Researchers hint the origins of one in all nature’s best killers

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One of the world’s leading killer of humans, a species of mosquito originated more than 7 million years ago on islands in the Indian Ocean, some of which had no mammals whatsoever. This emerges from a genetic analysis by Yale researchers published in the August 17th magazine Molecular Ecology.

Disease-borne mosquitoes kill more people each year than war, terrorist attacks and murders. And of the 3,500 mosquito species, Aedes aegypti is one of the deadliest. It transmits viral diseases such as dengue fever, chikungunya, zika and yellow fever, which make or kill tens of millions of people every year. Scientists had previously believed that the species originated in continental Africa and spread to other areas of the world about 500 years ago via the slave trade and the European colonization of Africa.

A Yale team led by Jeffrey Powell, professor of ecology and evolutionary biology, and postdoctoral researcher John Soghigian, now at North Carolina State University, performed a genetic analysis of mosquito species in Africa and the southwestern Indian Ocean. They found that more than 7 million years ago, mosquitos of ancestors resembling Aedes aegypti appeared in Madagascar and the islands in the Indian Ocean.

We estimate the species only arrived in Africa 50,000 to 80,000 years ago, which was a big surprise, ā€said Powell.

A global map with detailed information on regions that will report dengue fever to the World Health Organization from 2014 and overlay the distribution of Aedes aegypti mosquitoes. The latter includes most of Central and South America, all of Africa, South Asia and the Indian subcontinent, as well as most of Australia. Areas reported for dengue include all of Central America, most of South America excluding the South Horn, parts of the coast and Central Africa, Madagascar, India, Southeast Asia, and the North Horn of Australia.

Powell suspects that the mosquito, which normally lays eggs in pools of water that accumulates in rocks or trees, is slowly spreading from east to west Africa. There it adapted to a drier climate and eventually learned to feed on the blood of the growing human population in West African villages where water was stored to withstand extended periods of drought. The mosquito transported by slave traders eventually spread to tropical and subtropical areas around the world.

Yales Andrea Gloria-Soria is co-author of the paper, which included contributions from researchers from the University of Montpellier and the Pasteur Institute in France.

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