The mosquito-born Zika virus may be responsible for an excess number of birth defects in U.S. states and territories where the virus had been circulating in local mosquito populations, even in women who had no lab evidence of Zika exposure during pregnancy, U.S. health officials said on Thursday.
Areas with local Zika transmission, including southern Florida, a portion of south Texas and Puerto Rico, saw a 21 per cent increase in birth defects strongly linked with Zika during the last half of 2016 — when Zika was present — compared with the first half of that year, the U.S. Centers for Disease Control and Prevention reported.
Researchers said it is not clear whether the increase is due to local transmission of Zika alone, or other contributing factors.
The Zika outbreak was first detected in Brazil in 2015 and quickly spread through the Americas. It has been linked to thousands of suspected cases of microcephaly, a typically rare birth defect marked by unusually small head size, as well as eye abnormalities and nerve damage resulting in joint problems and deafness.
For the study, the CDC looked at nearly one million births in 15 U.S. jurisdictions in 2016 to find birth defects possibly associated with Zika.
They broke these states and territories down into three groups — places with local Zika transmission, places with higher levels of travel-associated Zika, and places with lower rates of travel related Zika.
The researchers found about three out of every 1,000 babies born in the jurisdictions under study had a birth defect that could have been associated with Zika virus infection in the mother.
About half of those babies were born with brain abnormalities and/or small head size.
Because many pregnant women exposed to Zika virus in late 2016 gave birth in 2017, CDC researchers anticipate that there could be another increase in possible Zika-related birth defects when 2017 data are analyzed.
“Babies with Zika-related birth defects need all the help they can get, as soon as possible and for as long as they need it,” said CDC Director Dr. Brenda Fitzgerald in a statement. “This report highlights the critical importance of documenting birth defects possibly related to Zika and our need to maintain vigilance.”
The CDC uses the U.S. Zika pregnancy and infant registry to track pregnancies with laboratory evidence of Zika infection, and a surveillance system to track any birth defects that could possibly be related to the virus.
Zika virus in Canada
According to information posted on the Public Health Agency of Canada’s website, there have been 37 cases of Zika virus reported among pregnant women in Canada as of Dec. 1, 2017 — the latest data available.
There have been two reports of babies born in Canada with “Zika-related anomalies,” the website said.
However, the agency notes that “pregnancy outcomes for Zika-infected women are not generally known” in Canada.