Genetic Technique to Combat Malaria

With human death tolls reaching over 600,000 people a year from malaria-carrying mosquitos, researchers are reinventing the weaponry that scientists and health experts use to fight malaria. The current methods that range from spraying insecticides, to distributing millions of bed nets, and even draining entire swamps.  These methods have proved to be extremely limited in their effectiveness, allowing malaria to remain one of mankind’s most lethal killers.

New methods scientists have developed actually target and alter the DNA of the mosquitos. The proposed mechanism is a system of molecules that allows scientists to target and alter DNA with exquisite precision. The system, called Crispr, specifically designs molecules that attach to DNA in a specific location. This allows researchers to slice out the DNA at these locations — a small portion or an entire gene — and then use a prompt cell to replace it with a new segment or gene designed by the scientists.

The entire process would start in a lab with scientists inserting a “package” of genes into a group of mosquitos. Part of the “package” will include a gene that codes for a protein which makes the mosquitoes resistant to malaria parasites. By releasing these genetically engineered mosquitoes into the wild, allowing them to mate with their normal counterparts. The Crispr molecules are designed to target the other parent’s genetic material passed to the offspring, which would altered with the new resistance gene.

The newly bred offspring will now carry two copies of the resistance gene instead of just one like their parents. In theory, by harnessing genetic material and utilizing the natural reproductive capabilities of mosquitoes, it could take just a few years before every mosquito is resistant to malaria.

Obviously this system is in the very preliminary stages of being applicable in the real world. There are many concerns and questions about Crispr that have yet to be addressed.  One thing that concerns me is how this could possibly not work in the long run. A study published recently by Smallegange and colleagues in PLoS ONE examines the relationship that seems to exist between the malaria parasite and it’s host. Many people believe the two are engaged in a commensalistic relationship, regarding the parasite as the beneficiary and the mosquito as the neutral host (neither benefiting nor harmed). New evidence suggests that the relationship is actually more symbiotic than it is given credit for. There is a statistically significant association (P=0.0017) regarding the landing rate of mosquitoes infected with P. falciparum in the presence of human odor than those uninfected (Smallegange et al. 2013). This research could suggest that once infected with the malaria parasite, mosquito behavior can be dramatically altered. Infected mosquitoes may have an increased ability to either detect the presence of humans, or more likely an enhanced drive to try to feed on human blood. Bottomline, the presence of malaria enhances their attraction to humans.

I fear that if this mutualistic relationship has developed an evolutionary purpose for the survival of mosquitoes, the introduction of the Crispr system could be short lived. Evolution is smarter than humans. Given the vast number of wild mosquitoes and extremely short breeding time, it’s not impossible that mosquitoes could develop a specific preference for mosquitoes infected with malaria, since it could give them a selective advantage. Hopefully we have learned from our mistakes of the past, and will consider every possible consequence before implementing such a radical change into the global ecosystem.

 

Smallegange, R. C., G.-J. van Gemert, M. van de Vegte-Bolmer, S. Gezan, W. Takken, R. W. Sauerwein, and J. G. Logan. 2013. Malariai infected mosquitoes express enhanced attraction to human odor. PLoS ONE 8:e63602 EP

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