Scientists debunk theory linking pesticide, not Zika, to birth defects
Experts debunked a theory this week that linked pesticides to an increase in birth defects thought to be caused by the mosquito-borne Zika virus in Brazil.
The theory gained traction among social media users after Argentine environmentalists issued a report linking the surge to pyriproxyfen, a chemical that kills mosquito larvae.
Pyripyroxyfen interferes with a mosquito growth hormone, preventing the larvae from developing into adults, said biologist Laura Harrington, professor and chairwoman of the entomology department at Cornell University in New York.
Brazil's Ministry of Health rejected any link between the chemical and the microcephaly outbreak, noting the World Health Organization deems pyriproxyfen safe for use as a pesticide.
Pyripyroxyfen has been used for decades, with no reports of increased birth defects, said Ernesto Marques, associate professor of infectious diseases and microbiology at the University of Pittsburgh, who is working in Recife, Brazil to study microcephaly.
"It's ridiculous," said Marques, of the purported link between the chemical and microcephaly. "These guys come out of the blue, and people believe them, with no evidence at all. It really shows the lack of science education among the public."
The WHO has said there is no definitive proof yet that Zika — spread by the Aedes aegypti mosquito — causes microcephaly, a condition where babies are born with abnormally small heads. But researchers say the evidence of such a link is growing stronger.
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Scientists didn't connect the Zika virus, discovered in 1947, to microcephaly until last fall when Brazil reported an increase in the birth defect. Doctors noticed the rise about six months after diagnosing the first cases of Zika, suggesting the virus infected the mothers in their first trimester of pregnancy, a critical time for fetal brain development.
Researchers found genetic material from the virus in the brains, placenta and amniotic fluid of several infants with microcephaly, including ones miscarried or aborted by women infected with Zika while pregnant.
A recent analysis of microcephaly cases in French Polynesia found rates of the birth defect increased there after a Zika outbreak in 2013 and 2014. No one noticed the spike until researchers went back to their records to look for it.
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Research on Zika and the birth defect "overwhelmingly point to a virus as the cause of microcephaly," said Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston.
The Argentine environmental group said on its website that cases of microcephaly have occurred only in places in Brazil where the pesticide has been used. But the Brazilian Ministry of Health said cases have increased across the board — even where the pesticide hasn't been sprayed.
The environmentalists called pesticide spraying from planes a "criminal, useless and a political maneuver" by governments to show they are taking action.
"The reason that the pesticide is found in areas with microcephaly is because it's being used to control Aedes aegypti and Zika," said Grayson Brown, director of the public health entomology laboratory at the University of Kentucky in Lexington. "The larvicide would not be used in areas lacking the mosquito vector. The whole notion is misplaced cause and effect."
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The group opposes the use of genetically engineered mosquitoes, which scientists are testing as a way to reduce the insect population. It called the experiment a "total failure, except for the company supplying mosquitoes."
Brown said the environmentalists "are using this tragedy to promote their own agenda" against pesticide and genetic engineering.
"There's a lot of alarmism going around right now, and we would all benefit if it would get tamped down a bit," Brown said. "It is really quite irresponsible and counterproductive."