A new study published in the Feb 1 issue of Plos One suggests that pregnant women infected with respiratory syncytial virus (RSV) can transmit the bug from their respiratory tract to the lungs of their unborn baby – resulting in altered immunity development after birth.

In the study, led by Dr Giovanni Piedimonte of Cleveland Clinic Children’s, pregnant rats were inoculated with RSV. The RSV genome was subsequently found in 30% of fetuses, 40% of newborn rats, and 25% of rats born to infected mothers when tested in adulthood (10 weeks after birth).

RSV is the major cause of infections of the breathing passages and lungs in infants and young children. In addition to causing pneumonia, it is the leading cause of bronchiolitis, an inflammatory disease of the small breathing tubes of the lungs. These two conditions are serious and can become life-threatening.

“Until now we believed that when a pregnant woman got a cold, the developing fetus was protected by the placenta from RSV and other respiratory viruses,” says Dr Piedimonte. “This research is important because it now suggests that respiratory viruses can be transmitted in utero similarly to the Zika virus.”