Saturday, January 9, 2010

Malaria Marches On

Malaria has been eliminated from a large part of the world. Other parts of the world have not been so fortunate.

In sub-Saharan Africa, it is now estimated that there are more than 360 million clinical cases and one million deaths due to malaria each year. Despite ambitious goals such as those of the Roll Back Malaria Initiative to halve malaria deaths by 2010, mortality from the disease has actually risen halfway through the program.

The failure of existing methods for malaria control has sparked interest in several new approaches.

It has been shown that most species of mosquitoes do not transmit malaria, and even among species that do, many individuals seem incapable of transmitting the disease, i.e., are refractory. Hence the genes that permit malarial infections in mosquitoes can be identified and then replaced or altered in terms of their function.

The laboratory of Marcelo Jacobs-Lorena at Johns Hopkins University has successfully identified receptor sites for proteins that the parasite requires to pass through the gut after ingestion. The lab has produced small proteins that saturate the receptor sites and hence block amplification and transmission of the parasite.

These genetically modified mosquitoes (GMMs) can be deployed to either reduce population sizes or to replace existing populations with vectors unable to transmit the disease.

Other methods for generating refractoriness involve using antibodies that kill parasites within the mosquito and discovering genes that govern refractoriness in natural populations. A great deal is being discovered about the immune system of mosquitoes, leading many researchers in this field to believe that an effective gene construct to reduce the ability of mosquitoes to transmit malaria is not far away.

It is interesting that while a variety of means were used to eradicate malaria in North America and Europe, the most important are thought to be reducing the number of breeding sites for malaria vectors and improving residential areas to separate humans from mosquitoes.

Article published in PLoS MEDICINE February 2010
doi:10.1371/journal.pmed.1000020

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