Zika virus poses a greater threat than we thought

The Zika virus outbreak in South America has caused thousands of cases of microcephaly, where an infant is born with an unusually small head and brain. The threat is so serious that the CDC has issued a level 2 alert for anyone attending the Olympic Games in Brazil this summer. The World Health Organization has also issued travel precautions.

Most of the attention has focused on microcephaly, understandably so, but Zika threatens more than just pregnant women. In recent months, the evidence has been building that Zika also causes Guillain-Barré Syndrome (GBS).

GBS is a rare but terrifying disease, in which your own immune system attacks your nerve cells, leading to rapid paralysis and, in some cases, death. With the best available modern care, the death rate is about 5%, but it's much greater when patients cannot get high-level care.

The first report of Zika as a cause of GBS appeared earlier this year in The Lancet, in a study of a 2013-14 Zika outbreak in French Polynesia (Tahiti). 42 patients were identified with Guillain-Barré syndrome (a startlingly high number for this otherwise rare disease), and 41 of them tested positive for Zika. None of those patients died, but the study provided convincing evidence that Zika was the cause of GBS.

This year, reports have emerged of a sharp increase in the number of cases of Guillain-Barré in South America, where the Zika outbreak is most severe. As the Washington Post reported back in February, the small town of Turbo, in Colombia, which normally sees at most one case per year, has already seen five cases, three of them fatal.

In response to this threat, a group of more than 200 doctors from around the world has signed an open letter to the WHO (read it here) that

"call[s] for the Rio 2016 Games to be postponed and/or moved to another location—but not cancelled—in the name of public health."

The letter points out that Rio is at the epicenter of the Zika epidemic, with 32,000 cases so far, and the holding the games there–with all the associated travel involved–may accelerate the spread of the dangerous Brazilian strain.

The newly emerging risk of Guillain-Barré syndrome makes it clear that Zika virus presents a threat to everyone. The Rio Olympics are likely to make it worse. Anyone planning to visit Rio for the Games should take all the precautions they can, but the best plan might be simply to stay home.