Transgenic mosquitoes could fight malaria

By: Tiffany Ng

Posted: 5/1/08

Approximately 500 million people contract malaria each year, and another one million die from the disease. Malaria is caused by a parasite that is transmitted by mosquitoes; humans contract the disease primarily from mosquito bites.

Though there are drugs that combat the disease, they do little to stop the actual spread of the disease. Furthermore, many parasites have developed resistance to the more commonly used and readily available drugs, such as chloroquinine, requiring the use of more expensive and dangerous drugs.

Insecticide-treated mosquito nets have been effective in preventing malaria transmission, but after decades of use, insecticides have begun to lose their efficacy against mosquitoes that have developed a resistance.

Therefore, it is clear that new methods for preventing the spread of malaria are necessary. Scientists have gone straight to the source of the disease and have identified mosquitoes with natural resistance to the parasite. They have subsequently been able to introduce the genes that confer this resistance into the genomes of mosquitoes that normally do not exhibit this trait.

With these genetically modified "transgenic" mosquitoes, the ultimate goal would be to introduce them into wild mosquito populations, which would spread the malaria-resistant genes throughout the population. However, these transgenic mosquitoes may be unable to survive as well as the wild populations.

At the Bloomberg School of Public Health, researchers tested the fitness of these transgenic mosquitoes compared to wild-type mosquitoes. Three populations of transgenic mosquitoes were observed, and compared with unmodified mosquitoes, they typically exhibited longer larvae development times, lower male mating rates and reduced net reproductive rates.

When transgenic and wild-type mosquitoes were raised together in cage experiments, two of the populations remained stable, but one decreased gradually. This decrease is due to the fact that the transgenic mosquitoes reach sexual maturity later than the wild mosquitoes, allowing the wild populations to get a head start on mating and reproduction.

Though these experiments demonstrate the need to produce multiple lines of transgenic mosquitoes to determine the one with the greatest fitness, it also has several important ramifications for the eventual introduction of transgenic mosquitoes into the wild. Since these mosquitoes generally do not survive as well in the wild, the methods to introduce them into the wild must give them a significant advantage over the natural populations.

Additionally, there are several ethical, legal and social issues that surround the potential introduction of transgenic mosquitoes into the wild. Not only are there concerns over the environmental impact of releasing genetically modified organisms, there is also the matters of consent and consensus of the communities into which the mosquitoes would be released.

Nevertheless, this research has the potential to significantly reduce the incidence of malaria in countries where the incidence of the disease is high and preventative measures are low. By targeting the sole transmitter of the malaria parasite to humans, the disease can be stopped before it even affects the lives of those living under malaria's threat.