Some people infected with the Zika virus may develop a rare neurological disorder that is similar to multiple sclerosis, a new study from Brazil suggests.
The study reports two cases of people who were infected with the Zika virus and who later developed a condition called acute disseminated encephalomyelitis (ADEM). In people with this condition, the body's own immune system causes swelling in the brain and spinal cord, and damages the protective coating of nerve fibers called myelin.
The condition is similar to multiple sclerosis (MS), which also causes damage to myelin. But whereas people with MS often have multiple attacks, people with ADEM usually have just a single attack of symptoms and recover after about six months.
The study adds to a growing list of conditions already linked with the Zika virus, including another neurological disorder called Guillain-Barré syndrome, as well as microcephaly, a birth defect in which an infant's head is abnormally small and is thought to occur when the virus is passed from a woman to her infant during pregnancy.
Still, the new study found only an association between the Zika virus and ADEM, and thus cannot prove that Zika virus infection causes ADEM. It's also important to note that neither Guillain-Barré syndrome nor ADEM is common in people with Zika virus infections, the researchers said. [Zika Virus FAQs: Top Questions Answered]
"This doesn't mean that all people infected with Zika will experience these brain problems," Dr. Maria Lucia Brito Ferreira, a co-author of the new study and a physician at Restoration Hospital in Recife, Brazil, said in a statement. "However, our study may shed light on possible lingering effects the virus may be associated with in the brain."
The study included 151 people who visited a hospital in Recife between December 2014 and June 2015, and who had symptoms of Zika virus or another similar virus. Of these, six people developed symptoms of autoimmune disorders, in which the patient's own immune system mistakenly attacks the body. It turned out that four of these patients had Guillain-Barré syndrome, and two had ADEM, the researchers found. (All six of these patients tested positive for Zika virus.)
For some of these people, neurological symptoms started as soon as the Zika virus symptoms appeared, but for others, the neurological symptoms took up to 15 days to appear.
The study will be presented at the American Academy of Neurology meeting in Vancouver, which runs from April 15 to 21.
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