There's more evidence that Zika virus infection can cause a paralyzing side effect called Guillain-Barré syndrome.
Instances of Guillain-Barré skyrocketed in countries hit by Zika virus epidemics — by as much as 877 percent in Venezuela, health officials and researchers from Latin America reported. At the very least, rates doubled, the officials said in a letter to the New England Journal of Medicine.
"During the weeks of Zika virus transmission, there were significant increases in the incidence of the Guillain-Barré syndrome, as compared with the pre-Zika virus baseline incidence, in (Brazil's) Bahia State (an increase of 172 percent), Colombia (211 percent), the Dominican Republic (150 percent), El Salvador (100 percent), Honduras (144 percent), Suriname (400 percent), and Venezuela (877 percent)," they wrote. "When the incidence of Zika virus disease increased, so did the incidence of the Guillain-Barré syndrome."
Doctors are fairly certain that Zika can cause Guillain-Barré syndrome, a little understood reaction in which the immune system attacks the nerves. It can cause temporary but often severe paralysis. In extreme cases, patients must be put on ventilators to help them breathe until they recover.
It can be fatal — Guillain-Barré caused by Zika killed a man in Puerto Rico last month. It's usually seen in about every 5,000 to 10,000 infections like Zika. Other infections also can cause Guillain-Barré.
Zika's worst effect is the brain and nerve damage it causes in developing fetuses. It can devastate the growing brain and there is no way to prevent or reverse the effects.
Pregnant women in Zika-affected zones are warned to avoid mosquito bites if they possibly can by using repellents, covering up with clothing and staying inside behind screens and air conditioning. But these facilities are often not available in some of the worst-hit places.
The researchers found more women than men reported Zika infections, but said that might be because women are more aware of the risks because of the pregnancy link. However, men were more likely to develop Guillain-Barré.
"From April 1, 2015, to March 31, 2016, a total of 164,237 confirmed and suspected cases of Zika virus disease and 1,474 cases of the Guillain-Barré syndrome were reported in Bahia, Brazil; Colombia; the Dominican Republic; El Salvador; Honduras; Suriname; and Venezuela," they wrote. "The reported incidence of the Guillain-Barré syndrome was 28 percent higher among males than among females and consistently increased with age, findings that are in line with previous reports."
Zika has often circulated quietly, in part because it doesn't cause symptoms in most people and in part because it looks like so many other mosquito-borne diseases, such as dengue virus.
The health officials suggested that watching for Guillain-Barré cases might be one way to spot Zika outbreaks.
"Approximately 500 million people in Latin America and the Caribbean are at risk for Zika virus infection," they wrote.
"It is clear that increases in the incidence of the Guillain-Barré syndrome to a level that is 2 and 9.8 times as high as baseline, as we have reported here, impose a substantial burden on populations and health services in this region."