Medical researchers, for the first time, have established that two common respiratory viruses can fuse to form a hybrid virus capable of evading the human immune system, and infecting lung cells.
Experts believe the findings could help to explain “why co-infections can lead to significantly worse disease for some patients, including hard-to-treat viral pneumonia”.
Data shows that each year, around five million people around the world are hospitalised with influenza A, while respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections in children under five years old and can cause severe illness in some children and older adults.
“Respiratory viruses exist as part of a community of many viruses that all target the same region of the body, like an ecological niche,” said Dr Joanne Haney from the MRC-University of Glasgow centre for virus research, who led the study.
“We need to understand how these infections occur within the context of one another to gain a fuller 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, rather than competing with one another as some other viruses are known to do, they fused together to form a palm tree-shaped hybrid virus – with RSV forming the trunk, and influenza the leaves.
“This kind of hybrid virus has never been described before,” said Prof 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 the external proteins of both viruses. It is a new type of virus pathogen.”
The Guardian reports that: Once formed, the hybrid virus was also able to infect neighboring cells – even in the presence of antibodies against influenza that would usually block infection. Although the antibodies still stuck to influenza proteins on the hybrid virus’s surface, the virus merely used neighboring RSV proteins to infect lung cells instead. Murcia said: “Influenza is using hybrid viral particles as a Trojan horse.”