One of the defining characteristics of conspiracy theorists is how they will switch rapidly between seemingly competing implausible theories to explain unconnected events in any way that confirms their biases. So it is with the anti-GMO lobby, which seems to be behind the latest attempt to exonerate Aedes aegypti mosquitoes for any role in causing Zika or the related outbreak of microcephaly in Brazil and neighbour countries.
A fortnight ago it was GM mosquitoes released by Oxitec which were supposedly behind Zika. This utterly implausible theory appealed to the anti-GMO crowd because it enabled them to scaremonger about genetic engineering while at the same time demonising a potential solution to mosquito control that involved a novel use of genetics in insects and was therefore bad. Along with many others in the pro-science community, I debunked this theory in the Guardian, and it quickly died away.
A couple of weeks later, the old theory is forgotten, and a new one is doing the rounds – and being shamefully promoted, again, by the once-great Ecologist. Again the Zika virus, and, contrary to prevailing medical expert opinion, the mosquitoes are innocent of causing microcephaly. This time the culprit is pyriproxyfen – a larvicide that is added to municipal water supplies in Latin America in order to prevent mosquitoes breeding.
It is interesting that what the two theories have in common is an attempt to blame one of the solutions to Zika and microcephaly for causing it in the first place. This theory has appealed to the anti-GMO crowd because at last – at last! – they have been able to get the name ‘Monsanto’ into the picture: a necessary bit of clickbait necessary to give the new theory viral traction on social media.
The origination of the story is an Argentine group called ‘Physicians in the Crop-Sprayed Villages’ – an anti-GMO outfit that campaigns against the use of glyphosate in Argentinian large-scale soya farming. In the past it has made numerous scientifically unsupported claims about glyposate being responsible for cancer and birth defects. In its Zika press release, the group claimed that the larvicide “pyroproxyfen” (spelt wrong, incidentally) “is manufactured by Sumimoto Chemical, a Japanese subsidiary of Monsanto”.
Scary! Everyone knows Monsanto is evil – so blaming them and some Japanese ‘chemical’ company is a great way to confirm biases for anti-GMO types and chemophobes in general. Except that it’s completely wrong. For a start the company is called Sumitomo, not Sumimoto. More importantly, as a Monsanto spokesperson told me: “Sumitomo is not owned by Monsanto. However, we do have a long-standing business relationship – they supply us with a couple of herbicides.” Guilty! Hang them!
The science as usual, is somewhat different. As Dr Ian Musgrave at the University of Adelaide explains:
“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.”
In order to achieve threshold toxicity levels that have been seen in animal studies, a person would have to drink 1,000 litres of water every day. The concentration of pyriproxyfen in Brazilian treated water is 300 times lower than the safe limit set by the World Health Organisation. (h/t Science Media Centre for this and other expert quotes.) And so on.
The toxicity of pyriproxyfen is well understood, and the WHO does not consider it carcinogenic, genotoxic or teratogenic at anything less than extreme doses. There isn’t even much correlation between treated areas and microcephaly cases – not least because, as Sumitomo has pointed out in a media response, its larvicide has been used in dozens of countries around the world for two decades already.
The problem with conspiracy theories isn’t just that they waste everyone’s time and confuse people, but that they are actively harmful. Already, according to the WSJ, one Brazilian state, Rio Grande do Sul, has banned the use of pyriproxifen in drinking water “as a preventive measure”. An increase in both Zika and Dengue fever cases can reasonably be expected as a result: many people will suffer and some will die because this new conspiracy theory is polluting the public discourse. But the science deniers get their ideological biases confirmed, which to them is much more important.
As I said in the Guardian, we have seen this before, and we know where it leads.