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 Specific research studies Entomology
Some new discoveries on mosquito

Mosquito Known to Transmit Malaria Has Been Detected in Ethiopia for the First Time

A type of mosquito that transmits malaria has been detected in Ethiopia for the first time, and the discovery has implications for putting more people at risk for malaria in new regions, according to a study led by a Baylor University researcher.

The mosquito,Anopheles stephensi,normally is found in the Middle East, Indian Subcontinent and China. Previous research shows that more than 68 percent of Ethiopia?s population is at risk for malaria, with an average of 2.5 million cases reported annually, according to the World Malaria Report of 2017.

"From a public health standpoint, or that mosquito populations are increasing where they were o­nce were scarce," said researcher Tamar Carter, Ph.D., assistant professor of tropical disease biology in Baylor?s College of Arts & Sciences, who led the lab work and genetic analysis that led to the identification of the species.

?If these mosquitoes carry malaria, we may see an emergence of malaria in new regions,? she said.

More studies are needed to determine how effective theAnopheles stephensiis in delivering a single-celled parasite that can trigger different forms of malaria, according to the research article Anopheles stephensii carries malaria parasites in Ethiopia," Carter said. "We also need to investigate how theAnopheles stephensigot to Ethiopia and other parts of the Horn of Africa. The question I am particularly interested in is ifAnopheles stephensiis a relatively recent introduction or something that has been flying under the radar in Ethiopia for a long time.

"Clarifying this will help guide better mosquito control efforts in Ethiopia,? she said. ?We plan to use genomic techniques to study the history ofAnopheles stephensiin Ethiopia. More research is needed o­n the feeding and breeding behavior of the EthiopianAnopheles stephensi,and how well it responds to insecticides, to determine best ways to control the mosquito population."

If the mosquito?s propensity for feeding indoors is observed in Ethiopia, different malaria control strategies may need to be implemented, such as insecticide-treated bed nets and indoor residual insecticide spraying.

Throughout November and December 2016, researchers from Jigjiga University in Ethiopia, led by co-first-author Solomon Yared of Jigjiga, collected mosquito larvae and pupae from water reservoirs in Kebri Dehar, an eastern Ethiopian city with a population of 1.3 million, in the Ethiopian Somali Regional State. These larvae were reared to adulthood. Subsequent review of the morphological data confirmed findings from the genetic analysis.

Kebri Dehar has an estimated population of 100,191 ? 51,327 men and 48,864 women, according to figures from the Ethiopian Central Statistical Agency in 2007.

The highest levels of malaria transmission are observed in the north, west and eastern lowland of Ethiopia, according to the research article. Malaria transmission exhibits a seasonal and unstable pattern there, varying with altitude and rainfall.

The article further states that as the migration of people in search of fertile land for crop production and livestock rearing along the river basin, there is concern that malaria transmission may continue to increase in and outside the region. In the eastern lowlands, such as Afar and the Ethiopian Somali Regional State, malaria is endemic along the rivers, where small-scale irrigation activities are practiced for agricultural purposes.

To date, 44 species and subspecies of anopheline mosquitoes have been documented in Ethiopia, with the predominant malaria type beingAnopheles arabiensis.

To gain better insight into the geographic range ofAnopheles stephensi, the next step is to conduct mosquito surveys in multiple locations throughout Ethiopia, Carter said. Researchers believe the effort should center o­n the eastern portion, where they said information o­n malaria vectors in general is scarce. They said both rural and urban surveys are needed, particularly to investigate the role that livestock presence plays inAnopheles stephensiabundance.

Other researchers were Solomon Yared, Araya Gebresilassie, Mohammed Ibrahim and Seid Mohammed, all of Jigjiga University; and Victoria Bonnell, Lambodhar Damodaran, Karen Lopez and Daniel Janies, all of the University of North Carolina at Charlotte.

*This study was financially supported by Jigjiga University. This project was partially funded by the University of North Carolina at Charlotte Multicultural Postdoctoral Fellowship.

Fighting human disease with birth control ... for mosquitoes

Depending o­n where you live, the buzz of a nearby mosquito can be a nuisance, or it can be deadly. Worldwide, more than 500 million people suffer from diseases transmitted by the blood-feeding insects, including malaria, Dengue Fever, Zika, and West Nile, and nearly a million deaths are attributed to mosquito-borne illnesses each year.

Researchers at the University of Arizona have discovered a protein in mosquitos that is critical to the process of producing viable eggs and could pave the way for "mosquito birth control." When researchers selectively blocked the activity of the protein -- which they named Eggshell Organizing Factor 1, or EOF-1 -- in female mosquitoes, the mosquitos laid eggs with defective egg shells, leading to the death of the embryos inside.

In the report, published in the open access journalPLoS Biologyon Jan. 8, the team showed that EOF-1 exists o­nly in mosquitoes. Therefore, any drug developed to render the protein dysfunctional would o­nly affect mosquitoes and no other organisms.

The team, led by Jun Isoe, a research scientist in the lab of Roger Miesfeld, a UA Distinguished Professor and head of the Department of Chemistry and Biochemistry, is hopeful the approach might offer a way to interrupt mosquito egg formation and reduce mosquito populations in areas of human disease transmission without harming beneficial insects such as honey bees.

"We specifically looked for genes that were unique to mosquitoes and then tested for their functional role in eggshell synthesis," Isoe says. "We think there are other discoveries to be made using this same species-directed approach."

Isoe first used a bioinformatics approach to search for and identify genes that are unique to mosquitoes. None of those genes were previously known with regard to their function. The research team then created small RNA molecules that specifically inhibit each of the proteins the genes code for. Known as RNA interference, or RNAi, the technique works by suppressing messenger RNA molecules that serve as blueprints for proteins.

Focusing o­n the previously identified candidate genes o­ne at a time, the RNAi molecules were injected into female mosquitoes right before a blood meal. o­nly female mosquitoes bite because they need a blood meal to produce eggs; the males visit flowers to drink nectar. o­nce a female mosquito has had a blood meal, her follicles develop and it takes three days to lay eggs.

Each individual mosquito was screened for viable offspring. Out of the 40 mosquito-specific genes the team tested, o­nly o­ne, the EOF-1 gene, was found to disrupt eggshell formation and result in the death of the mosquito embryo.

A female mosquito needs a second blood meal in order to produce next the batch of fertilized eggs. Usually, the effects of RNAi injection last o­nly through o­ne egg-laying cycle, but in the case of EOF-1, the researchers were surprised to find that treated females could no longer produce viable eggs for the rest of their two- to three-week life span, even after three consecutive blood meals.

"This lasting effect makes the EOF-1 protein a very attractive target for drugs," Miesfeld says.

Images obtained through electron microscopy revealed that when mosquitoes are deficient in the EOF-1 protein, the females lay eggs with abnormal-looking egg shells. Although the exact function of the protein remains to be elucidated, Isoe and Miesfeld believe that EOF-1 might act as a master switch at the o­nset of the insects' ability to produce viable eggs in response to a blood meal.

Based o­n these results, the team envisions a strategy using small molecule drugs that selectively interfere with mosquito EOF-1 in areas of the world where mosquito-borne human diseases are prevalent, resulting in eggs that never hatch into larvae.

"We think this strategy may have a much lower chance of harming other organisms than what is being used today," Miesfeld says. "Since the days of DDT, we have known that mosquito population control works to reduce the incidence of human disease. This could be a next-generation tool that could be applied to bed nets and other areas frequented by mosquitoes."

Of the more than almost 3,500 species of mosquitoes buzzing across all continents except Antarctica, three genera stand out as carriers of human disease: Mosquitoes of the genusAedestransmit Yellow Fever, Dengue, Chikungunya and Zika viruses; West Nile virus is spread by Culex mosquitoes; andAnophelesmosquitoes are carriers of malaria. To ensure that disruption of EOF-1 was not specific to lab-bred mosquitoes, Isoe tested it o­n a strain ofAedes aegyptimosquitoes collected from wild populations in the Tucson area and found their eggs to be similarly affected.

"The inhibitors currently available to control mosquitoes have been used for so long that the pests are becoming resistant to them," Miesfeld says. "Our idea is to knock their populations down to a level where you can break the cycle of disease transmission between mosquitoes and humans."

As a first step toward turning the discovery into an application that could be commercialized, the team has filed a provisional patent o­n the species-specific discovery process through the UA's technology transfer office, Tech Launch Arizona.

Imaging and quantitative analysis of insecticide in mosquito net fibers using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)

Insecticide-infused netting plays a vital role in limiting the spread of mosquito-borne diseases, but determining when a net has lost its potency poses a tricky technical challenge. Collaboration between pathologists and analytical scientists in the US has led to a potential solution ? a mass spectrometric method to differentiate between effective and ineffective netting (1).

05/27/2019
(Recapitulated)  

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