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What’s behind the microcephaly outbreak in Brazil? It’s complicated, and it might not be Zika

Angelica Pereira feeds her daughter Luiza, who was born with microcephaly in Santa Cruz do Capibaribe, Brazil, Feb. 6, 2016. (AP Photo/Felipe Dana)

As the Zika virus continues its spread across the Americas, concerns are escalating for pregnant women and their unborn babies. The mosquito-borne virus is widely suspected to cause microcephaly, a condition characterized by an underdeveloped skull and brain, which has been reported in Brazil in record-breaking numbers.

The connection between the two is, at this time, suggestive. Researchers have recently found traces of the virus in the amniotic fluid, brains or spinal fluid of 17 fetuses and babies diagnosed with microcephaly, and Brazil’s Health Minister, Marcelo Castro, has gone so far as to say that he is 100 percent certain that there is a link between the two.

But as researchers around the world scramble to confirm a causal relationship between the two, an alternative explanation for Brazil’s rise in birth defects has come into consideration.

A new report published by the Argentine doctors’ organization, Physicians in the Crop-Sprayed Towns (PCST), points to the Ministry’s failure to recognize that in the area where most Zika-infected people live, a new chemical larvicide was introduced into the water supply in 2014.

This pesticide, pyriproxyfen, is used in a state-controlled program aimed at eradicating disease-carrying mosquitoes, according to The Ecologist. The larvicide is a growth inhibitor of mosquito larvae, which alters the development process to generate malformations in developing mosquitoes to effectively kill or disable them.

The WHO lists pyriproxyfen as a relatively low-risk chemical, and tests carried out in a variety of animals by Sumitomo found that it did not cause birth defects, according to The Ecologist, in the mammals it was tested on. But pyriproxyfen’s effects on the developing human fetus have yet to be tested or confirmed.

The PCST wrote: “Malformations detected in thousands of children from pregnant women living in areas where the Brazilian state added pyriproxyfen to drinking water are not a coincidence, even though the Ministry of Health places a direct blame on the Zika virus for this damage.”

The PCST’s findings have been echoed by a separate report on the Zika outbreak by the Brazilian doctors’ and public health researchers’ organization, Abrasco, which condemns the strategy of chemical control of Zika-carrying mosquitoes. According to Abrasco, pyriproxyfen is not only a possible cause of microcephaly, but is contaminating the environment as well as people and is failing to control the mosquito population.

Until now, Zika has so far been regarded as a relatively benign disease that only sometimes shows symptoms, and has never before been directly associated with birth defects. Now, skeptics of the link between Zika and microcephaly are also questioning whether some media coverage is also blowing the situation out of proportion.

Late last month, Nature published segments of a report that attributed a portion of Latin America’s increase in microcephaly to active search and overdiagnosis. This trend is likely spurred by heavy media coverage of the story and a bulletin published by the Brazilian government at the end of 2015, according to Global Post, which urged physicians to be on the lookout for microcephaly.

Several media outlets have reported over 4,000 cases of microcephaly in Brazil since the start of the outbreak in October, but that number only reflects the suspected cases (infants with abnormally small heads in gestation), some of which end up developing normally. Since October, 404 cases of microcephaly or other nervous system disorders have actually been confirmed, Brazil’s Ministry of Health said on Tuesday, and 709 cases have been ruled out. The other cases remain under investigation.

Amid the uncertainty surrounding the cause of the mysterious rise in birth effects, it remains unknown how these false diagnoses of microcephaly may have affected, and will continue to affect, pregnant women who are told their child may have birth defects. Increasing numbers of women have sought to terminate their pregnancies in Brazil, where abortion is illegal, after being told they contracted the Zika virus or that their unborn baby would likely be born with microcephaly.


About Author

Lisa Nikolau

Lisa Nikolau is a Madrid-based reporter for Humanosphere, covering gender equality, indigenous rights and poverty in Latin America and worldwide. Find her on Twitter at @lisanikolau, email or see her latest work at