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article imageWhy do some mosquitoes carry malaria?

By Tim Sandle     Dec 3, 2014 in Science
Researchers have genetically mapped 16 Anopheles mosquito species. Anopheles mosquitoes transmit human malaria parasites. Scientists are curious to understand why only a few dozen of the 500 different Anopheles species worldwide transmit malaria.
Scientists have been examining why there are genetic differences between those species of mosquito that can transmit parasites and the vast majority of mosquitoes that are, essentially, harmless.
Malaria is caused by a single-celled parasite belonging to genus Plasmodium. The parasite is transmitted by mosquitoes in over 100 countries. The disease presents a risk to around 3.3 billion people. Certain species of mosquito spread the parasite to humans through their bites; the parasite then travels to the liver, where it matures and reproduces in forms that infect the red cells and cause clinical symptoms. Worryingly, drug-resistant varieties of the disease have been rising for several years and the disease is becoming harder to control.
While around about half the world's population are at risk of malaria, most fatalities occur in sub-Saharan Africa. In this region the major vector species Anopheles gambiae dominates. Scientists are keen to understand why this particular mosquito became highly specialized in order to feed upon humans.
To study this further, DNA sequencing was undertaken. Scientists looked at reproductive processes, immune responses, insecticide resistance, and chemosensory mechanisms. Here, A. gambiae was compared with less harmful species and the results analysed through powerful computers.
It was found that with A. gambiae, some genes, particulalry those involved in reproduction or those that encode proteins secreted into the mosquito saliva, where quite different.
For the next stage of the research, scientists want to understand why some mosquitoes breed in salty water while others need pools of fresh water, or why some species are attracted to livestock while others will only feed on humans.
The research has been published in the journal Science. The research is titled “Highly evolvable malaria vectors: The genomes of 16 Anopheles mosquitoes.”
In related news, scientists have identified a several compounds that may lead to different ways to fight the malaria. Specifically, a university team has identified 31 enzyme-blocking molecules that could halt malaria before symptoms start.
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