How Zika Virus Works

In late 2015, American media began buzzing with rising concern over a mosquito-borne disease that was old news in Africa and Asia but new to the West. To doctors familiar with this relatively wimpy cousin of dengue fever, chikungunya and yellow fever, the concern might have seemed misplaced, were it not for a series of seemingly related cases of microcephaly that coincided with the virus’s arrival in Brazil.

Fears rose as images of children with abnormally small heads began appearing in the news, accompanied by words like “unusually severe” and “incomplete brain development.” And as it became clear that the Americas, whose lack of Zika immunity was matched by their abundance of mosquito-friendly habitats, were facing an epidemic, it no longer mattered that the virus typically caused only mild flu-like symptoms in a small percentage of infected adults. Proven or not, understood or not, the threat of children being born with microcephaly — or with Guillain-Barré syndrome, another neurological disorder linked to Zika — soon drove calls for “nuclear” options. The mosquitos, said some, had to die, and devil take the consequences.

But wait a minute, said others. What’s actually going on here? Are these neurological disorders truly caused by Zika? If so, what mechanism links the two phenomena, and why have we never heard of this connection before? Is it possible that the link was mere coincidence, or that we are overlooking some vital factor, such as diet or environment? And what about the fact that Zika can be spread through blood, semen or possibly other bodily fluids?

Whatever the case, where Zika has led, dread has followed. On Feb. 1, 2016, the World Health Organization declared Zika a Public Health Emergency of International Concern because of its wide and fast spread in the Americas and its possible link to neurological complications. One week later, the Obama administration said it would ask Congress for more than $1.8 billion in emergency funds to support testing, surveillance, response and containment, and to pursue a vaccine. Some countries, including the U.S., have recommended that their athletes skip the Summer Olympics in Rio de Janeiro. Some, too, have suggested that women put off having children for a few years.

As of early February 2016, Zika had reached epidemic levels in Mexico, the Caribbean, and Central and South America [source: Ungar]. The disease is spreading through 33 countries, home to a total of 600 million inhabitants, suggesting the potential infection of tens of millions [source: McNeil et al.]. There’s no vaccine on the immediate horizon, so, as usual, our best weapon is knowledge.

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