Researchers Find Evidence That A. Gambiae Mosquito Is Evolving Into Two Strains, Could Present Challenges For Malaria Control Efforts

The Anopheles gambiae mosquito, "one of the major carriers of the malaria parasite in Sub-Saharan Africa, is evolving in two directions," according to two studies published Thursday in the journal Science, Scientific American's "Observations" blog reports. "Some 247 million people were infected with malaria as of 2008, according to the World Health Organization, and it is implicated in about one million deaths each year," the blog adds (Harmon, 10/21).

"The revelation could present real difficulties in controlling malaria because eradication strategies directed against one mosquito species may not be effective against another, according to the scientists who discovered the genetic differences between the two strains," the Independent reports (Connor, 10/22).

As one of the "top carriers of malaria parasites," researchers have focused much attention on the A. gambiae mosquito, LiveScience/MSNBC.com writes. "In recent years, researchers observed that A. gambiae seemed to be differentiating into two species," according to the article (10/21).

To better understand the differences between the two lineages, a group of researchers from the Imperial College London, the University of Notre Dame, the J. C. Venter Institute, Washington University and the Broad Institute "carr[ied] out the most detailed analysis so far of the genomes of the M and S strains of Anopheles gambiae mosquito, over two studies," according to a Imperial College London press release.

"The first study, which sequenced the genomes of both strains [from colonies collected from Mali], revealed that M and S are genetically very different and that these genetic differences are scattered around the entire genome. ... The work suggested that many of the genetic regions that differ between the M and S genomes are likely to affect mosquito development, feeding behaviour, and reproduction," according to the press release (10/21).

In the other study "researchers compared key genetic differences between these two A. gambiae types (in addition to the Bamako strain, which falls into the S subtype) [from Mali and Cameroon]," the "Observations" blog adds. "Their study found that, based on genetic sites that seemed to have changed the most, the mosquitoes might be diverging in part due to habitat differences" (10/21).

"From our new studies, we can see that mosquitoes are evolving more quickly than we thought and that unfortunately, strategies that might work against one strain of mosquito might not be effective against another," Mara Lawniczak of Imperial College London, lead author of the studies, said, the Press Association/Guardian reports. "It's important to identify and monitor these hidden genetic changes in mosquitoes if we are to succeed in bringing malaria under control by targeting mosquitoes" (10/21).

LiveScience/MSNBC.com elaborates on the differences between the environments where M and S strains appear to thrive, as described by Notre Dame Biologist Nora Besansky, a co-author on the studies: "S seems to prefer breeding in temporary pools and puddles, Besansky said, while M is more adapted to irrigated habitats like rice fields. The difference in environments represents a trade-off. Puddles are light on predators, so S mosquito larvae can expend energy on quick growth without great risk of getting eaten. Exploiting human irrigation, M mosquitoes can grow and breed even in dry areas, but they may have to adapt to avoid predators in these more-permanent environments. For humans, this ecological efficiency is bad news, Besanksy said."

"Because M is able to exploit areas that tend to be drier and seasons that are drier, this has resulted in malaria spreading in both space and time," Besanksy explained (10/21).

"Future research will further investigate these emerging species, exploring how they compete with one another in various habitats and the molecular basis of their evolution. The results will be used to refine existing malaria interventions and inform the development of new disease prevention strategies," according to an NIH/National Institute of Allergy and Infectious Diseases (NIAID) press release. The studies were funded, in part, by the NIAID (10/21).