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WASHINGTON - The genetic blueprint of the mosquito that spreads yellow and dengue fever is more complex than the one that carries malaria, and scientists are hoping to use the information to find ways to thwart the little killers.
Researchers last week published the genome - a map
of all the DNA - of the mosquito species Aedes aegypti, a connoisseur of human blood that spreads disease in tropical and sub-tropical locales worldwide.
The genome, they said, could guide efforts to develop insecticides or to create genetically engineered versions of this mosquito that are unable or less able to transmit the viruses that cause yellow fever and dengue fever.
It is one of only a handful of insects whose genomes have been laid bare, and the second mosquito species. The genome for Anopheles gambiae, which carries the parasite that causes malaria, was published in 2002. There are about 3500 mosquito species, but these two cause most human misery.
Writing in the journal Science, the researchers said the genome for Aedes is about five times larger than the one for Anopheles. Both have roughly 16,000 genes, they said, but Aedes is loaded up with "junk DNA" and other stuff whose function is unclear.
Aedes can transmit disease-causing viruses as it makes a meal out of human blood.
Yellow fever, common in West and Central Africa and in parts of South America, kills about 30,000 people annually. A vaccine has been around for decades, but the number of people infected has risen in the past 20 years, says the World Health Organisation.
Dengue occurs in about 100 countries in tropical areas of the world and kills about 25,000 people annually. There is no vaccine.
"These are huge global health issues," said Vishvanath Nene of the J Craig Venter Institute in Rockville, Maryland, who led the study.
Mosquitoes first appeared 170 million years ago during the age of dinosaurs. The yellow fever and malaria mosquitoes are believed to have diverged evolutionarily from one another about 150 million years ago.
"They both are very robust, very fit mosquitoes. And they love to feed on human blood," said one of the researchers, David Severson of the University of Notre Dame in Indiana.
"Their physical appearance is quite different and their behaviour is quite different. And as we see with their genome architecture, it's also very different," Dr Severson said.
The Aedes is a small, dark mosquito with white markings and banded legs that originated in Africa. People unwittingly spread it worldwide centuries ago when it hitchhiked on transoceanic voyages.
"Aedes is a beauty," Dr Severson said. "Only an entomologist can love them and say: 'Okay, that's really a good-looking mosquito'."
Aedes aegypti
* Spreads yellow fever and dengue fever (35,000 deaths a year)
* Genetic blueprint: Published last week
Anopheles gambiae
* Spreads malaria (estimated 700,000 deaths a year)
* Genetic blueprint: Known since 1992
- REUTERS