Why is the coronavirus passes rarely from the mother to the fetus

Pourquoi le coronavirus passe rarement de la mère au fœtus

Fetuses are rarely infected by the new coronavirus, as the placenta would produce very low amounts of the receptor that the virus uses to enter human cells, concludes a study conducted in the United States.

A baby is born in France in march after having been infected during pregnancy, according to a study published in the journal Nature on Tuesday, the first contagion of this type according to the physicians who have followed the mother. The baby had neurological symptoms that were related to the Covid-19 in adults, but it is restored in three weeks. In Italy, researchers studying a thirty-infected mothers had found any trace of the virus in a placenta, umbilical cord, vagina of a mother and in breast milk, but no baby was born positive for the SARS-CoV-2.

The new study, conducted under the auspices of the national Institutes of health (NIH) and published in the journal eLife on Tuesday, is based on the sequencing of genetic material collected in the placenta, the organ that connects the baby to its mother, and the membranes that contain the amniotic fluid.

These cells did not have the genetic instructions for making the receptor, called ACE2, is found elsewhere in the body, and which has been identified as the door of entry of the coronavirus, including in the lungs or the digestive system.

“The molecules needed for the cells are likely to be infected with SARS-CoV-2 is rarely expressed in the placenta,” says lead author Roberto Romero, AFP.

Conversely, the scientists verified that the genetic instructions necessary for the creation of receptors used by the virus Zika where cytomegalovirus were abundantly present.

“This proves that our experiences have meaning “, adds Roberto Romero.

This work would help to explain why the transmission of so-called “vertical” (from mother to baby, is also rare, of the order of 2 % of pregnancies where the mother is infected. For these babies, the researchers write that the virus may be using a different entrance door, with other molecules that the receptor ACE2, but it is not yet known which.

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