Zika infection during pregnancy may cause limb joint deformities in the baby, experts now fear.
Brazilian researchers from Recife, the city at the centre of the Zika epidemic, describe seven suspect cases in the journal BMJ Open.
The virus, which has been spreading across much of the Americas and has deterred some people from visiting the Olympic host country, is already known to cause a serious baby brain defect.
Pregnant women should not travel to areas with Zika, and those living in Zika zones should avoid the biting mosquitoes that carry and spread the disease.
Experts now agree that Zika is capable of causing lasting brain damage to babies in the womb. The virus can cross the placenta from the mother to her unborn child.
And there is growing evidence that it can trigger a rare, weakening condition of the nerves, called Guillian-Barre syndrome, in adults.
Dr Vanessa van der Linden and her team in Brazil say they are now seeing limb joint problems in newborn babies that might be caused by Zika too.
The seven babies with suspected Zika infection that they studied in hospital had been born with hip, knee, ankle, elbow, wrist and/or finger joint problems that fit with a medical diagnosis called arthrogryposis.
The deformities of arthrogryposis, or crooked joints, are caused by faulty muscles – some too tight or contracted and some too flaccid – that have pulled and held the baby’s growing body in unnatural positions.
Dr Linden’s team suspect the Zika virus attacks brain nerve centres supplying the muscles around the joints, rather than the joints themselves. Scans of the babies’ brains appear to support this idea.
All of the seven babies they examined tested negative for other congenital (pre-birth) infections, such as rubella and HIV, that might have been a possible cause of their deformities. Most had microcephaly as well as the limb deformities.
Dr Linden says that, since writing up her findings, she has seen 14 more babies with similar problems and is running more tests.
Prof Jimmy Whitworth, from the London School of Hygiene and Tropical Medicine, said that while not concrete proof, the evidence that Zika might be to blame was “pretty compelling”.
He said the challenge was stopping the spread of the infection and caring for those who will be affected in the long as well as the short term.
“Studies suggest the current epidemic could go on for three or four years,” Prof Whitworth said.
“We think there’s going to be tens of thousands of babies who could be affected by Zika.
“Meeting their physical and psychosocial needs will be the real challenge.”