The Zika virus has already been linked to serious birth defects in the brain, and now it looks as if the virus may also cause deformities of joints in the arms and legs of newborns, a new Brazilian study suggests.
The condition -- called arthrogryposis -- causes multiple joints to be contracted or curved. This condition hadn't previously been linked to Zika, although two previous reports suggested there might be an association with the virus, researchers said.
The study authors still can't say for sure that Zika caused the arthrogryposis. But all of the babies had the pattern of abnormalities on their brain scans that would be expected with a congenital Zika syndrome, said lead researcher Dr. Vanessa van der Linden. She's with the Association for Assistance of Disabled Children in Recife, Brazil.
The researchers don't know exactly how Zika might cause these deformities. But van der Linden said that in the current cases, the arm and leg defects weren't caused by problems in the joints themselves. Instead, the researchers suspect that problems in nerve cells that control movement caused the babies to stay in fixed positions in the womb, which led to the deformities.
Until recently, no reports of an association between a congenital (from birth) viral infection and arthrogryposis had been seen, van der Linden said.
The Zika virus is typically transmitted via mosquitoes, and is especially dangerous during pregnancy because it can cause the birth defect microcephaly -- where babies are born with a small head and underdeveloped brain. Thousands of such cases have been reported in Latin America, especially Brazil.
Florida is the only U.S. state with known cases of locally acquired Zika infection -- 16 so far.
For the new study, van der Linden and her colleagues studied brain and joint images of seven children with arthrogryposis in Brazil. All the children had been diagnosed with a congenital infection, most likely caused by the Zika virus.
The children were also tested to rule out five other main infectious causes of microcephaly -- toxoplasmosis, cytomegalovirus, rubella, syphilis and HIV. None of the children had these infections.
Brain scans showed that all of the children had signs of brain calcification, a condition in which calcium builds up in the brain. One theory is that Zika virus kills brain cells and forms scar-like lesions in the brain on which calcium is deposited, the researchers said.
The children had scans of their joints and surrounding tissues. No evidence of joint abnormalities was found, van der Linden said.
Based on these findings, "congenital Zika syndrome should be added to the diagnosis of congenital infections and arthrogryposis," she said.
The outlook for children with arthrogryposis isn't promising, said Dr. Arielle Hay, an attending physician in the division of pediatric rheumatology at Nicklaus Children's Hospital in Miami.
"There is some treatment available in terms of physical therapy, casting and surgery, but some of those treatments can make it worse," Hay said.
When the cause is neurological due to a virus, "these kids need lifelong follow-up, there is no definitive treatment, unfortunately," she said.
Dr. Amesh Adalja is a clinical assistant professor in the department of critical care medicine at the University of Pittsburgh Medical Center. "This study adds to the increasing evidence that Zika has a particularly severe impact on a developing fetus that extends beyond just microcephaly," he said.
That the association with arthrogryposis doesn't come from the joints but from nerves is not surprising as Zika has proven to have a strong affinity for nerve cells, Adalja said.
"Follow-up studies to determine the exact mechanism responsible for these complications -- and to firmly identify Zika as a cause -- will be needed," he said.
"As the Zika outbreak matures, it will not be surprising if more congenital abnormalities are discovered to have an association with Zika infection," Adalja added.
The new report was published Aug. 9 in the journal BMJ.