Zika virus now linked to hearing loss in babies, study finds
Doctors are now adding hearing loss to the growing list of health problems linked to Zika infections in babies.
The virus is already known to cause microcephaly, a condition in which babies are born with abnormally small heads and incomplete brain development, among other serious health problems.
In a study of 69 Zika-infected babies with severe microcephaly, about 6 per cent showed hearing loss, according to a study from Centres for Disease Control and Prevention released on Thursday.
The babies were born between November and May and were treated at the Hospital Agamenon Magalhaes in Recife, Brazil, the city at the epicentre of the Zika outbreak in that country.
A number of other viruses are known to cause hearing loss in babies infected prenatally. These viruses include rubella, also known as German measles; genital herpes; syphilis; and cytomegalovirus, a type of herpes virus. Each of these can also cause microcephaly.
“If the hearing loss caused by Zika follows the same pattern seen in these other viral infections, the hearing loss will be permanent,” said James Bale, Jnr, professor of paediatric neurology at the University of Utah School of Medicine, who was not involved in the study.
“Children will need a range of services, including hearing and speech therapy, hearing aids and cochlear implants, surgically implanted devices can help to provide a sense of sound to a person who is profoundly deaf or severely hard-of-hearing.”
Authors of the new study say babies with suspected Zika exposure should undergo hearing tests, even if their hearing screenings at birth appear normal. That’s because other viruses known to cause hearing loss in babies can be delayed, with hearing loss getting worse over time.
“Zika infections rarely harm adults, causing no symptoms in 80 per cent of those infected. The other 20 per cent of people who are infected develop mild symptoms, such as fever, a rash, headache, aches and pains and pink eye, lasting about a week and going away without any treatment,” said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
In rare cases, Zika can cause neurological problems in adults, including Guillain-Barre syndrome, in which the immune system attacks the nerves of the body, causing paralysis. This syndrome can be caused by many viruses, including the flu.
Zika generally doesn’t affect mature brain cells, such as those found in children and adults. But studies show the virus clearly hones in on developing brain cells, such as those in the fetus, Fauci said. In the new Brazilian studies, all of the babies developed a type of hearing loss caused by nerve damage.
Yet the news about Zika’s effects on babies grows worse with nearly every new study. Fauci notes that the full spectrum of Zika’s effects on children may become apparent only in coming years, as children mature.
“Microcephaly may be just the tip of the iceberg,” Fauci said.
Researchers in recent months have documented the catastrophic brain damage suffered by some infants infected with Zika in the womb. Babies with prenatal Zika infections also have been diagnosed with severe joint deformities and vision loss.
Zika appears to be most destruction in early pregnancy, when the fetal brain is undergoing tremendous growth, Fauci said. A study released last week, however, showed that even babies infected in late pregnancy can suffer serious problems.
In that case, a baby boy was infected in the 26th week of pregnancy. A typical pregnancy lasts 40 weeks. The baby appeared healthy at birth, although his head was very small. By the time he was 6 months old, however, he had developed very tight muscles and was paralysed on one side of his body.