Sequences characterized of new viruses that infect Anopheles gambiae

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West African Anopheles gambiae mosquitoes harbor a taxonomically diverse virome including new insect-specific flaviviruses, mononegaviruses, and totiviruses

Text by Mark D. Stenglein

Entomologist Johann Wilhelm Meigen named the Anopheles genus of mosquitoes after a Greek word meaning “useless” or “harmful”. True to their name, anopheles mosquitoes are a global scourge, responsible for transmitting malaria and other serious diseases. Despite their public health importance, few studies have characterized viruses that naturally infect these mosquitoes. In this study, we characterized viruses from Anopheles gambiae and related mosquitoes from 3 malaria-endemic countries in West Africa.  We identified a number of new virus sequences, performed analyses comparing them to known viruses, and measured their prevalence in wild populations.

One challenge we faced is that it is easier to identify a new virus sequence than it is to convert this information into biological understanding. For example, we identified a new totivirus sequence. But we could not conclude that that this virus even infects mosquitoes. In fact, totiviruses are best known as viruses of plants and fungi and this virus might actually infect fungi associated with mosquitoes or might have been present in plant nectar upon which these mosquitoes fed. Nevertheless, we endeavored to gain as much insight as we could into the new virus sequences using computational and comparative methods. For example, we analyzed dinucleotide composition to provide evidence that the new flavivirus we discovered is a genuine mosquito virus. Ultimately, however, to quote virologist Vincent Racaniello, metagenomics only gets you so far, and “experiments need to be done”. So we are pushing forward with experiments to better understand these new viruses and any possible impact on mosquito physiology.

Another technical challenge we faced is attributable to a common practice in vector-borne disease surveillance: sample pooling. Pooling has its advantages: it’s cheaper and faster to process fewer samples, and if mosquitoes only rarely carry a particular human pathogen (e.g. as is the case for West Nile virus), then pooling increases the sensitivity of surveillance.  But pooling has its drawbacks.  Some of our pools contained the sequences of multiple related viruses. Disentangling these similar but not identical sequences is challenging. And, with pooling you only get coarse-grained measures of prevalence. You also lose information about relationships between the abundances of different organisms in individual mosquitoes. After all, one motivation for our study was to identify commensal anopheles viruses that could alter their vector competence. The averaging effect of pooling washes out this signal. But in any case, we did identify intriguing new viruses and we look forward to learning more about them.

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Mosquito collection sites in Liberia, Senegal, and Burkina Faso. In Liberia, mosquitos were sampled from 6 villages within an area with an approximate radius of 16 km. The collection site in Burkina Faso for mosquito eggs that were used to found a laboratory colony is indicated.

Introducing the authors

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Left panel: Study authors postdoc James Weger (leftmost) and PhD student Joseph Fauver (rightmost) working with the mosquito collection team in Lofa County Liberia, August 2015.  Middle: Kpehe Bolay and study author Lawrence Fakoli III collecting mosquitoes in Northern Liberia, March 2015.  Right: Mark Stenglein is an assistant professor in the dept. of Microbiology, Immunology, and Pathology at Colorado State University.

About the research

West African Anopheles gambiae mosquitoes harbor a taxonomically diverse virome including new insect-specific flaviviruses, mononegaviruses, and totiviruses
Joseph R. Fauver, Nathan D. Grubaugh, Benjamin J. Krajacich, James Weger-Lucarelli, Steven M. Lakin, Lawrence S. Fakoli III, Fatorma K. Bolay, Joseph W. Diclaro II, Kounbobr Roch Dabiré, Brian D. Foy, Doug E. Brackney, Gregory D. Ebel, Mark D. Stenglein
Virology, Volume 498, November 2016, Pages 288–299