Bronchiolitis surprises with its precocity

This viral disease circulated very little last year, which could favor a large-scale epidemic.

The bronchiolitis epidemic arrives several weeks in advance on the territory. Île-de-France and the Grand Est have entered an epidemic phase and the other metropolitan regions are in the pre-epidemic phase. “The previous epidemic was declared very late since it was especially rife in the spring of 2021, explains Delphine Viriot, epidemiologist at Public Health France. If we compare with previous years, the level of circulation of the current virus corresponds to that usually observed in early November. ” More than 600 children under the age of 2 were hospitalized after going to the emergency room the week of October 4. The epidemic threshold is declared when more than 10% of emergency treatment in children under 2 years old is linked to the disease.

Bronchiolitis is a seasonal disease caused by respiratory syncytial virus (RSV). It usually appears during fall, peaking around late December and disappearing in spring. “In an infant, it is initially characterized by a cough and possibly a fever, even mild, symptoms not very different from other infections., continues Delphine Viriot. It becomes worrisome when the breathing is rapid and wheezy. Almost 3% of children under the age of 1 are hospitalized for severe forms of bronchiolitis. ” The disease particularly affects very young children, more rarely the elderly or immunocompromised.

Cells called “neonatal regulatory B lymphocytes”, found only in very young children, can be directly infected with RSV. What will inhibit the antiviral immune response

Olivier Schwartz, director of the virus and immunity unit at the Institut Pasteur

Barrier gestures

“The lungs of young children are still immature, in some cases they will have difficulty in evacuating mucous plugs in the bronchioles, explains Olivier Schwartz, director of the virus and immunity unit at the Institut Pasteur. In addition, cells, called “neonatal regulatory B lymphocytes”, present only in very young children.s, can be directly infected with RSV. This will inhibit the antiviral immune response, as a team of immunologists from the Institut Pasteur showed a few years ago. ”

Last year, the virus circulated very little and the epidemic peak was half that of the previous year. In its opinion dated October 5, the Scientific Council was therefore concerned about the risk of a large-scale epidemic. “Competition with Sars-CoV-2, confinements and barrier gestures have made it possible to limit the number of cases, indicates Delphine Viriot. The corollary is that there was less immune stimulation, which may explain this precocity. ” Because, if infants are particularly vulnerable to the disease, the virus spreads throughout the population, where it usually causes only mild colds. Fewer people infected last year means fewer individuals with antibodies and therefore more potential vectors of the disease. “We do not know at all if this rapid departure will shift the peak in time or if more babies will fall ill, note Delphine Viriot. The best way to fight is to insist on prevention tools, which are the same as those against Covid-19: hand washing, social distancing, room ventilation, masks, etc. ” For many scientists, the risk of encountering more virulent epidemics this year than usual is an argument that justifies maintaining certain measures until next spring.

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