Zika virus and conspiracy theories

When I first heard about the tragic cases of microcephaly in Brazil and how suspicion fell on the cause being the Zika virus, I facetiously remarked to a colleague that somehow someone would link it to GMOs. After all, Brazil is the world's second largest producer of genetically modified crops behind the United States with more than half of the agricultural acreage in Brazil devoted to growing such crops. Well, so far GMOs have not been implicated, but Monsanto has. That company of course has become a lightning rod for all sorts of crackpot theories, in this case one forged by a South American group calling itself "Physicians in Crop Sprayed Towns." This is an activist group opposed to the use of pesticides with the belief that these "poisons" are being foisted on the public by the World Health Organization and South American governments because they have been financially seduced by the evil chemical industry.

The alleged link to Monsanto is through pyriproxifen, a larvicide that is sprayed on wet areas where mosquities breed. This may well be the real link to the birth defects rather than the Zika virus according to Physicians in Crop Sprayed Towns. The fact is that Monsanto has absolutely nothing to do with producing or selling this chemical which is supplied by the Sumimoto Chemical Company. Sumimoto has partnered with Monsanto in the sale of herbicides but that has nothing to do with pyriproxifen, the chemical being targeted by this activist group. The Monsanto connection to pyriproxifen is non-existent, the name just being thrown in to get attention and stir the pot.

The supposed Monsanto connection is a non-issue in any case because the pyriproxifen link to microencephaly exists only in the minds of conspiracy theorists who claim that the cases of this type of birth deformity correlate with the introduction of pyriproxifen as a replacement for temephos, a larvicide to which mosquitoes have developed a resistance. The physicians who promote this notion must have skipped the class in medical school that discussed the difference between an association and a cause and effect relationship. They should be reminded that the use of facial tissue does not cause colds, even though colds and the use of such tissues are closely associated.

Of course associations can turn out to be cause and effect, but the one between microcephaly and pyriproxifen is almost certainly not one. The fact is that one would actually expect a correlation with larvicides if the disease is caused by a mosquito transmitted virus because it is exactly where mosquitoes thrive that larvicides are applied. Furthermore, there are areas where many cases of microencephaly have been noted where pyriproxifen has never been used. There is also extensive scientific literature on this chemical and no connection to any sort of birth defect has ever been noted.

Pyriproxifen has been widely used in tick and flea collars for pets for years without any problem. Finally, this particular larvicide's mode of action is interference with the functioning of a hormone that is found only in insects and there is no plausible mechanism by which it can interfere with mammalian physiology in a way that would cause microcephaly. What we have here is an activist group with a fixed agenda trying to fit whatever square peg they can find into a round hole they have drilled.

Dr. Joe Schwarcz
McGill Office for Science and Society