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.” ||||| “It’s pretty obvious that in all seven sites there is a clear relationship,” said Dr. Marcos A. Espinal, the study’s lead author and the director of communicable diseases at the Pan American Health Organization, which collected data on confirmed and suspected cases of Zika infection and on the incidence of Guillain-Barré. “Something is going on.” 
 
 In Venezuela, officials expected roughly 70 cases of Guillain-Barré from December 2015 to the end of March 2016, as mosquitoes were spreading the virus. Instead, there were 684 cases. 
 
 Similarly, during five months in which the Zika virus was circulating in Colombia, officials recorded 320 cases of Guillain-Barré when there should have been about 100. From September 2015 to March 2016, while Zika infections peaked in El Salvador, cases of Guillain-Barré doubled to 184 from 92. 
 
 The researchers included patients with both suspected and confirmed Zika infections, as reported by national health officials. 
 
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 Dr. Kenneth C. Gorson, professor of neurology at Tufts University School of Medicine, who was not involved with the new analysis, called it compelling. 
 
 “This is a substantial public health burden for countries that may not have well-developed health systems in place,” he said. “They have to have enough ventilators and I.C.U. beds.” About one-third of patients with Guillain-Barré require breathing assistance, he said. 
 
 Over all, Dr. Espinal and his authors found increases in Guillain-Barré that were two to 10 times what would normally be expected. Roughly 500 million people in Latin America and the Caribbean are at risk for Zika virus infection, so even modest increases in the incidence of Guillain-Barré are worrisome. 
 
 The nations in the study included the Dominican Republic, El Salvador, Honduras, Suriname, Venezuela and Colombia, along with the state of Bahia in Brazil. (National data from Brazil was not available until February 2016.) 
 
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 Collectively, they reported a total of nearly 1,500 cases of temporary paralysis. The reported incidence was 28 percent higher for men and increased with age for both sexes, in line with previous research. 
 
 Temporary paralysis is a potential neurological complication of dengue infection, too. But Dr. Espinal and his colleagues looked for a similar link to dengue and found none. 
 
 Dr. Gorson noted that the continental United States has no formal monitoring system for Guillain-Barré. As the number of Zika cases in Florida and elsewhere increases, he said, “you won’t know if a Guillain-Barré case is related to Zika infection.” 
 
 “We can do it,” he said of such surveillance. But “there’s no funding from Congress to do it.” ||||| 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 ||||| Guillain-Barré syndrome (GBS) is an uncommon sickness of the nervous system in which a person’s own immune system damages the nerve cells, causing muscle weakness, and sometimes, paralysis. Several countries that have experienced Zika outbreaks recently have reported increases in people who have Guillain-Barré syndrome (GBS). 
 
 Current CDC research suggests that GBS is strongly associated with Zika; however, only a small proportion of people with recent Zika virus infection get GBS. CDC is continuing to investigate the link between GBS and Zika to learn more. 
 
 Symptoms of GBS 
 
 GBS symptoms include weakness of the arms and legs and, in severe cases, can affect the muscles that control breathing. 
 
 These symptoms can last a few weeks or several months. Most people fully recover from GBS, though some people have permanent damage. Very few people die from GBS. 
 
 Causes of GBS 
 
 Researchers do not fully understand what causes GBS. Most people with GBS report an infection before they have GBS symptoms. Rarely, vaccination has also been associated with the onset of GBS (for example, the 1976 Swine influenza vaccine). 
 
 GBS is rare 
 
 An estimated 3,000 to 6,000 people, or 1-2 cases for every 100,000 people, develop GBS each year in the US. Most cases of GBS tend to occur for no known reason, and true “clusters” of cases of GBS are very unusual. 
 
 What to do if you are concerned 
 
 If you want to know more about the number of GBS cases in a certain area, contact the state or local health department in the state where the cases happen. CDC collaborates with state and local health departments to investigate reports of possibly unusually large numbers or “clusters” of GBS cases. 
 
 Additional Resources 
 
 Vaccine Safety Concerns- Guillain-Barré Syndrome 
 
 Guillain-Barré syndrome and Flu Vaccine: Questions and Answers ||||| A rare tropical disease called Zika has made its way to the Americas recently, causing a big outbreak in Brazil and spreading to at least eight other countries. 
 
 Scientists are still learning about this disease, which has long been thought to be pretty mild. But it's getting attention because Zika has also been linked to several deaths and terrible birth defects like microcephaly, which causes babies' brains and heads to stop growing to full size. 
 
 Though it's still not known whether the virus caused any of this, the World Health Organization and its regional outfit the Pan American Health Organization (PAHO) are warning doctors and patients to be on the lookout for Zika. Here's what we know and don't know so far. 
 
 What do we know about Zika? 
 
 The Zika virus is transmitted to humans by the same type of mosquito (Aedes) that transmits the dengue and chikungunya viruses. 
 
 Zika produces very mild symptoms — rash, headaches, pain in the bones, and fever — that usually show up between three and 12 days after a mosquito bite. These symptoms usually go away within a week, and one in four people don’t even develop any symptoms after being infected with the virus. 
 
 This means people don’t usually go to the doctor for Zika, and many cases go unnoticed. There’s also no vaccine or treatment for the virus, so doctors just work on controlling and alleviating its symptoms. 
 
 
 
 Part of the reason the virus hasn't gotten a lot of attention is that the mortality rate for Zika is also extremely low, and researchers don't think of it as a very deadly virus. Though Zika was first discovered in 1947 (in the Zika forest in Uganda), it hasn't bothered humans much in all these years. "There have only been about 14 or 15 cases documented until 2007," said Dr. Marcos Espinal, the director of communicable diseases at PAHO. That's when there was the first big Zika outbreak, reported in the Yap Island in Micronesia. Other Pacific Islands — Fiji, Vanuatu — and Australia have had periodic outbreaks since. 
 
 In 2014, the virus made an appearance in the Americas, arriving in the Easter Islands, and since then it’s shown up in nine countries, including Mexico and Brazil. 
 
 On December 1, PAHO issued an alert about the threat to the Americas, asking public health officials and doctors to be on the lookout for cases. 
 
 There's a risk that people or mosquitoes carrying the disease will come into the US, so you might be hearing more about Zika in the news very soon. 
 
 What don’t we know? 
 
 Because it's so rare and hard to detect, there's still a lot to learn about Zika. 
 
 The most pressing question about the virus is whether it causes serious developmental disorders like microcephaly, the congenital condition that's associated with a small head and incomplete brain development. 
 
 There's a bit of panic about this link in Brazil right now because some of the regions with the most Zika cases have also seen an uptick in microcephaly births. 
 
 Espinal said that researchers from the CDC and the Brazilian health authorities are investigating the link, but right now it's unclear whether the two are related. He explained that microcephaly can be caused by many different factors — including other viruses or Down syndrome — and researchers still don't know whether Zika can even cross the placental barrier in mothers. 
 
 "There’s an ecological link there, but causality is very difficult to determine and we need more research," he added. 
 
 There’s a chance that Zika causes Guillain-Barré syndrome, a very rare neurological syndrome that's been showing up in some Zika patients. But again, all researchers have now is a potential link — and more research needs to be done. 
 
 Finally, there may be more to learn about how deadly Zika can be. Researchers have long believed Zika is a mild virus. (As one microbiologist put it, it's "a lamb, not a lion.") But the virus has been linked to at least seven deaths in Brazil as of November 30. Again, correlation is not causation. As Espinal said, "Zika has a very, very low mortality rate." But it's possible this virus is deadlier than scientists previously thought. 
 
 Why are people talking about Zika now? 
 
 Because of the current outbreak in Latin America. In February 2014, Zika was detected in Chile on Easter Island. In May 2015, Brazil confirmed its own cases. As of this October, there have been more than 1,200 cases in 14 states in Brazil. Colombia, El Salvador, Guatemala, Mexico, Paraguay, Panama, Suriname, and Venezuela have recently reported cases, too. 
 
 So that’s why the PAHO just issued an alert about the threat, telling countries to be on the watch for the disease and any unusual birth patterns with babies. 
 
 Only about 1,000 of the 60,000 cases so far have been confirmed, said Espinal, "so it's important to strengthen surveillance for Zika — to do surveillance and look for congenital abnormalities." Countries are also being advised to take measures to destroy mosquito breeding sites and raise public awareness about the virus. 
 
 Is it true moms in Brazil should avoid having babies? 
 
 There's a lot of panic in the news right now, especially in Brazil. Some local health officials have reportedly suggested that women there avoid getting pregnant until more is known about Zika. 
 
 Espinal said there's just not enough evidence right now to justify avoiding pregnancy. PAHO is recommending pregnant women follow up with their doctors but nothing more drastic. "There’s no need to panic. We need to evaluate the data because we don't know the answers to many questions about Zika. We don't even know if the virus crosses the placental barrier." 
 
 How can you protect yourself? 
 
 There are no travel restrictions for countries experiencing Zika outbreaks, but public health officials are suggesting the following for those in affected regions:
– Earlier this month, Puerto Rico announced its first death from Guillain-Barre syndrome, a condition causing temporary paralysis that, in this case, was linked to the Zika virus. Now incidences of Guillain-Barre are said to have risen in seven countries in tandem with outbreaks of Zika, per a study in the New England Journal of Medicine. The New York Times notes that while the CDC remains wary of saying Zika can cause GBS (it simply says GBS is "strongly associated" with Zika), this research offers further evidence that Zika may indeed be responsible—worrisome news, as about 500 million people in Latin America and the Caribbean are vulnerable to becoming infected with it. "It's pretty obvious that in all seven sites there is a clear relationship," says lead author Dr. Marcos A. Espinal of the Pan American Health Organization. The study found nearly 165,000 cases of Zika virus (some confirmed, some suspected) between April 2015 and March 2016, as well as almost 1,500 cases of GBS, reported in the Brazilian state of Bahia, Colombia, the Dominican Republic, El Salvador, Honduras, Suriname, and Venezuela. During the weeks of Zika outbreaks in these areas, the incidence of GBS cases spiked compared to pre-Zika baseline numbers—jumping as much as 877% in Venezuela. Women had a 75% higher reported incidence rate of Zika than men, but men had a GBS incidence rate 28% higher than women's, and incidence rates also climbed with age, NBC News reports. (The CDC's Zika funds are almost gone.)