Two common respiratory viruses can join together to form a hybrid virus capable of evading the human immune system and infecting lung cells – the first time such a viral collaboration has ever been observed.
The researchers believe the findings could help explain why coinfections can lead to significantly worse disease in some patients, including hard-to-treat viral pneumonia.
Each year, about 5 million people worldwide are hospitalized with influenza A, while respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections in children under five years of age and can cause severe illness in some children and older adults. grown ups.
Although co-infections – where a person is infected with both viruses at the same time – are thought to be relatively common, it was not clear how these viruses would react if they were in the same cell.
“Respiratory viruses exist as part of a community of many viruses that target the same region of the body, like an ecological niche,” said Dr Joan Haney of the University of Glasgow’s MRC Center for Viral Research, who led the study.
“We need to understand how these infections occur in the context of each other to get a more complete picture of the biology of each individual virus.”
To investigate, Haney and her colleagues deliberately infected human lung cells with both viruses and found that instead of competing with each other, as some other viruses are known to do, they joined together to form a palm-shaped hybrid virus. tree – where RSV forms the trunk, and influenza forms the leaves.
“This type of hybrid virus has never been described before,” said Professor Pablo Murcia, who supervised the research, published in Nature Microbiology. “We are talking about viruses from two completely different families combining together with the genomes and external proteins of both viruses.” It’s a new type of viral pathogen.”
Once formed, the hybrid virus was also able to infect neighboring cells—even in the presence of flu antibodies that would normally block infection. Although antibodies still stuck to flu proteins on the surface of the hybrid virus, the virus instead used neighboring RSV proteins to infect lung cells. Murcia said, “Influenza uses hybrid virus particles as a Trojan horse.”
In addition to helping viruses evade the immune system, joining forces may also give them access to a wider range of lung cells. While influenza typically infects cells in the nose, throat, and trachea, RSV tends to prefer cells in the trachea and lungs—although there is some overlap.
Perhaps this could increase the chances of the flu causing a severe and sometimes fatal lung infection called viral pneumonia, said Dr Stephen Griffin, a virologist at the University of Leeds. Although he cautioned that more research is needed to prove that hybrid viruses are involved in human disease. “RSV tends to go lower in the lungs than the seasonal flu virus, and you’re more likely to get more severe disease the further down the infection goes,” he said.
“That’s another reason to avoid getting infected with multiple viruses, because this [hybridisation] more are likely to happen if we don’t take precautions to protect our health.”
Significantly, the team showed that the hybrid viruses could infect cultured cell layers as well as single respiratory cells. “This is important because the cells are stuck to each other in an authentic way, and the virus particles will have to go in and out in the right way,” Griffin said.
The next step is to confirm whether hybrid viruses can form in patients with co-infections, and if so, which ones. “We need to know if this only happens with influenza and RSV, or if it also applies to other combinations of viruses,” Murcia said. “My guess is that it is.” And, I guess that extends to animals as well [viruses] Too. This is just the beginning of what I think will be a long journey, hopefully with very interesting discoveries.”