A small number of babies infected with Zika virus in the womb have developed a rare birth defect involving muscle weakness and stiff joints, according to a new report of the cases.
The report suggests that this birth defect, called arthrogryposis, is linked with Zika virus infection in pregnancy, adding to the list of health problems tied to the virus.
Infection with Zika virus in pregnancy has already been found to cause the birth defect microcephaly, which means a child has an abnormally small brain and head. The virus has also been linked with eye problems, hearing loss and impaired growth, according to the Centers for Disease Control and Prevention.
In fact, researchers are now referring to the range of health problems linked to Zika virus infection in the womb as "congenital Zika syndrome," although the researchersare still trying to figure out all of the health problems that this syndrome might involve.
In babies with arthrogryposis and signs of infection in the womb, doctors should consider congenital Zika syndrome as a possible diagnosis, the researchers concluded. [Zika Virus News: Complete Coverage of The Outbreak]
The researchers analyzed information from seven babies who had arthrogryposis and were born in Brazil, the country where the recent Zika outbreak began in early 2015. Arthrogryposis is rare; in the United States, it occurs in about one in every 3,000 live births. The name of this condition literally means "crooked joints" in Greek. Babies with arthrogryposis have restricted movement in some of their joints, and sometimes the joints are stuck in a single position, according to Seattle Children's Hospital.
Six out of the seven babies in the report also had microcephaly, and all of the babies had signs of being infected while they were in the womb. Two of the babies tested positive for Zika virus in their cerebrospinal fluid. The rest of the babies did not receive Zika tests, because the test is not available routinely in Brazil. But the researchers said they presume that all of the babies were infected with Zika, because all of the infants tested negative for other infections that can cause microcephaly. Those infections include the parasite toxoplasmosis; viruses such as cytomegalovirus, rubella and HIV; and the bacteria that cause syphilis.
The babies underwent detailed imaging scans of their joints, but the researchers didn't find any abnormalities in the actual joints. Instead, the children's arthrogryposis likely had a neurological basis, the researchers said. This means the children had problems with the brain and nerve cells that control the contraction or relaxation of muscles around those joints.
Brain imaging showed the children had smaller than normal brains, a buildup of calcium in the brain and underdevelopment of the brain stem, the report said.
The researchers hypothesized that the Zika virus could have caused the neurological problems, which in turn affected the ability of the fetuses to move around inside the womb. Because movement is important for the normal development of the joints and muscles, lack of movement in the womb can lead to arthrogryposis, according to Nationwide Children's Hospital in Columbus Ohio.
It's important to note that the study found only an association between Zika virus infection and arthrogryposis, and does not prove that the virus actually caused this condition. Larger studies of arthrogryposis linked with Zika virus infection are needed in order to better understand the neurological problems that may underlie the condition, the researchers said.
All children with Zika virus infection in the womb should be followed and evaluated for bone and muscle problems, the researchers said.
The study is published today (Aug. 9) in the medical journal The BMJ.
Original article on Live Science.