The mosquito-borne virus is already suspected of causing a birth defect called microcephaly -- characterized by an abnormally small head and brain -- and a nervous system disorder called Guillain-Barre syndrome.
Now, a new study reports a possible link between Zika and an autoimmune disorder known as acute disseminated encephalomyelitis (ADEM). In this disease, the immune system attacks the coating (myelin) around nerve fibers in the brain and spinal cord, much like multiple sclerosis.
"Though our study is small, it may provide evidence that in this case the virus has different effects on the brain than those identified in current studies," said study author Dr. Maria Lucia Brito Ferreira, of Restoration Hospital, Recife, Brazil.
The study results, released April 10, will be presented April 15 at the annual meeting of the American Academy of Neurology in Vancouver, Canada. Research presented at meetings should be viewed as preliminary until published in a peer-reviewed medical journal.
"Much more research will need to be done to explore whether there is a causal link between Zika and these brain problems," Ferreira added in an academy news release.
In Guillain-Barre, the immune system attacks the nervous system, resulting in muscle weakness and sometimes paralysis, according to the U.S. Centers for Disease Control and Prevention.
Zika, which is prevalent in Latin America and the Caribbean, is mainly transmitted through the bite of infected Aedes aegypti mosquitoes. Most healthy people infected with the virus experience no symptoms, but babies whose mothers were exposed to the virus in pregnancy appear to be at special risk for microcephaly.
The new research indicates the virus might have implications for others as well.
The new study focused on six people who developed neurologic symptoms after arriving at a hospital in Recife between December 2014 and June 2015. All reported symptoms consistent with the family of viruses that includes Zika, dengue and chikungunya. These symptoms included fever followed by a rash, and in some cases, severe itching, muscle and joint pain and red eyes.
For some people, the neurologic complaints started right away; in others, symptoms started up to 15 days later, researchers said.
Of those six patients, two developed ADEM and four developed Guillain-Barre syndrome. When discharged from the hospital, five patients still had movement problems, one still had vision problems and one still had memory and thinking problems.
All six tested positive for Zika, but none tested positive for dengue or chikungunya, according to the study.
"This doesn't mean that all people infected with Zika will experience these brain problems. Of those who have nervous-system problems, most do not have brain symptoms," Ferreira said. "However, our study may shed light on possible lingering effects the virus may be associated with in the brain."
The CDC's Dr. James Sejvar said it does not seem that ADEM cases are occurring as frequently as the Guillain-Barre cases. However, "these findings from Brazil suggest that clinicians should be vigilant for the possible occurrence of ADEM and other immune-mediated illnesses of the central nervous system," Sejvar said in the news release.
"Of course, the remaining question is 'why' -- why does Zika virus appear to have this strong association with [Guillain-Barre] and potentially other immune/inflammatory diseases of the nervous system?" Sejvar asked.
It's hoped ongoing investigations will shed additional light on this question, he added.
Patients with ADEM usually recover within six months, although the disease can reccur, according to the news release.
The U.S. Centers for Disease Control and Prevention has more on the Zika virus.
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