Washington (AFP)
Fetuses are rarely infected with the new coronavirus because the placenta is said to produce very small amounts of the receptor that the virus uses to enter human cells, concludes a study in the United States.
A baby was born in France in March after being infected during pregnancy, according to a study published in the journal Nature on Tuesday, the first contagion of this type according to the doctors who followed the mother. The baby had neurological symptoms that have been linked to Covid-19 in adults, but recovered within three weeks. In Italy, researchers studying around 30 infected mothers found traces of the virus in a placenta, umbilical cord, mother's vagina and breast milk, but no babies were born positive for SARS-CoV-2 .
The new study, conducted under the aegis of the National Institutes of Health (NIH) and published in the journal eLife Tuesday, is based on the sequencing of genetic material taken from the placenta, the organ that connects the baby to its mother, and the membranes that contain amniotic fluid.
These cells did not have the genetic instructions to make the receptor called ACE2, which is found elsewhere in the body, and which has been identified as the gateway for the coronavirus, particularly in the lungs or the digestive system.
"The molecules necessary for cells to be susceptible to SARS-CoV-2 are rarely expressed in the placenta," said lead author Roberto Romero at AFP.
Conversely, scientists have verified that the genetic instructions necessary for the creation of receptors used by the Zika virus or cytomegaloviruses are abundantly present.
"It proves that our experiences make sense," adds Roberto Romero.
This work would help explain why so-called "vertical" transmission from mother to baby is so rare, in the order of 2% of pregnancies where the mother is infected. For these babies, the researchers write that the virus may be using another gateway, with molecules other than the ACE2 receptor, but we still don't know which ones.
© 2020 AFP