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There's new evidence that the Zika virus can cause paralysis

When it comes to Zika, there are many more unknowns than knowns. One big question about the virus has been whether a Zika infection can cause Guillain-Barré, a rare and sometimes deadly neurological condition in which people's immune systems damage their nerve cells, leading to muscle weakness, paralysis, or, in rare cases, death.

New proof of a link with Guillain-Barré was published Monday in the Lancet.

For the study — led by professor Arnaud Fontanet from the Institut Pasteur in Paris — researchers analyzed the blood samples of 42 patients who had been diagnosed with Guillain-Barré during a Zika outbreak in French Polynesia in 2013-'14.

Nearly 90 percent of these patients had reported symptoms of Zika about a week before the neurological symptoms associated with Guillain-Barré began. Blood tests revealed that all 42 people were also carrying Zika virus antibodies, proof of infection.

In a control group, by comparison, only a little more than half of the patients tested positive for the antibodies.

This study comes at a time when countries with Zika outbreaks, including Brazil and Venezuela, have been reporting increases in Guillain-Barré cases.

But not so fast: The evidence is best viewed as a new piece in the puzzle. Since knowledge of this rare disease is so limited, more evidence is needed to establish a definitive link.

In a Lancet commentary related to the new study, professor David Smith of the University of Western Australia explained: "A little caution should be taken because the data are still scarce and we do not know whether the current Zika virus is identical to that in previous outbreaks, whether it will behave exactly the same in a different population with a different genetic and immunity background, or whether a cofactor or co-infection is responsible."

He also noted it wouldn't be the first time a virus had caused Guillain-Barré. Other infections such as herpes, the flu, and dengue have been linked with the neurological syndrome.

Importantly, if a link is established, it's expected to be rare. Based on the Lancet analysis, the researchers estimated that if 100,000 people were infected with Zika, 24 would develop Guillain-Barré.