This week, scientists’ prediction from earlier this year in The Lancet that Zika infection might be strongly correlated with crippling temporary paralysis was corroborated by a study in the New England Journal of Medicine, which found a worrying, sharp increase in the number of people with temporary paralysis in the places where Zika had struck the hardest.

If the correlation is proven to be real — and there’s plenty of evidence to say that it is — infected patients could be in for a devastating few months.

The particular form of paralysis being observed in these countries is called Guillain-Barré syndrome, a mysterious disorder with an unknown set of triggers. It’s broadly understood that paralysis begins when the body’s immune system starts attacking its own nerves — the highways that channel instructions about motion from our brain to our extremities — thereby causing full-body numbness, muscle weakness, and, in the worst cases, complete paralysis. But as for what signals the immune system to turn on itself? Scientists suspect it’s caused by infection with other viruses, though it’s still unclear; there’s mounting evidence, now, that Zika infection might be a trigger.

The onset of the syndrome is slow. Guillain-Barré first manifests as general numbness, which begins in the fingers and toes and creeps back toward the body’s core. Within days, the limbs begin to lose their strength, until even walking becomes difficult. When full paralysis sets in after about two weeks, the patient needs to be hospitalized: In the most extreme cases, even the respiratory system is crippled, making the condition a bona fide medical emergency. If Guillain-Barré is diagnosed early enough, patients are generally intubated and treated with an antibody known as IVIg, which is thought to fight viruses. Unfortunately, because the condition is — or, at least, was — so rare, physicians don’t always consider it when making a diagnosis.

In the NEJM study, the researchers report that the seven countries they examined — all of which experienced recent Zika outbreaks also had sudden increases in the number of people reporting symptoms of Guillain-Barré syndrome. In Venezuela, for example, where public health officials expected to see only 70 cases of Guillain-Barré between December 2015 and March 2016, they counted 684, the New York Times reports. Likewise, the number of cases documented in El Salvador during that same period was double what was originally predicted. Other nations involved in the study included the Dominican Republic, Honduras, Suriname, Colombia, and Bahia, a Brazilian state. Notably, many of these countries do not have the health care systems to deal with numerous cases of Guillain-Barré; treatment is intensive, expensive, and can take over three years for a full recovery.

The CDC has yet to conclude that there’s a cause-and-effect relationship between Zika and Guillain-Barré, but the studies in both The Lancet and the NEJM both point to a correlation that, at the very least, should put physicians in Zika-stricken areas on high alert.

Photos via Theo Heimann/Getty

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.