Mosquitoes and malaria

The discovery of a mosquito that spends most of its time outside could cause problems for malaria control.

In sub-Saharan Africa, malaria kills some 710,000 people each year. The most dangerous form of the disease is caused by a parasite, Plasmodium falciparum, which is transmitted by mosquitoes, mainly of the species Anopheles gambiae. The mosquito larvae live in water, but the adult insects spend much of their time in buildings, where they have human blood. Insecticide sprays, bed nets and access to malaria medication have helped to decrease the number of deaths from malaria.

The newly discovered mosquito group — a subtype of Anopheles gambiae, could be responsible for eradication not being successful. The insects spend their time outside, and then avoid insecticide.

For decades, everybody has thought that the mosquito rests indoors and bites people indoors but collection methods might be wrong. Collecting adult mosquitoes outside is notoriously difficult: traps with artificial bait are inefficient, and using human bait is banned. The aquatic larvae are easier to catch, and they reveal details such as the individual's place of birth. So some larvae were collected and raised to adulthood in the lab.

The scientists tested them for genetic markers and mutations, and compared them with adults caught inside. They found that the indoor insects consisted of two previously known types of Anopheles gambiae. But the outdoor mosquitoes had three distinct types — the two known ones and the previously unknown group. And 58% of new mosquitoes picked up the parasite that transmits malaria, compared with 35% of the indoor mosquitoes.

Extracted from an article by Amy Maxmen in Nature News. Picture by Kenneth Vernick.