Is Microcephaly in Children Caused by the Zika Virus or by Pesticides?

A crop duster plane spraying fungicide to protect the 7,000 hectare banana plantation of Tagum Agricultural Development Co. from destructive leaf virus in Tagum in Davao del Norte province, located in the southern Philippine island of Mindanao, on April 22, 2008. Farm chiefs have a narrowing chance to diversify vital crops at rising threat from drought, flood and pests brought by climate change, food researchers warned on Oct. 3, 2011. The world's nearly seven billion people are massively dependent on a dozen or so crops that, thanks to modern agriculture, are intensively cultivated in a tiny number of strains, they said. Romeo Gacad/AFP/Getty Images

At the end of October 2015, the Brazilian state of Pernambuco, located in the northeast of the country, started reporting a dramatic increase in the number of babies born with microcephaly, a condition characterized by a shrunken head and brain. The cases in Pernambuco were soon followed by similar ones in the nearby states of Bahía and Paraíba.

The cases of microcephaly seemed to be connected to an outbreak of the Zika virus, first recognized in Uganda in the 1940s. Zika is transmitted by Aedes aegypti, a species of mosquito that thrives in stagnant water pools. In the same way as malaria, dengue, and Chikungunya, the Zika virus infection results in similar symptoms: fever, joint pain, and rashes.

Thus, ominously, parallel to the increased number of pregnant women infected with the Zika virus there was an increase of microcephaly cases in their children. Because CT scans of those babies’ brains showed signs of calcification usually associated with an infectious disease rather than a genetic abnormality, many experts thought that their microcephaly was caused by the Zika virus.

Although a causal link between Zika infection in pregnancy and microcephaly has not ... been established, the circumstantial evidence is suggestive and extremely worrisome.

— Dr. Margaret Chan, director-general, WHO