A team of German and American researchers have used enetic engineering techniques to develop mosquitoes with a severely impaired ability to transmit malaria--at least to mice, new study findings show. The research is a "first step in the right direction" towards combating malaria in humans, study author Dr. Marcelo Jacobs-Lorena, of Case Western Reserve University in Ohio. "We now know it is possible to genetically modify mosquitoes to block the development of the (malaria) parasite. If the parasite cannot develop, it's not transmitted," Jacobs-Lorena explained.
Malaria causes up to an estimated 1.5 million deaths per year. Vaccine development has so far proven unsuccessful since the malaria parasite lives in the bloodstream and therefore "evolves all the tricks to escape the body's immune defenses," Jacobs-Lorena said.
While pesticides have been used to kill the mosquitoes that carry malaria, the insects can develop resistance to pesticides. And the malaria parasites can become resistant to drugs used in humans, which requires the constant development of newer and consequently more expensive drugs.
As an alternative approach to combating malaria spread, Jacobs-Lorena and his colleagues attempted to genetically modify mosquitoes by introducing foreign genes into their germ line, or the genes that are passed on to future generations.
Once a mosquito consumes malaria-infected blood, the malaria parasite needs to cross over from the mosquito's gut into the blood in order to fully develop. In their research, published in the May 23rd issue of the journal Nature, Jacobs-Lorena and his team identified a snippet of protein called SM1 that attaches itself to the gut wall of the mosquito, essentially blocking the parasite.
The gene's activity is triggered when the mosquito feeds on blood, churning out SM1 "so when the parasite arrives, it doesn't find the right molecule," or any space to fit into, Jacobs-Lorena explained. The investigators found that the genetically modified mosquitoes were less susceptible to infection after feeding on a malaria-infected mouse and were far less able to transmit the malaria parasite to mice than normal mosquitoes. Two groups of mosquitoes they studied were unable to transmit the parasite and one group had a 50% reduction in transmission.
The research "promises to eventually have important applications," but further study is needed, Jacobs-Lorena said. For example, although the study results were positive when mice were used, it is not known whether SM1 will block transmission of the human malaria parasite.
Also, it is not clear if there is a safe and effective way to spread such genes into mosquitoes in general, and because the technique wasn't 100% effective at blocking transmission, the parasite could become "resistant" to the treatment.
Much work needs to be done to determine if such an approach could work, according to an editorial by Gareth Lycett and Fotis Kafatos, of the European Molecular Biology Laboratory in Heidelberg, Germany. Lycett and Kafatos note that the researchers studied a type of parasite that causes malaria in rodents. And little is known about how such "transformed" mosquitoes may affect the genes of mosquitoes in the wild.