For the first time ever, a pair of common respiratory viruses have been observed fusing to form a hybrid virus. According to new research, influenza A and respiratory syncytial virus (RSV) can combine (in human lung cells at least) to create not one but two never-before-seen hybrid viruses with the potential to evade the immune system.
The findings represent a unique opportunity for virologists to investigate viral coinfection of human cells, which may eventually help them explain why coinfections can result in worse disease outcomes for patients.
However, the research is just in human cells, for now. It remains to be seen whether the same virus hybridization occurs in actual humans infected with the two viruses.
“This kind of hybrid virus has never been described before,” Professor Pablo Murcia, who supervised the research, told The Guardian. “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.”
Influenza A and RSV are both common respiratory viruses known to circulate in the winter months. Influenza A causes influenza in birds and mammals and is responsible for over 5 million hospitalizations worldwide each year. RSV, meanwhile, can cause serious illness in older people and infants and is the leading cause of acute lower respiratory tract infection in children under five.
In the new study, researchers from the University of Glasgow demonstrated what happens when human cells are infected by these two pathogens at the same time – a so-called “coinfection” of the two viruses. Coinfections are relatively common, accounting for up to 30 percent of all respiratory viral infections. However, it is not known how they affect the severity of disease.
“Respiratory viruses exist as part of a community of many viruses that all target the same region of the body, like an ecological niche,” first author Dr Joanne Haney said in a statement. “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.”
Coinfecting human lung cells with both viruses, Haney and co-authors set about investigating this. Using super-resolution microscopy, live-cell imaging, scanning electron microscopy, and cryo-electron tomography, they observed two new hybrid virus particles. These particles contained elements from both influenza A and RSV, including genetic information.
The hybrid viruses were therefore able to evade the immune system. One was found to infect neighboring cells with influenza A by using the RSV proteins on their surface, enabling the virus to continue to infect even when anti-influenza antibodies were present. Utilizing the cell entry mechanism of RSV in this way also allows the hybrid virus to access cells that a regular influenza A virus could not, thus expanding its range of potential targets.
The researchers believe this could help to explain why some people infected with multiple viruses may suffer significantly worse consequences – such as viral pneumonia – than those infected with a single virus.
“Our next steps are to find out if hybrid particles are formed in patients with coinfections, and to identify which virus combinations can generate hybrid particles,” Murcia added in a statement. “Our working assumption is that only few respiratory viruses will form hybrid viruses.”
The study is published in Nature Microbiology.