Disease specialists in Brazil say the Zika virus may be causing a surge in the potentially life-threatening Guillain-Barré syndrome.

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RIO DE JANEIRO — A mosquito-borne virus that has been linked to severe brain damage in infants may be causing another serious health crisis, Brazilian officials and doctors warn, citing hundreds of cases of a rare syndrome in which patients can be almost completely paralyzed for weeks.

The Zika virus arrived in Brazil recently but is spreading rapidly around Latin America and the Caribbean. Nearly 4,000 cases of brain damage, in which babies are born with unusually small heads, have been registered in Brazil in the past year, and this month U.S. officials warned pregnant women to delay traveling to nearly 20 countries in the Western Hemisphere and Puerto Rico, where mosquitoes are spreading the virus.

But disease specialists in Brazil say the virus may also be causing a surge in another rare condition, known as Guillain-Barré, a potentially life-threatening syndrome in which a person’s immune system attacks part of the nervous system, leaving some patients unable to move and dependent on life support. Most people with Guillain-Barré recover.

Until recently, the condition was so rare that Brazil’s Health Ministry did not require regional officials to report it. But last year, the authorities in northeast Brazil, the region hit hardest by the Zika virus, counted hundreds of Guillain-Barré cases, prompting doctors to sound the alarm.

“Guillain-Barré can be a nightmare for those who have it,” said Dr. Wellington Galvão, a hematologist in Maceió, in northeast Brazil, who treated 43 patients with Guillain-Barré in 2015, up from an average 10 to 15 cases in previous years. “I estimate that Zika increases by about 20 times the probability that an individual can get Guillain-Barré.”

Shortly after a mosquito infected Patricia Brito with the Zika virus, she knew something was terribly wrong. Soon she could not move her legs. The paralysis soon spread to the rest of her body, and doctors put her on a ventilator in an intensive-care unit for 40 days.

“It was more terrifying than any horror movie,” said Brito, 20, who works as a cashier at a bakery in Delmiro Gouveia, in northeast Brazil. Months after her release from the hospital, Brito still does physical therapy in an effort to avoid using a wheelchair.

Researchers caution that more studies are needed to prove the link between Zika and Guillain-Barré. A spokesman for the Centers for Disease Control and Prevention (CDC) in the United States said, “Reports must be treated as anecdotal because little pertinent supporting diagnostic information is available.”

Nonetheless, the CDC is viewing Guillain-Barré as a serious risk. It is helping Brazil conduct a study this month to evaluate if any link exists between the condition and the Zika virus.

Last week, the CDC confirmed the presence of the Zika virus in a baby born with an unusually small head and brain in Hawaii, the first case of brain damage linked to the virus in the United States. The mother had been in Brazil while she was pregnant. But the CDC added that it had not found an increase in Guillain-Barré cases in any U.S. territory, including Puerto Rico.

Camila Bogaz, a spokeswoman for Brazil’s Health Ministry, cited a recent study by the Federal University of Pernambuco showing that some patients with Guillain-Barré syndrome had previously been infected with Zika. But she, too, cautioned that the connection between Zika and Guillain-Barré was still under investigation.

Outside Brazil, other countries in Latin America where Zika is spreading are reporting an increase in cases of Guillain-Barré, including Colombia and Venezuela. This month, El Salvador said it was seeing a surge in Guillain-Barré cases. It normally averages about 14 a month, but between Dec. 1, 2015, and Jan. 6, 2016, it recorded 46; two of them died.

Of the 22 patients for whom medical histories were available, about half remembered having had the fever and rash that are the most common symptoms of Zika, between a week and two weeks before their paralysis began.

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Guillain-Barré has sporadically been diagnosed as a consequence of a number of viral infections, including other mosquito-borne diseases such as dengue fever, chikungunya and West Nile virus.

“The increase in Guillain-Barré is very similar to what happened when dengue spread rapidly here in 2003 and 2004,” said Dr. Maria Lúcia Brito, a neurologist in Recife in northeast Brazil who treated 50 patients with Guillain-Barré in 2015, up from 14 in 2014 and 13 in 2013. “This makes mosquito-eradication campaigns even more urgent across Brazil.”