Two strains of the Anopheles gambiae mosquito, the main transmitters of malaria in sub-Saharan Africa, known as M and S strains, have changed so much genetically that they appear to be two separate species, even though they look exactly the same, research led by scientists from Imperial College, London write in an article published in the journal Science. One child is killed every thirty seconds because of Malaria worldwide, and more than 200 million people are infected annually; most of them in Africa.

When developing ways of controlling malaria mosquito populations, such as research into novel insecticides or ways to undermine their reproduction, scientists will have to ensure they take into account efficacy for both strains (or species).

The evolution of these mosquitoes is occurring much more rapidly that people had realized, the researchers explain. Their genetic structure needs to be more closely and regularly monitored so that our control measures can keep up.

Dr George Christophides, who works at the Division of Cell and Molecular Biology at Imperial College London, said:

Malaria is a deadly disease that affects millions of people across the world and amongst children in Africa, it causes one in every five deaths. We know that the best way to reduce the number of people who contract malaria is to control the mosquitoes that carry the disease. Our studies help us to understand the makeup of the mosquitoes that transmit malaria, so that we can find new ways of preventing them from infecting people.

Dr Mara Lawniczak, also from the Division of Cell and Molecular Biology at Imperial College London, added:

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. 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.

The scientists carried out two detailed studies which analyzed the genomes of both the M and S strains of the Anopheles gambiae mosquito. The initial study involved sequencing their genomes. The scientists found that M and S strains are not genetically as similar as they had believed, in fact, they are quite different. Their genetic differences were spread all over their genomes. Prior studies had found some differences, but only in certain hot spots of either genome. The researchers add that the differences probably affect mosquito reproduction, development and feeding habits – meaning, they do not do those things in the same way.

In the second study they examined three different mosquito strains, M, S and Bamako – in large numbers. They looked at 400,000 different parts of their genomes where differences were found to exist and compared them. Their aim was to analyze how the three strains were evolving.

The authors believe the strains are evolving differently due partly to specific environmental factors, such as different predators, larval habitats or pathogens (things that make them ill). They used a high density genotyping array to carry out the “the most detailed genetic analysis of an invertebrate”. The scientists are currently investigating how vulnerable each mosquito strain is to specific pathogens, and attempting to link this to their differences in genome makeup. This involves using a specially designed genotyping chip.

The two studies include scientists from Imperial College London (UK), the University of Notre Dame, Indiana (USA), the J.C. Venter Institute, Maryland (USA), Washington University (USA), and the Broad Institute, Cambridge (USA), Institut de Recherche pour le Développement, Unité de Recherche, Montpellier (France), Organisation de Coordination pour la Lutte contre les Endémies en Afrique Centrale, Yaounde (Cameroon), Harvard School of Public Health, Boston (USA), and Boston College (USA).

“SNP Genotyping Defines Complex Gene-Flow Boundaries Among African Malaria Vector Mosquitoes”
D. E. Neafsey, M. K. N. Lawniczak,, D. J. Park, S. N. Redmond, M. B. Coulibaly, S. F. Traoré, N. Sagnon, C. Costantini, C. Johnson, R. C. Wiegand, F. H. Collins, E. S. Lander, D. F. Wirth, F. C. Kafatos, N. J. Besansky, G. K. Christophides, M. A. T. Muskavitch
Science 22 October 2010: Vol. 330. no. 6003, pp. 514 – 517
DOI: 10.1126/science.1193036

Written by Christian Nordqvist