The Aedes aegypti mosquito carries the Zika virus, which has been linked to suspected brain damage in thousands of Brazilian newborns. (AFP/Getty Images) 
 
 This post has been updated. 
 
 U.S. and Brazilian health officials are investigating whether there may be an association between the mosquito-borne Zika virus that is spreading in the South American country and an increase in cases of a rare syndrome that causes paralysis. 
 
 The Centers for Disease Control and Prevention has sent a four-member team to Brazil to help the health ministry in its investigation of the growing number of cases of Guillain-Barré syndrome and a potential connection to the Zika outbreak there. 
 
 Spokeswoman Christine Pearson said Thursday that the CDC team, dispatched at Brazil’s request, has been on the ground for less than a week. It includes a neuroepidemiologist and a medical epidemiologist. 
 
 [Zika's alarming spread: More than a million infected with virus globally] 
 
 Guillain-Barré syndrome occurs when individuals’ own immune system damages their nerve cells, causing muscle weakness and sometimes paralysis. Symptoms usually last for a few weeks. Most people recover fully from it, but some have long-term nerve damage. In rare cases, people have died, usually from difficulty breathing. 
 
 Brazilian officials have identified hundreds of cases of Guillain-Barré syndrome. A number of states have reported significant increases. Rio Grande do Norte state had reported 33 by August, compared to 23 in the whole of 2014, TV Globo said last month. 
 
 Brazil’s Ministry of Health said in December that it was investigating whether the syndrome could be caused by Zika. The ministry said the symptoms being seen start in the legs, before radiating through the trunk, arms and face. The condition is most dangerous when it involves respiratory muscles. “In this case, the syndrome can cause death if respiratory support measures are not adopted,” the ministry said. 
 
 ["I could move my fingers but within days I'd probably be totally paralyzed"] 
 
 Earlier this week, the Pan American Health Organization and World Health Organization announced an “increase of congenital anomalies, Guillain-Barré syndrome, and other neurological and autoimmune syndromes in areas where Zika virus is circulating.” PAHO warned member states to step up detection, prepare for a possible increase in neurological cases and reduce mosquito transmission. 
 
 Zika is carried by mosquitoes and typically causes only mild symptoms, but health officials globally have recently been alarmed because of a possible link between the virus and nearly 3,900 children born with suspected microcephaly in Brazil since October. The rare condition, marked by an abnormally small head, is associated with incomplete brain development. 
 
 (This video was updated on Feb. 2, 2016.) Authorities have confirmed more than 30 cases of Zika virus in the United States. Here's what you need to know. (Gillian Brockell/The Washington Post) 
 
 Last week, CDC issued an advisory warning pregnant women against travel to Brazil or more than a dozen other countries and territories in South America, Central America and the Caribbean where local transmission of the virus has been confirmed. 
 
 The agency then followed up with guidelines for doctors who care for pregnant women, advising that they be tested for Zika infection if they show symptoms after visiting any of those areas. The guidelines note: “Guillain-Barré syndrome has been reported in patients following suspected Zika virus infection.” 
 
 [How climate change could help the spread of Zika virus and other infectious diseases] 
 
 In recent days, several countries have taken drastic measures to try to combat the Zika virus, with Brazil, Colombia, El Salvador and Jamaica all calling on women to consider delaying becoming pregnant. 
 
 In the United States, Florida, Illinois, New Jersey, Texas and Hawaii have confirmed Zika infections involving returning travelers who were likely bitten by mosquitoes while abroad. The CDC said there have been at least “a dozen or so” cases. 
 
 Ariana Eunjung Cha and Dom Phillips in Rio de Janeiro contributed to this report. 
 
 Read more: 
 
 CDC: 'Dozens or so' cases of Zika virus among U.S. residents 
 
 Brazilians panic as mosquito-borne virus is linked to brain damage in thousands of babies ||||| 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. 
 
 A specialist at Harris County Public Health and Environmental Services holds a box that contains captured mosquitoes. Jennifer Weiss / NBC News 
 
 “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. 
 
 Related: Rare Zika Complication Hits 30 in Puerto Rico 
 
 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. 
 
 “When the incidence of Zika virus disease increased, so did the incidence of the Guillain–Barré syndrome.” 
 
 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.” 
 
 “The reported incidence of the Guillain–Barré syndrome was 28 percent higher among males than among females.” 
 
 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. 
 
 Related: Zika Link to Birth Defects, Guillain-Barré 'Alarming' 
 
 “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.”
– There's more bad news regarding the Zika virus wreaking havoc in South America and the Caribbean: The mosquito-borne virus—which can cause birth defects and has been linked to 46 infant deaths—may also cause Guillain-Barré syndrome, a potentially life-threatening condition that can cause weeks-long paralysis, reports the New York Times. The syndrome attacks a patient's immune system, and though there is no proof of a link, Guillain-Barré was thought to be rare in Brazil until last year when 554 cases were reported in areas worst hit by the Zika virus, per the Telegraph. Colombia, Venezuela, and El Salvador—where women have been warned not to get pregnant—have also seen an increase in Guillain-Barré cases as the Zika virus spreads. Many patients had symptoms of Zika one to two weeks before experiencing paralysis. "I estimate that Zika increases by about 20 times the probability that an individual can get Guillain-Barré," says a doctor who's treated the "nightmare" condition, which strikes about 1 in 100,000. "It felt like I was drowning in a sea of mud," says one patient. "I became motionless and thought I would die. All of this happened just a few days after I had Zika." Another patient had to be put on a ventilator for 40 days once the paralysis reached her breathing muscles. Most people recover from the condition, though some suffer long-term nerve damage, per the Washington Post. The condition, which has previously been associated with mosquito-borne diseases like dengue fever and the West Nile virus, can also lead to heart attacks and comas. The CDC is now researching whether Zika and Guillain-Barré are indeed linked. (A baby born in Hawaii has brain damage linked to Zika.)