The Larvicide Affair: The Ripple Effects of Zika Misinformation in Brazil

In my previous post about Zika, I mentioned a lingering question of whether the virus or a larvicide was the cause for microcephaly birth defects.

At the 2016 AAAS meeting I discussed in that post, I was asked about a public statement released by an environmentalist group from Argentina called Reduas. The statement linked the rise in microcephaly seen in Brazilian newborns to the larvicide pyriproxyfen. Reduas also accused the Brazilian Ministry of Health of falsely linking microcephaly to the Zika virus as an excuse to mass-spray the country with a teratogenic larvicide. Reduas claimed that the area where microcephaly is present in high numbers overlaps with the area where the larvicide was sprayed.

To bolster their claims, they refer to a previously published text from a Brazilian medical group called Abrasco, which addressed the inadequacy of Aedes aegypti extermination policies in Brazil. However, Abrasco’s purpose in this report was to encourage improvements in Brazilian sanitation infrastructure as a better approach than the use of insecticides. That’s nowhere near stating that the larvicide is a cause of a specific issue, much less of microcephaly.  It appears that Reduas misconstrued the Abrasco text to match their claim. The Brazilian doctors from Abrasco quickly went to the media to emphasize that their original statements are unrelated to Reduas insecticide claims.

Additionally, the sweeping claim from Reduas ignored the fact that several  areas affected with microcephaly in Brazil were not sprayed with pyriproxyfen.  The State of Pernambuco, with the highest number of cases of microcephalic babies, clarified that they had always used an environmentally-friendlier larvicide called BTI, and not pyriproxyfen — as claimed by Reduas. Still, soon after the release of the Reduas statement, a southern Brazilian state made the decision to stop spraying pyriproxifen.

The Reduas claim ignores substantial scientific and medical advice that supports the current thinking of researchers around the world that the Zika virus is the most likely link to microcephaly (and not the pesticide). 

I wish to call attention to two other misleading statements made by Reduas in their public communications regarding pyriproxyfen:

  1. They state that this insecticide (which is recommended by WHO for poor countries in their Guidelines for Drinking Water Quality) is having teratogenic effects, but they do not mention that this teratogenic effect occurs only in insect larvae.
  2. They infer that since humans share 60% of their genetic material with insects, the impact of exposure to pyriproxyfen on people will be same as on the teratogenicaly-mutated insect larvae.

Last December, the Brazilian Ministry of Health and WHO officially accepted the Zika-microcephaly link as probable enough cause to support measures to fight the disease (one of which is the use of pesticides to attack the carrier mosquito). The government then purchased several tons of the larvicide pyriproxyfen and donated it to local state governments.

Pernambuco created a working group to decide on the use of the larvicide pyriproxyfen; a group which eventually opted to not use the free larvicide. Thus, in the area most affected by microcephaly, a local government was still making critical decisions based on the false claims put out by Reduas.

These Reduas claims have created a dangerous climate of fear of pesticides in a country where mosquitoes are the carriers of several life threatening-diseases, including: Dengue, Yellow Fever, Chikungunya, and Zika viruses.

A cascade of misinformation can lead to decisions that can have serious consequences: people could disregard warnings to avoid travel to endemic areas and they could stop the use of bug repellents and long sleeves.  Governments could decide to stop the use of pesticides to exterminate the mosquito carrier of a dangerous virus — as already happened in Pernambuco.

Featured image: a Brazilian worker sprays neighborhoods for preventing infectious diseases such as the ones caused by mosquito Aedes aegypti. Photo by Prefeitura de Votuporanga – Flickr, CC BY 2.0.

Author: Mike Klymkowsky

A professor of Molecular, Cellular, and Developmental Biology at the University of Colorado Boulder ( I have long standing research interests in phage biology, molecular structure, cytoskeletal and regulatory (signaling) systems, and the improvement of science (biology and chemistry) courses, curricula, and outcomes (see

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