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September 29, 2010

Researchers Decode Genes of Major Disease-Causing Mosquito

An international team of researchers has deciphered the genetic building blocks of the third major disease causing mosquito, an insect that transmits three different diseases from sub-Saharan Africa all the way to the U.S. state of California.

Culex quinquefasciatus, or more simply the Southern House mosquito, is the third major disease-carrying mosquito to have its DNA decoded.

The mosquito is responsible for three parasitic illnesses -- West Nile virus, a brain infection called encephalitis and lymphatic filariasis, which experts say causes 120 million infections and over 40 million cases of elephantiasis each year.

Filariasis worms infect the lymphatic system, including the pea-sized glands that are part of the body's immune system, and can cause massive swellings of the limbs.

Anopholes gambiae, which transmits the malaria parasite throughout Africa and Asia, was genetically sequenced in 2002, followed in 2007 by Anopholes aegypti (uh-JIP-tie), a mosquito that transmits Yellow and Dengue fever.

Peter Arensburger, a geneticist at the University of California Riverside who did the research with an international team of 69 scientists says the sequencing of the Southern House mosquito's DNA is a critical third piece of a genetic puzzle in a global effort to contain the spread of mosquito-borne illness.

"We will now be able to see what genes all these mosquitoes have in common; these three major groups have in common.  What genes they do not have in common.  And this should help us focus in on strategies to prevent the spread of these diseases," he said.

Culex is both extremely diverse and geographically widespread, spanning the globe from South Africa all the way to the U.S. state of California, breeding in filthy water in drains and cesspools.

Scientists say the House mosquito's catalogue of protein-coding genes is significantly larger than the malaria and Dengue and Yellow fever mosquitoes, perhaps because of its ability to adapt to a wide variety of environments.

Marc Muskavitch, a professor of biology at Boston College, collaborated with gene researchers in Massachusetts. "The Southern House mosquito has this cosmopolitan view of feeding on humans and birds and livestock.  And again that may relate to the greater gene number in ways that we don't understand.  But that's a speculation many of us hold," he said.

Because it is difficult to eradicate birds, experts say diseases carried by Culex can be carried over large geographic areas.

Scientists have so far identified some 40 immune system genes shared by all three groups of mosquitoes.

The University of California's Peter Arensburger says it may be possible to develop a single biological agent against all three species.

"So, if we could develop a pesticide that targeted a particular gene in these mosquitoes or one gene that is expressed by all three mosquitoes we might be able to make pesticides that are much more targeted towards just the mosquitoes we are interested rather than something broad that would kill everything around it," he said.

Two articles describing the genetic sequence of Culex quinquefasciatus is published in the journal Science.