28
Sep
Common Mosquito Pesticide Exacerbates Health Issues Associated with Zika Virus
(Beyond Pesticides, September 28, 2021) A widely used mosquito pesticide may exacerbate the effect of the Zika virus on fetal brain development, according to research published by an international team of scientists in the journal Environmental Pollution. Pyriproxyfen, an insect growth regulator often used as a mosquito larvicide, is registered for use in hundreds of commonly used pesticide products. But scientists have discovered that the pesticide’s mode of action has the potential to worsen the public health mosquito diseases the chemical aims to control. The research reinforces the extent of unknowns associated with synthetic pesticide exposure, underlining the need for a focus on nontoxic and ecological mosquito management.
Scientists base their research on reports that in Brazil, during the 2015 Zika epidemic, certain areas of the country experienced higher rates of microcephaly. Microcephaly is a rare condition that causes pregnant women’s fetus to develop severe cranial deformities, alongside a range of other symptoms that include vision problems, hearing loss, feeding issues, developmental delays and seizures. The present study aimed to see how pyriproxyfen, used at higher rates in areas where microcephaly Zika cases were recorded, may interact with the virus.
In an article published in The Conversation, researchers note that until now data on the role of pyriproxyfen in the microcephaly epidemic showed contradictory results. Based on prior research, it was hypothesized that a particular metabolite of pyriproxyfen (4′–OH–PPF), rapidly metabolized in the body of both people and wildlife (vertebrates and invertebrates), was playing a role due to its effects on thyroid hormone production. As the study notes, “[thyroid hormones] THs are key to evolutionary expansion of brain size and complexity, a primary characteristic of humans.”
To test this hypothesis, researchers used genetically engineered tadpoles developed to light up green in the presence of thyroid hormone. Once these tadpoles were dosed with the chemical, their green coloring diminished significantly, indicating that pyriproxyfen was blocking the production of thyroid hormones.
Effects on the thyroid were targeted for analysis because of the critical role thyroid hormones play in the development of brain cells. In a follow up experiment, scientists took stem cells created from mouse brains and exposed them to varying levels of the pyriproxyfen metabolite. As dosage increased, so did the death of brain cells.
Researchers discovered that tadpole brains exposed to the chemical display altered gene expression. Focus increases on one particular gene – Msi1, which contains the protein Musaschi-1. Zika employs that protein in order to transmit the virus to other cells in an individual’s body. In the mouse experiment, brain cells that did not die after chemical exposure were found to contain higher levels of this protein.
“That’s why we hypothesized that, through increasing Musaschi-1, pyriproxyfen could allow the virus to replicate faster,” the authors wrote in The Conversation. While the study does not provide support for the chemical increasing viral infection rates, scientists did find that exposure could exacerbate an existing infection, resulting in more harmful health impacts when exposed to both pyriproxyfen and Zika together.
The scientists note that similarly concerning findings have been made for other diseases and pesticides on the market. A study published in October 2020 found that the commonly used fungicide fludioxonil has the potential to decrease human immune defenses against Covid-19. Subsequent research published in February of this year found that Covid-19 vulnerability could increase with exposure to organophosphate pesticides.
Although the public is generally familiar with the concept of pesticides causing specific health outcomes like cancer, there is a growing body of science showing how pesticides can exacerbate certain illnesses, or cause a range of deleterious impacts in the environment that ultimately lead to human disease.
As the author’s write, “…for many other ubiquitous pesticides to which we are continuously exposed in our daily life, we have no clue as to how they affect us, and whether they interact with viral diseases… Our study emphasizes again how little we know about the harmful effects of pesticides on human health, notably on brain development, but also the natural environment as a whole.”
Take action to tell EPA to consider cutting edge science in agency decision makings, and follow the precautionary approach when deciding whether to register a pesticide.
Proper mosquito management does not rely on the use of any one particular product but takes a holistic, ecological approach that places emphasis on nontoxic practices first. This includes an emphasis on mosquito monitoring and surveillance, public education, ecological analysis, and habitat alterations. Toxic synthetic larvicides and insect growth regulators like pyriproxyfen should be eschewed in favor of biological materials like Bacillus thuringiensis israelensis (Bti). Adulticides should always be a last resort and used only in the sustained presence of a disease vector. For more information about safer mosquito control, see Beyond Pesticides webpage on Mosquito Management and Insect-Borne Diseases.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Environmental Pollution, The Conversation
