This is the story of two respiratory viruses that meet in a lung. What are they saying to each other? What’s going on ?
In fact, it all depends on which viruses meet and which came first. In some cases, the viruses will be able to coexist and co-infect the cells of the organism to be colonized. In others, infection from one virus will prevent a second from entering and reproducing.
What explains the mechanisms of interference between viruses? This field of virology studies, still little explored, will benefit this winter from great attention from researchers who will want to know if their hypotheses are confirmed in reality.
So much the better for virologists… So what do we know about the interference between viruses?
From the end of the 1950s, virologists began to take an interest in the struggle of certain viruses to be able to infect an organism. The Russian virologist Marina Voroshilova notably discovered that the poliomyelitis virus struggled to take root when an enterovirus was present in the digestive system. “But afterwards, it fell into oblivion for a few decades… until the pandemic”, says the Dr Guy Boivin, Full Professor in the Department of Microbiology-Immunology and Infectiology of the Faculty of Medicine at Laval University. The last two years marked by the arrival of a new virus, SARS-CoV-2, responsible for COVID-19, have revived interest in interference. In particular to answer a question that many people have asked themselves: is it possible to catch the flu and COVID-19 at the same time?
Exactly. Is it possible to catch the flu and COVID-19 at the same time?
Possibly, yes. But the data suggests it’s not common. Which tends to show, believes the Dr Guy Boivin, that the circulation of influenza and COVID-19 viruses does not follow the same curve. When the circulation of SARS-CoV-2 was very high – for example when the Omicron variant appeared last winter – there was little influenza. And vice versa.
Researchers have already noticed that the course of influenza can be slowed by other viruses: in 2009, France and Sweden saw the peak of H1N1 infection shifted by a few weeks compared to their neighbors, possibly because that these two countries were already under attack from rhinoviruses.
Other viruses, such as respiratory syncytial virus (RSV) and rhinoviruses (which cause the common cold), can coexist better. This week, the National Institute of Public Health of Quebec (INSPQ) estimated that 22% of children hospitalized for a respiratory virus are fighting more than one – they were generally suffering from RSV and a rhinovirus. Only 2% of adults hospitalized for respiratory viruses had co-infections, observed the INSPQ. Data that does not surprise the Dr Bovine. “Co-infection is more common in children than in adults probably for several reasons,” he says. Like the fact that children’s immune systems are less developed and their number of contacts is high.
What could determine the level of virus interference?
When a cell is infected by a virus, it secretes molecules called interferons in defense. The other cells, which are not yet infected, also receive the alarm signal to start producing interferons. But not all viruses cause the same amount of interferon to be secreted — the level is much higher in the case of SARS-CoV-2 and influenza. “And a virus can be more or less sensitive to the action of interferons produced against another virus,” says Dr.r Bovine. For example, a high level of interferons produced to get rid of COVID-19 will keep all other viruses at bay. But as soon as the level goes down and two viruses present themselves—say, influenza and RSV—which one attacks first? “The influenza should take over”, believes the Dr Bovine.
Other viruses will also take advantage of the fact that the body is attacked to attack. “A person who is fighting an infection can have damaged airways,” notes Professor Benoit Barbeau, from the department of biological sciences at UQAM. “It is possible that at this time, certain viruses want to be able to take advantage of this environment. »
The observations that will be made this winter will make it possible to better understand the activity peaks of the viruses and to predict their trajectory. “It’s confusing for hospitals, especially in pediatrics, but it’s interesting from a scientific point of view,” says Dr.r Guy Bovin. I think we will learn a lot during this period. »
Great… But if you prefer not to participate in this virological experiment live ?
There are still good ways to escape respiratory viruses, recalls Benoit Barbeau: the mask and vaccines. “But hey, I know it’s a bit flat to say that we still have to be vigilant…”