The mosquito-borne Zika virus has been linked to a surge in cases of birth defects in Brazil, and is spreading in other countries in the southern hemisphere. Flaminia Catteruccia, associate professor of immunology and infectious diseases at Harvard T.H. Chan School of Public Health, says the virus may have adapted to the human environment and mutated.

What do we know about the Zika virus?

Zika is very similar to other viruses that are transmitted by the Aedes mosquitoes, including dengue and chikungunya. It was first discovered in 1947 in monkeys in Africa, and there have been several outbreaks since then. But it has not been studied much because, normally, the symptoms are quite mild—fever, headaches, joint pain. People get over it in a few days.

It seems like there is something different about the virus in the current outbreak in Brazil. It has coincided with a dramatic rise in cases of microcephaly, a birth defect that results in babies born with unusually small heads. The increase in babies born with this condition has been more than 20-fold compared with previous years—from maybe 150 cases to more than 3,000 cases in a few months.

If Zika is the causative agent behind the surge in microcephaly—and possibly also Guillain-Barré syndrome, an autoimmune disease of the nervous system now on the rise among adults in Brazil—this may demonstrate that the virus has adapted to the human environment and may have mutated to become more pathogenic to humans.

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