Zika Virus and a hypothesis regarding the impact of Pyriproxyfen

15 Feb

I have been interested in the Zika Virus ever since I heard about it while visiting Brazil last year to give a talk at the Brazilian Natural Products conference. What I did not expect was the incredible surge in worldwide attention that Zika would attract. I am grateful to have been included in the work led by Sean Ekins (@collabchem) in the perspective “Open Drug Discovery for the Zika Virus” recently published on F1000Research. Up until last week the hypothesis was that Zika was a mosquito-borne disease but now the suggestion is that the disease may be related to a larvicide.

The chemical in question that is being named as the offending agent is Pyriproxyfen. I had never even heard of this chemical until a couple of days ago. At that time there was nothing on Wikipedia but, of course, it has since been updated with this

“In 2014, pyriproxifen was put into Brazilian water supplies to fight the proliferation of mosquito larvae.[2] Some Brazilian doctors have hypothesized that pyriproxyfen, not the Zika virus, is the cause of the 2015-2016 microcephaly epidemic in Brazil. [3]

Consequently, in 2016, the Brazilian state of Rio Grande do Sul suspended pyriproxyfen’s use. The Health Minister of Brazil, Marcelo Castro, criticized this step, noting that the claim is “a rumor lacking logic and sense. It has no basis.” They also noted that the insecticide is approved by the National Sanitary Monitoring Agency and “all regulatory agencies in the whole world”. The manufacturer of the insecticide, Sumitomo Chemical, stated “”there is no scientific basis for such a claim” and also referred to the approval of pyriproxyfen by the World Health Organization since 2004 and the United States Environmental Protection Agency since 2001.[4]

Noted skeptic David Gorski discussed the claim and pointed out that anti-vaccine proponents had also claimed that the Tdap vaccine was the cause of the microcephaly epidemic, due to its introduction in 2014, along with adding “One can’t help but wonder what else the Brazilian Ministry of Health did in 2014 that cranks can blame microcephaly on.” Gorski also pointed out the extensive physiochemical understanding of pyriproxyfen that the WHO has, which concluded in a past evaluation that the insecticide is not genotoxic, and that the doctor organization making the claim has been advocating against all pesticides since 2010, complicating their reliability.[2][5]

Because we live in a time of Open Data, and at a time when there is soooooo much information available on open databases, I thought I would go after any evidence-based identification of the chemical as a potential contributor to the explosion in Microcephaly.

PubChem exposes a LOT of useful data under the Safety and Hazards tab. The long-term exposure points to issues with blood and liver. FIFRA requirements are listed on PubChem and toxicity data is also available here. Reproductive toxicity is limited to reports in animals that reports

/LABORATORY ANIMALS: Developmental or Reproductive Toxicity/ In /a/ developmental study in rats, a maternal NOAEL/LOAEL were determined to be 100 mg/kg/day and 300 mg/kg/day, respectively. These findings were based on increased incidences in mortality and clinical signs at 1,000 mg/kg/day with decreased in food consumption, body weight, and body weight gain together with increases in water consumption at 300 and 1,000 mg/kg/day. The developmental NOAEL /and/ /LOAEL were 100 mg/kg/day and 300 mg/kg/day /respectively/ based on the incr of skeletal variations at 300 mg/kg/day and above.

64 FR 56681 (10/21/99). Available from, as of April 28, 2003:
/LABORATORY ANIMALS: Developmental or Reproductive Toxicity/ In /a/ developmental study in rabbits, the maternal NOAEL/LOAEL for maternal toxicity were 100 and 300 mg/kg/day based on premature delivery/abortions, soft stools, emaciation, decreased activity and bradypnea. The developmental NOAEL was determined to be 300 mg/kg/day and developmental LOAEL was /not/ … determined; no dose related anomalies occurred in the four remaining litters studied at 1,000 mg/kg/day.

64 FR 56681 (10/21/99). Available from, as of April 28, 2003:
/LABORATORY ANIMALS: Developmental or Reproductive Toxicity/ In a 2-generation reproduction study in rats, the systemic NOAEL was 1,000 ppm (87 mg/kg/day). The LOAEL for systemic toxicity was 5,000 ppm (453 mg/kg/day). Effects were based on decreased body weight, weight gain and food consumption in both sexes and both generations, and increased liver weights in both sexes associated with liver and kidney histopathology in males. The reproductive NOAEL was 5,000 ppm. A reproductive LOAEL was not established.

64 FR 56681 (10/21/99). Available from, as of April 28, 2003:
Just to point out that this information, and it is valuable, is sourced from HSDB.
Pyriproxyfen reports on PubMed doesn’t seem to turn up anything about birth defects that I can find.
There is no evidence, yet, for the potential impact of this chemical on the incidence of microcephaly but the hypothesis is now out there and it will be interesting to see what happens as investigations are pursued. As yet I have no opinion….but will be watching with interest to see what comes out.

About tony

Antony (Tony) J. Williams received his BSc in 1985 from the University of Liverpool (UK) and PhD in 1988 from the University of London (UK). His PhD research interests were in studying the effects of high pressure on molecular motions within lubricant related systems using Nuclear Magnetic Resonance. He moved to Ottawa, Canada to work for the National Research Council performing fundamental research on the electron paramagnetic resonance of radicals trapped in single crystals. Following his postdoctoral position he became the NMR Facility Manager for Ottawa University. Tony joined the Eastman Kodak Company in Rochester, New York as their NMR Technology Leader. He led the laboratory to develop quality control across multiple spectroscopy labs and helped establish walk-up laboratories providing NMR, LC-MS and other forms of spectroscopy to hundreds of chemists across multiple sites. This included the delivery of spectroscopic data to the desktop, automated processing and his initial interests in computer-assisted structure elucidation (CASE) systems. He also worked with a team to develop the worlds’ first web-based LIMS system, WIMS, capable of allowing chemical structure searching and spectral display. With his developing cheminformatic skills and passion for data management he left corporate America to join a small start-up company working out of Toronto, Canada. He joined ACD/Labs as their NMR Product Manager and various roles, including Chief Science Officer, during his 10 years with the company. His responsibilities included managing over 50 products at one time prior to developing a product management team, managing sales, marketing, technical support and technical services. ACD/Labs was one of Canada’s Fast 50 Tech Companies, and Forbes Fast 500 companies in 2001. His primary passions during his tenure with ACD/Labs was the continued adoption of web-based technologies and developing automated structure verification and elucidation platforms. While at ACD/Labs he suggested the possibility of developing a public resource for chemists attempting to integrate internet available chemical data. He finally pursued this vision with some close friends as a hobby project in the evenings and the result was the ChemSpider database ( Even while running out of a basement on hand built servers the website developed a large community following that eventually culminated in the acquisition of the website by the Royal Society of Chemistry (RSC) based in Cambridge, United Kingdom. Tony joined the organization, together with some of the other ChemSpider team, and became their Vice President of Strategic Development. At RSC he continued to develop cheminformatics tools, specifically ChemSpider, and was the technical lead for the chemistry aspects of the Open PHACTS project (, a project focused on the delivery of open data, open source and open systems to support the pharmaceutical sciences. He was also the technical lead for the UK National Chemical Database Service ( and the RSC lead for the PharmaSea project ( attempting to identify novel natural products from the ocean. He left RSC in 2015 to become a Computational Chemist in the National Center of Computational Toxicology at the Environmental Protection Agency where he is bringing his skills to bear working with a team on the delivery of a new software architecture for the management and delivery of data, algorithms and visualization tools. The “Chemistry Dashboard” was released on April 1st, no fooling, at, and provides access to over 700,000 chemicals, experimental and predicted properties and a developing link network to support the environmental sciences. Tony remains passionate about computer-assisted structure elucidation and verification approaches and continues to publish in this area. He is also passionate about teaching scientists to benefit from the developing array of social networking tools for scientists and is known as the ChemConnector on the networks. Over the years he has had adjunct roles at a number of institutions and presently enjoys working with scientists at both UNC Chapel Hill and NC State University. He is widely published with over 200 papers and book chapters and was the recipient of the Jim Gray Award for eScience in 2012. In 2016 he was awarded the North Carolina ACS Distinguished Speaker Award.

Posted by on February 15, 2016 in Uncategorized


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