Researchers at Johns Hopkins Medicine working with scientists in Colombia have discovered what they believe is the strongest evidence yet that the Zika virus causes neurological problems in adults.
Much of the research on the mosquito-borne Zika has focused on pregnant women, because the virus can cause microcephaly in fetuses, causing babies to be born with brain damage and abnormally small heads.
The new research shows that the health effects might be more widespread.
Hopkins researcher Dr. Carlos A. Pardo said the research, published Wednesday in the New England Journal of Medicine, bolsters concerns that Zika can lead to the neurological disorder Guillain-Barre in adults. Until now, the virus was thought to be linked to the disorder only in rare cases.
Guillain-Barre is a nervous system disorder in which a person's immune system attacks the nerves, in the worst cases eventually paralyzing the whole body.
The exact cause of the disorder is not known, but research has found its symptoms often erupt after a viral or bacteria infection. It affects one or two out of 100,000 people who first suffer from infections.
Most people recover from the disorder, but some side effects — such as weakness or numbness — may persist. Research has shown that Guillain-Barre can lead to vision problems in some people.
The Hopkins findings come a week after Congress allocated $1.1 billion for research and aid to fight the spread of Zika as scientists across the world discover more about its effects on people's health.
Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, has said health officials are becoming more concerned about the disease the more they learn about it.
Researchers are beginning to believe that even babies born without microcephaly may suffer problems after birth.
The CDC reports that there have been 3,625 cases of Zika in the mainland United States, and another 22,000 in U.S. territories such as hard-hit Puerto Rico. There have been 808 confirmed cases in pregnant women in the continental United States. Twenty-one babies have been born with birth defects and five pregnancies have been lost.
In Maryland, there have been 101 cases, including 43 in Baltimore and the five surrounding counties and 51 in the Maryland suburbs of Washington.
Pardo, an associate professor of neurology and pathology at the Johns Hopkins School of Medicine, said doctors in Colombia contacted him during the early stages of the Zika outbreak there in the fall of 2015 with concerns about patients suffering from neurological complications.
The researchers in Colombia took cerebrospinal fluid, blood and urine samples from 68 people with Guillain-Barre symptoms at six hospitals.
Of those, 42 were sent to one main laboratory in Colombia, where virus and immunology studies were conducted to see if any had Zika. The scientists determined urine to be most reliable in making a diagnosis because the virus lasted longer in urine than in other bodily fluids.
They found that 17 patients tested positive for Zika and another 18 had Zika antibodies in their blood or spinal fluid, indicating the person might have been exposed to the virus. Just about all of the patients showed two or more Zika symptoms, including fever, headache and rash.
There was evidence that Guillain-Barre developed faster from a Zika infection than from other infections such as influenza or herpes, Pardo said. Nearly half of patients complained of neurological symptoms within four days of Zika symptoms.
Researchers made the link between Zika and Guillain-Barre in 2013 after an outbreak in French Polynesia. About 32,000 people were infected by the Zika outbreak, and 42 patients were confirmed to have Guillain-Barre, a 20-fold increase over the previous four years. Thirty-two other patients showed other neurological disorders, such as facial paralysis or encephalitis.
In a paper published in the journal Lancet that year, the researchers said they found evidence of Zika antibodies in the 42 cases. Antibody tests are limited because they can't determine fully if Guillain-Barre was caused by the Zika virus or another ailment, such at the mosquito-borne dengue virus.
The CDC also released a report in September that described 56 suspected cases of Guillain-Barre in Puerto Rico in the first six months of this year. Of those, 34 were determined to have Zika and treated. The number of patients with both disorders was 2.5 percent greater than those with Guillain-Barre and no signs of Zika.
Dr. Matthew B. Laurens is director of the international clinical trials unit within the Division of Malaria Research at the Institute for Global Health at the University of Maryland School of Medicine.
He said the Hopkins research is the most comprehensive to date on the link between Guillain-Barre and Zika.
"We know viral illnesses can cause Guillain-Barre, but this is evidence there is a very strong link between Zika and Guillain-Barre," Laurens said. "It is documenting the burden of disease of Guillain-Barre in this population that is experiencing a Zika outbreak."
Laurens said the findings could help countries prepare for the disorder. Many small hospitals in poorer countries likely don't have the medication to treat it. The medication, intravenous immunoglobulin, is readily available in developed countries. Poorer countries might now keep some in stock.
Laurens said researchers need to know all the side effects of Zika before testing a vaccine on healthy people. They would not test it on a healthy person if it could cause Guillain-Barre.
The Hopkins researchers have not yet studied how the Zika virus leads to Guillain-Barre. That's something they now plan to look at, using samples collected by the Colombian scientists. The scientists will use mini-brains, microscopic spheres made up of the main components of the brain, to study the connection between the two diseases.
"We will look at what happens to the cells when exposed to the virus," said Dr. Paula Barreras, a Johns Hopkins fellow working on the research.
Pardo said collaboration with the Colombia doctors enabled them to turn around research results quickly. Hopkins provided the Colombians with a kit filled with test tubes to collect the samples. They also created a database in which the Colombians could enter information about each infected patient.
The lack of resources in poorer countries often makes such research cost-prohibitive, Pardo said.