Using mutant mosquitoes to kill malaria can be dangerous for humans
While eliminating disease one needs to be doubly aware of the consequences that nature may seek to impose its own compensation.
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Sickle-cell anaemia is an inherent genetic disorder prevalent mostly among the Sub-Saharan population. It is caused by an abnormality in the oxygen-carrying protein in blood - S. Haemoglobin. Due to a malformed genetic codes, the haemoglobin present in people suffering from this disorder is defective.
As a result, the protein undergoes structural changes and the Red blood cells (RBCs) look sickle-shaped. This further exposes those that are affected by the disorder to a high risk of cardiovascular and vaso-occlusive diseases. And, in turn, leads to high child mortality rate within the Sub-Saharan population.
A strange, but important part of this disease, is that this genetically varied population affected by sickle cell anaemia is resistant to malaria. Given the fact that nearly two million people die of malaria annually, and ninety per cent are from the Sub-Saharan belt, scientists and microbiologists have been trying for decades to figure out the root of this resistance.
Some of them are of the view that the disease is a classic example of Darwin’s theory of natural selection and the theory of adaptability of organisms to their environment. It is a way by which nature helps in developing immunity against whatever is destructive in the immediate environment, but in the process, also forces the body to biologically compensate otherwise.
In this case, sickle-cells that may be resistant to malaria, but are malformed and are at a higher risk of developing other blood-related disorders. In the grand scheme of things it can be said that nature has its own way of imposing compensation.
Last month when scientists at the University of California successfully engineered a breed of Anopheles mosquito (Anopheles stephani) that’s supposed to be genetically resistant to malaria, they perhaps had no idea that in a few weeks' time, people at the Imperial College London (ICL) would come up with another breed that wouldn’t even need to resist.
This new breed of genetically modified mosquito called Anopheles gambiae is engineered to be infertile and pass down the trait rapidly. Through a technology called Gene Drive, scientists at the Imperial College are working at accelerating the process of passing down of the gene to the offsprings so that the breed of female Anopheles, the carrier for the malaria parasite, is wiped out soon.
Molecular biologists Tony Nolan and Andrea Crisanti at the ICL have identified three genes that code for fertility in the Anopheles species. These genes could be targeted to be modified and introduce infertile variants into the population.
They have also claimed that they are looking for other genes that could code for fertility and in the process they would aim to modify every gene that is responsible for passing down of the trait. While the process may take a long time, it is expected that the breed of Anopheles mosquito can be successfully eliminated from the environment in the next ten years.
So, like smallpox and polio, malaria too can be expected to be eradicated in a decade or so.
While there are 3,400 species of mosquitos worldwide, Anopheles is only one among the 800 species of mosquitos found in Africa. So eliminating them from the food chain will not significantly affect the eco system, says Tony Nolan.
But as Professor Austin Burt from the Department of Life Sciences at ICL says, it will take a long series of trials and control experiments to figure out a successful elimination plan. It might even be a concern, adds Kevin Esvelt from Harvard, that the mosquito as well as the parasite may develop resistance against the modification and the process employed for elimination.
Though in this process, artificial selection is given privilege over Darwin's theory of natural selection, it's been observed, as in the case of sickle-cell anaemia that nature schemes out its own evolutionary processes to compensate the lack created in the ecosystem.
Though Anopheles contributes to a small percentage of the population of mosquitos worldwide, it still is a significant entity in the food chain. Elimination of anything from the food chain will create a lack, however minute, and most of the times an ecological lack leads to mutative traits in the organism targeted or in other related species of the same.
This further could lead a pathogenically evolved mosquito and may put some other population at a higher risk. It could be drawn as a caveat that micro-organisms have a high mutation rate when it comes to their virulence. Therefore, it can be expected that while the process of elimination may take a decade or so, during this time another strain of the malaria parasite may make its appearance in the scene.
Therefore, scientists aiming at the eradication of malaria, not only have to check the control trials at genetically modifying the Anopheles gambiae, but also have to ensure that the parasite, Plasmodium, does not find expression in other organisms as mutated strains.
We do not know how far artificial selection will take us, but while expecting for the elimination of the disease one needs to be doubly aware of the consequences that nature may seek to impose compensation on the human population.