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Genetically Modifying Mosquitoes to ‘Bite the Dust’? Ethical Considerations

At some point, most people will have questioned the necessity of the existence of mosquitoes. In the UK at least, the things that might prompt us into such reflection are probably trivial; in my own case, the mild irritation of an itchy and unsightly swelling caused by a mosquito bite will normally lead me to rue the existence of these blood-sucking pests. Elsewhere though, mosquitoes lead to problems that are far from trivial; in Africa the Anopheles gambiae mosquito is the major vector of malaria, a disease that is estimated to kill more than 1 million people each year, most of whom are African children.

Although malaria is a curable disease if it is diagnosed and treated promptly (often through artemisinin-based combination therapy), this is not always possible. Furthermore, although prevention measures that are currently in place, such as spraying homes with insecticides, and installing mosquito nets, have led to some reduction in malaria fatalities, there is no denying that the disease still represents a huge health risk, particularly in Africa.

On Tuesday, it was reported that scientists have made a breakthrough in genetic modification that could be used in the fight against malaria. A team at Imperial College London have successfully genetically modified Anopheles gambiae mosquitoes so that the modified mosquitoes produce 95% male offspring. More importantly this reproductive tendency was inherited by the offspring of the modified mosquitoes.

As Andrea Crisanti, one of the authors of the study, told the Guardian newspaper, modifying the mosquitoes in this way has two benefits with regards to the prevention of malaria:


You have a short-term benefit because males don’t bite humans [and transmit malaria]. But in the long term you will eventually eradicate or substantially reduce mosquitoes. This could make a substantial contribution to eradicating malaria, combined with other tools such as insecticides.


There are a number of scientific challenges to using this sort of genetic modification technology to substantially reduce mosquito populations in the wild. Perhaps most saliently, in order for this approach to work, modified mosquitoes would have to mate with non-modified mosquitoes in the wild. Whilst this has happened in a lab environment, some scientists have suggested that is not yet clear whether modified mosquitoes would be able to successfully compete with non-modified mosquitoes for mates in the wild.

However, if this approach did have the effect of substantially reducing, or even eradicating populations of Anopheles gambiae, this would be of considerable moral significance. By eradicating the main vector of malaria, we would be saving hundred’s of thousands of lives; this would give us a strong moral reason to introduce genetically modified mosquitoes into the wild. However, there are two possible types of moral objection to this practice that I shall consider briefly here.

The first is consequentialist in nature; the consequentialist argument claims that whilst we might hope that eradicating Anopheles gambiae mosquitoes would have the good consequence of tackling the malaria problem, we cannot be certain that this will be the case, and it might also lead to some bad consequences.

There is perhaps some warrant to this objection. First, we cannot be certain that this approach will tackle the malaria problem. As I mentioned above, there is some doubt about whether modified mosquitoes would successfully compete with non-modified mosquitoes for mates in the wild; and this would be necessary for the mosquito population to be reduced. The authors of the study also concede that this gene would not spread indefinitely amongst the population even if it was transferred successfully to offspring. Furthermore, even if Anopheles gambiae were eradicated, a different species of mosquito would then become dominant, and we might worry that it could eventually mutate in such a way that members of the species would become prone to carrying the Plasmodium parasites that cause malaria. Second, it might be claimed that there could be some bad ecological consequences of eradicating mosquitoes in this way; for instance, mosquitoes represent an important food source for other animals (such as bats, fish and birds), and they are also pollinators of various plants.

However, whilst we should not dismiss this objection out of hand, it does not represent a compelling argument against genetically modifying mosquitoes. Whilst we cannot be certain that any experimental technique will have the results that we expect it will, there is perhaps some room for optimism in this particular context. As I mentioned above, modified mosquitoes have successfully mated in a laboratory setting, and, as the BBC reports, Crisanti’s team are developing a facility to test their hypothesis on a much larger scale. Furthermore, in other work, Crisanti and Windbichler have shown that it may be possible to implant a sex-distorter gene on the Y chromosome of a mosquito (rather than the X chromosome). If this became possible, then the gene would spread indefinitely through the population, since all the male offspring would inherit that particular gene (which is not so in the case of the X chromosome, where only half of the male offspring of the modified mosquito inherit the sex-distorting gene).

With regards to the possibility of a new dominant species of mosquito mutating in such a way that it becomes prone to carrying the Plasmodium parasites that cause malaria, this possibility cannot be completely ruled out. However, mutations do not happen overnight; even if another species were to mutate into a carrier in say ten years time, the eradication of Anopheles gambiae could still have led to approximately 10 million lives being saved over those ten years.

What about the potential bad ecological consequences?  Interestingly, in 2010, the journal Nature asked scientists who explore aspects of mosquito biology and ecology what would happen if mosquitoes were eradicated. The following quote from the entomologist Joe Conlon, of the American Mosquito Control Association in Jacksonville, Florida seems to represent the majority view of these experts:


[Mosquitoes] don’t occupy an unassailable niche in the environment. If we eradicated them tomorrow, the ecosystems where they are active will hiccup and then get on with life. Something better or worse would take over.


The second sort of objection to genetically modifying mosquitoes in this way is more deontological than consequentialist in flavour; the objection is that we ought not to interfere with nature in this way, since it amounts to ‘playing God’. This objection is familiar from the debate regarding genetically modified foods (it was voiced by HM Prince of Wales amongst many others).  The standard line of response for supporters of genetically modified foods to the ‘playing God objection’ has been to point out that humans have been selectively breeding both plants and animals for hundreds of years, and this amounts to an indirect form of genetic modification that we do not find morally problematic.

However, in the context that I am considering here, there is perhaps something more to the accusation of ‘playing God’; whilst we have modified organisms in a number of ways produce animals and plants that are better suited to providing us with food, we have not modified them with the express purpose of precipitating the extinction of a particular species.

Does this distinguish the proposed genetic modification of Anopheles gambiae from previous uses of genetic modification in a morally significant way? Certainly, it seems that that many would not believe it to be morally permissible to eradicate any animal in order to save the lives of some humans; for evidence of this, we need only look to the moral outcry against the recent shark cull in Western Australia. We can only imagine the degree of moral protest that would have occurred if scientists found a way to globally eradicate Great White Sharks through sex-distorting genetic modification!

However, there are a number of disanalogies between the mosquito case and this hypothetical eradication of Great White Sharks through genetic modification, two of which are pertinent here. First, Great White Sharks are responsible for a tiny proportion of deaths globally; from 1990-2011, Great White sharks were responsible for 29 deaths; millions of people died from malaria over that period. Second, mosquitoes are far less cognitively advanced than sharks; this presumably at least part of the reason why most people would think that there would be little wrong about killing an individual mosquito, but that there would be something wrong about killing an individual shark.

In fact, whilst it is true that we have not intentionally precipitated the extinction of a species through genetic modification, we have intentionally eradicated the Variola virus through vaccination programmes; and this was deemed, quite rightly, to be a cause for moral celebration, since the virus was responsible for smallpox, the most devastating disease in human history which claimed the lives of millions of people.  Given the limited sophistication of the Anopheles gambiae mosquito, and the number of lives at stake, there is, I believe, a good case for claiming that the proposed eradication of Anopheles gambiae has more in common with the eradication of smallpox than the hypothetical eradication of Great White Sharks.

The real moral challenge that this technology raises is the indirect effect that it might have on human population size if it works. Whilst we should celebrate the prospect of a technology that has the potential to save millions of lives per year, this will have its own effects. and it would be short-sighted in the extreme to actually embark on the project of attempting to eradicate malaria in this way, without giving some thought to the sorts of infrastructure that would need to be in place were we to be successful. So let us pursue the technology, and let us save these million of lives; but let us also address the question of how we must change the existing infrastructures so that we are able to accomodate the population increase that this technology might lead to. These questions of social justice represent the real moral challenge Iin this domain.


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