By MAGGIE FOX From NBC News

Two people suffering from a rare paralyzing condition on the Caribbean island of Martinique had evidence of Zika infection, French doctors reported Thursday.

The case adds to a growing body of evidence that Zika can cause Guillain-Barre syndrome, a paralyzing nerve condition that sometimes develops after infections.

Zika had not been known to cause Guillain-Barre before, but its rapid spread across Latin America and the Caribbean is affecting larger numbers of people than ever have been infected at once before. It’s also strongly suspected of causing a severe birth defect called microcephaly.

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New evidence shows link between Zika virus and temporary paralysis 0:35
Benoît Rozé of University Hospital of Martinique and colleagues reported on two people who became so seriously ill with Guillain-Barre that they spent weeks on ventilators.

“Both patients were found to have Zika virus in their urine at hospital admission,” Roze’s team wrote in the journal Eurosurveillance.

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Both — one a young adult, the second middle-aged — became almost completely paralyzed with Guillain-Barre, a little understood syndrome in which the immune system attacks the nerves. Both lost the ability to breathe independently and were put on ventilators, one for a month, the other for 10 days.

Neither had any other infection known to cause Guillain-Barre, the team reported.

The discovery of Zika in the urine suggests it may be a better place to test than in blood. Other researchers have found this, also.

Martinique, a French territory with 390,000 people, has been hit by Zika along with other Caribbean islands.

The World Health Organization has declared the spread of Zika and its link to microcephaly to be a global health emergency. It’s urging researchers to speed tests that can detect the mosquito-borne virus quickly.

Related: Zika Mysteries Stump Experts

U.S. government researchers are working with drug companies to speed a Zika vaccine to market, and officials from Brazil to Texas are trying to eradicate the mosquitoes that spread the infection.

The Centers for Disease Control and Prevention says pregnant women or women who might become pregnant should avoid any area where Zika is spreading, and says men traveling from Zika-affected areas should use condoms after they return to avoid infecting sex partners.

Anyone living in a Zika zone should use mosquito repellent, wear long-sleeved clothing and try to stay in air-conditioned areas to prevent mosquito bites.