Common mosquito pesticides worsen health problems associated with Zika virus

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(Beyond pesticides, Sept. 28, 2021) A widely used mosquito pesticide could exacerbate the effect of Zika virus on fetal brain development, according to a study published by an international team of scientists in the journal Environmental pollution. Pyriproxyfen, an insect growth regulator often used as a larvicide against mosquitoes, is registered for use in hundreds of commonly used pesticide products. But scientists have found that the pesticide’s mode of action has the potential to worsen public health mosquito diseases that the chemical aims to control. Research reinforces the breadth of unknowns associated with exposure to synthetic pesticides, highlighting the need to focus on non-toxic and environmentally friendly mosquito management.

Scientists base their research on reports that in Brazil, during the 2015 Zika epidemic, some areas of the country experienced higher rates microcephaly. Microcephaly is a rare condition that causes the fetus of pregnant women to develop severe head deformities, along with a range of other symptoms that include vision problems, hearing loss, feeding problems, developmental delays. and seizures. The present study aimed to see how pyriproxyfen, used at higher rates in areas where cases of Zika microcephaly have been recorded, may interact with the virus.

In an article published in The conversation, the researchers note that so far data on pyriproxyfen’s role in the microcephaly epidemic has shown conflicting results. Based on previous research, it was hypothesized that a particular metabolite of pyriproxyfen (4′-OH-PPF), rapidly metabolized in the bodies of humans and wildlife (vertebrates and invertebrates), played a role due to its effects on the thyroid hormone. production. As the study notes, “[thyroid hormones] THs are the key to the evolutionary expansion of brain size and complexity, a hallmark of humans. “

To test this hypothesis, the researchers used genetically engineered tadpoles developed to glow green in the presence of thyroid hormones. Once these tadpoles were dosed with the chemical, their green coloration significantly diminished, indicating that pyriproxyfen was blocking the production of thyroid hormones.

The effects on the thyroid were targeted for analysis due to the essential role that thyroid hormones play in the development of brain cells. In a follow-up experiment, the scientists took stem cells created from mouse brains and exposed them to various levels of the pyriproxyfen metabolite. As the dose increased, so did brain cell death.

The researchers found that the brains of tadpoles exposed to chemical exposure altered gene expression. The focus is on a particular gene – Msi1, which contains the Musaschi-1 protein. Zika uses this protein 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.

“This is why we hypothesized that by increasing Musaschi-1, pyriproxyfen might allow the virus to replicate faster,” the authors wrote in The Conversation. While the study does not support increased rates of viral infection from the chemicals, scientists found that exposure could exacerbate an existing infection, leading to more harmful health effects when exposed to both pyriproxyfen and Zika.

Scientists note that equally worrying discoveries 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 this year found that vulnerability to Covid-19 could increase with exposure to organophosphate pesticides.

Although the public is generally familiar with the concept of pesticides causing specific health effects like cancer, there is a growing body of scientific evidence showing how pesticides can exacerbate certain diseases or cause a series of deleterious impacts on the environment. which ultimately lead to human illnesses.

As the author writes, “… for many other ubiquitous pesticides to which we are continually exposed in our daily lives, we have no idea how they affect us and whether they interact with viral diseases… Our study once again underlines how little we know. on the harmful effects of pesticides on human health, in particular on brain development, but also on the natural environment as a whole.

Act for tell the EPA to consider cutting edge science in agency decision making, and follow the precautionary approach when deciding whether to register a pesticide.

Good mosquito management does not rely on the use of a particular product, but takes a holistic and ecological approach that first emphasizes non-toxic practices. This includes a focus on mosquito tracking and surveillance, public education, ecological analysis, and habitat modifications. Toxic synthetic larvicides and insect growth regulators like pyriproxyfen should be avoided 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 on safer mosquito control, see the Beyond Pesticides webpage on Mosquito Management and Insect-Borne Diseases.

All positions and opinions not attributed in this article are those of Beyond Pesticides.

Source: Environmental pollution, The conversation


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