for malaria infection across regions through analysis of a large, cross-sectional dataset.

The presence of aquatic agriculture (both within and surrounding communities) is the strongest predictive factor of habitats containing Anopheles larvae across all regions. Ecological and socioeconomic risk factors for malaria infection vary dramatically across study regions and range in their complexity. Risk factors for malaria transmission differ dramatically across regions of Madagascar. These results may help stratifying current malaria control efforts in Madagascar beyond the scope of existing interventions.

Evaluating the potential of using urine and saliva specimens for malaria diagnosis in suspected patients in Ghana

This study aimed at detecting PfHRP2 and pLDH malaria antigens in urine and salivary specimens of suspected malaria patients using RDT kits, and identifying factors influencing the detection of these antigens. Malaria rapid test kit (SD Bioline RDT kit) was used to detect malaria antigens, PfHRP2 and pLDH, in blood, urine and saliva samples received from patients suspected of malaria. Subsequently, malaria parasitaemia was determined.

A total of 706 suspected malaria patients provided all three specimens. Prevalence of malaria by microscopy and RDT was 44.2% and 53.9%, respectively. Compared to blood, the sensitivities of urine and saliva were 35.2% and 57.0% respectively. Haemoglobin concentration?<?9.9 g/dL, body temperature?>?38.7 °C and occult blood influenced the detection of malaria antigens in both urine and saliva. Furthermore, the antigens were not detected in urine and saliva when parasitaemia was?<?60,000 parasites/µL and?<?40,000 parasites/µL, respectively.

Saliva, with or without blood contamination, was found to be more efficient that urine samples. Therefore these non-blood specimens have the potential to be used as non-invasive samples for malaria diagnosis. However, this approach is useful in severe to moderate anaemia, hyperthermia, parasitaemia?>?60,000 parasites/µL and samples contaminated with blood.

Mosquitos lost an essential gene for body segmentation with no ill effects

University of Maryland entomologists discovered that a gene critical for survival in other insects is missing in mosquitoes—the gene responsible for properly arranging the insects’ segmented bodies. The researchers also found that a related gene evolved to take over the missing gene’s job. Although laboratory studies have shown that similar genes can be engineered to substitute for one another, this is the first time that scientists identified a gene that naturally evolved to perform the same critical function as a related gene long after the two genes diverged down different evolutionary paths.

The work emphasizes the importance of caution in genetic studies that use model animals to make conclusions across different species. It also points to a new potential avenue for research into highly targeted mosquito control strategies. The research study was published in the September 30, 2020, issue of the journal Communications Biology. “Every single arthropod has a segmented body plan. And you would think it develops the same way in all of them. But what we found is that it doesn’t,” said Alys Jarvela. “That means different genes probably regulate male fertility in mosquitoes, and they might be unique to the mosquito, which could potentially provide a powerful avenue for controlling mosquitoes without harming other insects such as butterflies and bees,” Jarvela said.

Two New Malaria Indicator Surveys Available

Ghana 2019 MIS/DHS Infographic. Malaria prevalence going down from 27% in 2014 to 14% in 2019. Still below target in terms of ITN coverage of and in households.

Uganda 2018-19 MIS/DHS Infographic.  Wide regional variation in malaria prevalence from 1-5% in the southwest to 34% in the northeast. ITN use by children and pregnant women below 2/3rds, while only 2/5 pregnant women got 3 doses of IPT.

Emerging Roles for Neutrophils in Malaria

Aubrey Cunnington and an interdisciplinary translational research group studying host-pathogen interactions in severe infections, focussing on malaria in particular. See for example,  “A More Granular View of Neutrophils in Malaria

Neutrophils are abundant innate immune cells with crucial roles in immunity and vascular inflammation. Recent evidence indicates that neutrophils have a dual role in malaria, contributing to both pathogenesis and control of Plasmodium. We discuss emerging mechanisms behind these opposing functions and identify key outstanding questions.

Cost-effectiveness analysis of malaria rapid diagnostic test in the elimination setting

As more and more countries approaching the goal of malaria elimination, malaria rapid diagnostic tests (RDT) was recomended to be a diagnostic strategy to achieve and maintain the statute of malaria free, as it’s less requirements on equipment and expertise than microscopic examination. But there are very few economic evaluations to confirm whether RDT was cost-effective in the setting of malaria elimination. This research aimed to offer evidence for helping decision making on malaria diagnosis strategy.

The results showed that RDT strategy was the most effective (245 cases) but also the most costly (United States Dollar [USD] 4.47 million) compared to using microscopy alone (238 cases, USD 3.63 million), and RDT followed by microscopy (221 cases, USD 2.75 million). There was no strategy dominated. One-way sensitivity analysis reflected that the result was sensitive to the change in labor cost and two-way sensitivity analysis indicated that the result was not sensitive to the proportion of falciparum malaria. The result of Monte Carlo simulation showed that RDT strategy had higher effects and higher cost than other strategies with a high probability. Compared to microscopy and RDT followed by microscopy, RDT strategy had higher effects and higher cost in the setting of malaria elimination.

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