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Zika Virus, Birth Defects, and Conspiracy Theories

Zika, a formerly unremarkable virus named for the forest in Uganda where it was discovered in 1947, is now the latest emergent disease to spawn serious concerns around the world. It is spread by a familiar mosquito, Aedes aegypti, and probably by the closely related Aedes albopictus, vectors notorious for spreading yellow fever, dengue, and chikungunya. Until recently, Zika had been reported at low frequency in various tropical locations, but since 2014, for reasons not fully understood, it has spread explosively throughout much of South America, especially Brasil. One key to its rapid spread has been the distribution of the mosquito vector, which has rebounded after robust and effective control measures were allowed to lapse throughout the Americas after their success in reducing the prevalence of yellow fever.

The mild fever that usually results from infection with the Zika virus is not the source of concern. The alarm associated with Zika follows the suspicion that infection during pregnancy causes mothers to deliver babies with microcephaly, a type of abnormal brain development marked by irreparable neurological defects with profound, lifelong implications. Even though the cause has not been determined conclusively, and there are questions about the epidemiological data from which correlation has been inferred, medical professionals are taking the threat seriously, and the Centers for Disease Control has advised pregnant women to avoid travel to Zika-infested regions.

Fringe elements have been quick to offer conspiracy theories in various flavors to explain these alarming new developments. The starting point in this case seems to be a January 25 Reddit post from the Conspiracy subreddit, which argued the cause of the outbreak was a field trial of a genetically modified (GM) mosquito intended to reduce populations of Aedes aegypti to help control chikujngunya and yellow fevers, developed by a British company, Oxitec. This myth was quickly taken up by an environmental journal that some, at least, had once considered somewhat credible, which wasted little time pushing the claim. This unsupported speculation was quickly debunked by skeptics who actually consulted the evidence and noted multiple fatal flaws to the conspiracy theory:

  • The (first) GM mosquito field trial took place nearly 400 miles from the center of the Zika outbreak, and three years prior;
  • The second was nearly 1,200 miles away;
  • Neither outbreak is consistent with the timing or distribution of reported cases in the outbreak; and
  • The pest-controlling GM mosquitoes introduced in the field trials (where they successfully suppressed the target pests by more than 90 percent) were only males, which do not bite, and therefore could not spread disease even if they themselves were infected, which they were not.

There are numerous further fatal flaws in this crackpot theory, exhaustively and deliciously eviscerated by Christie Wilcox in the blogpost cited, which is itself a thing of beauty that all are urged to read. Nevertheless, a new zombie myth has been added to the cannon and can be counted on to circulate for years, and it has already had disastrous consequences. And the GM mosquitos have been so effective that the World Health Organization (WHO) strongly urges their use be increased as rapidly as possible. But wait – there’s more!

Not to be outdone by the GM conspiracy theorists, campaigners opposed to “chemicals” have their own take on the situation. And consistent with substantial overlap between the two populations, they find a different, but familiar villain in, wait for it… Monsanto!

In this case, we have claims originating with a group in Argentina calling themselves the “Physicians in the Crop-Sprayed Villages” insisting that the true cause of the microcephaly reported in north eastern Brasil is not the Zika virus, but rather a pesticide known as pyriproxyfen which is used to control the mosquito vector, “manufactured by Sumimoto [sic] Chemical, a Japanese subsidiary of Monsanto.”

Individuals pushing this speculation have a history of making unsupportable claims grounded in dubious methodology, and they have attracted the support of a cadre known for extremist views uninhibited by respect for data. Fifteen seconds on the Internet is sufficient to clarify that Sumitomo, one of the crown jewels of Japanese industry with roots 400 years deep, is nobody’s subsidiary. And although Sumitomo does manufacture pyriproxyfen, a further thirty seconds on the Web would suffice to falsify the allegation that pyriproxyfen has anything to do with microcephaly, in Argentina, Brasil, or any place else. Monsanto has repudiated the claims, which, of course, to the conspiracists, is as good as an admission of guilt. So consider the views of some independent third parties. Ian Musgrave is a Senior Lecturer in the Faculty of Medicine at the University of Adelaide. He has summarized the essential facts:

This claim is not plausible. The pesticide in question is pyriproxyfen, a replacement for the organophosphate pesticides that the mosquitoes are becoming resistant to. Pyriproxyfen acts by interfering with the hormonal control growth cycle of insects from hatching, to larvae, to pupa. This hormone control system does not exist in organisms with backbones, such as humans, and pyriproxyfen has very low toxicity in mammals as a result… a person would have to drink well over 1,000 litres of [treated] water a day, every day, to achieve the threshold toxicity levels seen in animals. The effect of pyriproxyfen on reproduction and fetal abnormalities is well studied in animals. In a variety of animal species even enormous quantities of pyriproxyfen do not cause the defects seen during the recent Zika outbreak.

This should be the end of the story, except that, of course, it isn’t. This new iteration of the zombie myth is now ricocheting through the echo chamber where, together with the retracted and discredited claims from Séralini and Pusztai, it will no doubt remain undead. But Adjunct Professor Andrew Batholomaeus from the University of Canberra and the School of Medicine, University of Queensland, has noted,

…the use of pyriproxifen is driven by WHO recommendations and not the marketing activity of any multinational or other corporation. The potential human health consequences of discouraging the use of pyriproxyfen in drinking water storage and other mosquito-reduction programs is catastrophic with potential deaths and serious disease from otherwise avoidable malaria, dengue and other mosquito-borne diseases numbered in at least the hundreds of thousands. If these reports and suggestions are motivated by anything other than ignorance and poor scholarship they are deserving of the most strident condemnation. Journalists covering this story would do well to research the background of those making and reporting the claims as the underlying story and potential public health consequences may be far more newsworthy than the current headlines”

In this case, as in so many others, the truth turns out to be the opposite of what is claimed by the conspiracists. Far from causing the Zika outbreak, Oxitec is offering the only viable solution to the problem short of a vaccine that would likely take at least a decade to deliver. But Oxitec has a proven method for suppressing the disease vector that is available right now, today, and which those in the areas worst afflicted are rushing to implement. We need to remember that data and experience remain a superior basis for decision-making than myths. Policymakers, please take note.

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