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Scientists have been trying to figure out why hundreds of babies in Brazil have been born with small heads, a condition known as microcephaly. The prime suspect is the Zika virus, but there are other theories. A recent report raises the possibility, disputed by many, that the culprit is not the mosquito-borne disease but a mosquito pesticide. NPR's Rae Ellen Bichell reports.
RAE ELLEN BICHELL, BYLINE: The pesticide is called pyriproxyfen. It's sometimes added to water to prevent mosquitoes from hatching and growing. The report from a group of doctors in Argentina says Brazil started using the chemical in drinking water a few months before people noticed an increase in malformations in newborn babies. Dr. Medardo Avila Vazquez is a pediatrician in Cordoba and an author on the report.
MEDARDO AVILA VAZQUEZ: (Through interpreter) It's a hypothesis, a probability, and for us, it's more likely that it's the chemical larvicide and not Zika.
BICHELL: The idea quickly spread through Brazilian media.
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UNIDENTIFIED WOMAN: (Speaking Portuguese).
BICHELL: Health officials in one Brazilian state announced that they would immediately stop using pyriproxyfen in drinking water.
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UNIDENTIFIED MAN: (Speaking Portuguese).
BICHELL: But there is a lot of skepticism about this report. Marcos Espinal, director of communicable diseases and health analysis at the Pan American Health Organization, said this.
MARCOS ESPINAL: So far, there is no evidence suggesting that that could be the problem.
BICHELL: The Zika virus, he said, is guilty until proven innocent. But still, the idea has taken off. One of the main arguments is that if the compound can interfere with insect development, then it might also interfere with human development. But that's not the case, says Bruce Gordon. He's the coordinator of the Water, Sanitation, Hygiene and Health Group at the World Health Organization.
BRUCE GORDON: Pyriproxyfen actually mimics a hormone found in invertebrates, so it basically interferes with their development. But mammals don't have that development process.
BICHELL: So pyriproxyfen couldn't do anything to the human developmental process, he says.
GORDON: There's absolutely no concern for reproductive effects that have been raised for this chemical.
BICHELL: The WHO has come up with a maximum concentration of pyriproxyfen allowed in drinking water, but the concentration required to kill mosquitoes is only a tiny sliver of that - 0.0003 ounces per gallon of water. That's what the Brazilian Ministry of Health direct state and city officials to use in water sources.
GORDON: It's miles below the maximum doses you would apply. I mean, you would have to drink hundreds of liters of water to get anywhere near potentially risky level.
BICHELL: It's unclear how many countries actually use pyriproxyfen in their drinking water. For example, it's approved in the U.S. but only for food crops, lawns and to control fleas and ticks on pets. After the report from Argentina came out, the Brazilian Association of Collective Health known as ABRASCO called on states to stop using pyriproxyfen in drinking water. Dr. Gustavo Bretas is an epidemiologist with ABRASCO. He says what's really needed is not to use pesticides at all but to have better access to drinking water so there aren't stagnant tubs sitting around for mosquitoes to breed in.
GUSTAVO BRETAS: Piping and better tanks, and the tanks have to be protected, have a proper lid and all the gaps are closed.
BICHELL: In the end, though, the most compelling point against pyriproxyfen's role in Brazil's recent health issues is this. Health officials in the state of Pernambuco say that in the three cities with the most microcephaly cases, they don't use the chemical. Rae Ellen Bichell, NPR News.
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