Two common respiratory viruses can fuse to form a hybrid virus that can elude a person’s immune system and infect lung cells.
This is the first time such a viral collaboration has been observed. The researchers believe the findings may help explain why co-infections cause marked deterioration in some patients, including hard-to-treat viral pneumonia.
About 5 million people worldwide are hospitalized each year with influenza A, with respiratory syncytial virus (RSV) being the leading cause of acute lower respiratory infection in children under five and can cause severe illness in some children and the elderly.
While coinfection, where a person is infected with both viruses at the same time, is considered relatively common, it was not clear how these viruses would react if they were in the same cell.
Dr Joan Haney of the University of Glasgow Center for Virological Research, who led the study, said: “Respiratory viruses exist as part of a community of many viruses that target the same area of the body, such as a niche. We need to understand how these infections occur in some regions, in the context of others, to get a better picture of the biology of each individual virus.”
To investigate, Dr. Guang and her colleagues deliberately infected human lung cells with both viruses and found that instead of competing with each other, as some other viruses do, the two viruses fuse together to form a palm-shaped hybrid virus. with respiratory syncytial virus formation on the stem and influenza on the leaves.
Professor Pablo Murcia, who led the study published in the journal Nature Microbiology, explained: “This type of hybrid virus has not been described before. We are talking about viruses from two completely different families that merge together with the genomes and external proteins of both viruses. This is a new type of virus agent.”
Once formed, the hybrid virus was also able to infect neighboring cells – even in the presence of anti-flu antibodies that would normally prevent infection. Although the antibodies were still attached to influenza proteins on the surface of the hybrid virus, the virus instead used neighboring respiratory syncytial virus (RSV) proteins to infect lung cells.
“Influenza uses hybrid virus particles as a Trojan horse,” Murcia notes.
In addition to helping viruses evade the immune system, the combined powers may also allow them to reach a wider range of lung cells.
While the flu typically attacks cells in the nose, throat, and trachea, respiratory syncytial virus tends to favor cells in the trachea and lungs, although there is some overlap.
This potentially increases the chance that the flu will cause a severe and sometimes fatal lung infection called viral pneumonia, said Dr Stephen Griffin, a virologist at the University of Leeds.
However, he cautioned that more research is needed to prove that hybrid viruses are linked to human disease. “Respiratory syncytial viruses tend to get into the lungs compared to the seasonal flu virus, and you’re more likely to get more severely ill the farther away the infection is,” Griffin added. “That’s another reason to avoid getting multiple viruses because such hybridization can occur if we do not take the precautions necessary to protect our health.
Remarkably, the team showed that hybrid viruses can infect cultured cell layers as well as individual respiratory cells.
The next step is to confirm whether hybrid viruses can form in co-infected patients. “We need to know if this only happens with influenza and respiratory syncytial virus or if it spreads to other groups of viruses as well,” Murcia said. “I think yes. And I believe this extends to animal viruses as well. And this is just the beginning of what I think will be a long study, and I hope we have very interesting discoveries ahead of us.”