MIAMI - Researchers have found more evidence linking the mosquito-borne Zika virus to a neurological disorder known as Guillain-Barre syndrome, but proof of cause-and-effect remains elusive, a study said Wednesday.
The findings in the New England Journal of Medicine were based on research at six different hospitals in Colombia, involving 68 people with Guillain-Barre syndrome, most of whom had previous symptoms of Zika infection including rash, fever, headache and red eyes.
After a close analysis of these cases, researchers at Johns Hopkins University reported "the strongest evidence to date" of an association with Guillain-Barre, a rare disorder of the nervous system that can result in paralysis.
Nearly half of those in the study "complained of neurologic symptoms within four days of the onset of Zika symptoms," said the study, noting this response was unusually fast compared with those who develop Guillain-Barre symptoms after other viral infections, such as influenza or herpes.
A total of 46 patients were confirmed to have Guillain-Barre by electrodiagnostic neurological tests, and most had a specific variant in which the infection attacks protective cells known as myelin, which insulate the surface of the nerve fibers.
Guillain-Barre occurs in about one in 100,000 people, and usually appears days to weeks after infection with viruses or bacteria.
When Guillain-Barre strikes, a person's own immune system "attacks the myelin sheaths that protect the body's nerve cells, often resulting in muscle weakness, pain, sensory deficiencies and, in very acute cases, paralysis," explained the study.
Experts still do not know why it strikes some people but not others.
In order to prove whether or not Zika causes Guillain-Barre syndrome, or to understand the biological mechanisms at play, more research is needed.
Researchers have previously shown that Zika can cause brain defects such as microcephaly, or unusually small heads, in infants born to infected pregnant women.