Eukaryotes Genomes - ANOPHELES GAMBIAE

Anopheles gambiae is the principal vector of malaria, a disease that afflicts more than 500 million people and causes more than 1 million deaths each year

Anopheles gambiae is the major vector of Plasmodium falciparum in Africa and is one of the most efficient malaria vectors in the world. Its blood meals come almost exclusively from humans, its larvae develop in temporary bodies of water produced by human activities (e.g., agricultural irrigation or human and animal footprints that have become flooded), and adults rest primarily in human dwellings.

There are about 2,500 species of mosquito in the world but only those of the genus anopheles carry the human malaria parasite. Of the 380 known species of anopheles, about 60 can transmit malaria. And of these 60, Anopheles gambiae is best adapted to spreading the disease.

Females have to suck blood so that they can reproduce, acquiring protein is essential for egg production. The malaria parasite, plasmodium, enters the human body through the mosquito's saliva. In the course of a malaria infection, the parasite digests its human host's haemoglobin. The mosquito repeatedly pierces the victim's skin with her mouthpiece - a pair of sharp, needle-like tubes. With each prick, one tube sends anti-coagulants and other chemicals into the bloodstream so your blood flows freely into her stomach. When she hits a capillary, the other tube sucks up the blood. An engorged mosquito can triple in weight. When another mosquito bites you, it in turn sucks up infected red blood cells.

The female mates only once, storing sperm for all subsequent egg production. Mating is the first activity of the newly-hatched adult. The female needs a blood meal for each batch of eggs she produces and she will lay about 100 eggs in water at two or three day intervals. Eggs take two to three days to hatch. The larvae grow rapidly, passing through three moults in three days.

From egg to adult anopheles takes seven to 21 days, depending on temperature. After two to three days, the adult emerges and after the third moult, the larva becomes a pupa.

The parasite needs to develop in the mosquito for at least eight to ten days before it can infect other people again and this is where the warm, wet conditions of tropical Africa play a decisive role. Because mosquitoes are a cold blooded animal, the speed at which this development takes place directly depends on the temperature.

During the 1950s and early 1960s, the World Health Organization (WHO) malaria eradication campaign succeeded in eradicating malaria from Europe and sharply reduced its prevalence in many other parts of the world, primarily through programs that combined mosquito control with antimalarial drugs such as chloroquine. Sub-Saharan Africa, for the most part, did not benefit from the malaria eradication program, but the widespread availability of chloroquine and other affordable antimalarial drugs no doubt helped to control malaria mortality and morbidity. Unfortunately, with the appearance of chloroquine-resistant malaria parasites and the development of resistance of mosquitoes to the insecticides used to control disease transmission, malaria in Africa is again on the rise. Even control programs based on insecticide-impregnated bed nets, now widely advocated by WHO, are threatened by the development of insecticide resistance in A.gambiae and other vectors. New malaria control techniques are urgently needed in sub-Saharan Africa.

Now that the complete genomes of P. falciparum and A. gambiae have been sequenced researchers are confident that treatments ranging from vaccines to viruses that might specifically target the P. falciparum can be found. Other research has found that certain apical membrane antigens might be suitable for inclusion into a possible malaria vaccine.

Researchers are also interested in the sickle cell trait. Sickle hemoglobin provides the best example of a change in the hemoglobin molecule that impairs malaria growth and development. The initial hints of a relationship between the two came with the realization that the geographical distribution of the gene for hemoglobin S and the distribution of malaria in Africa virtually overlap. People (and particularly children) infected with P. falciparum are more likely to survive the acute illness if they have sickle cell trait.

References:

http://www.genomenewsnetwork.org/sequenced_genomes/genome_guide_p1.shtml
http://www.swissinfo.org/sen/swissinfo.html?siteSect=671&sid=1763610
http://pbl.cc.gatech.edu/mindy/1082
http://sickle.bwh.harvard.edu/malaria_sickle.html