Warning as new hybrid virus threatens to evade immunity

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For the first time, researchers have discovered a new type of hybrid virus pathogen, formed after two viruses fused together. The RSV and influenza viruses, each responsible for tens of thousands of deaths each year, have fused together to form a virus that evades immunity. Through this finding, researchers believe they can understand why co-infections, which is where a person is infected with two viruses at the same time, can lead to a disease becoming significantly worse for some patients, including hard-to-treat viral pneumonia. Influenza A is responsible for about 5 million people around the world being hospitalised every year, while in the UK, over 30,000 babies and children under 5 are hospitalised every year after suffering from respiratory syncytial virus (RSV)

The virus, which can cause serious respiratory infections such as pneumonia and bronchiolitis (inflammation of the airways), 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.

While co-infections are relatively common, researchers were unsure about how these viruses would respond if they found themselves inside the same cell. 

Dr Joanne Haney from the MRC-University of Glasgow centre for virus research, who led the study told the Guardian: “Respiratory viruses exist as part of a community of many viruses that all target the same region of the body, like an ecological niche.

“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.”

In the study, Dr Haney and her colleagues deliberately infected human lung cells with the two virus strains, and discovered that insteading of competing with each other for control of the cell, as some other viruses have been known to do, this pair fused together. 

The two viruses fused to form a palm tree-shaped hybrid pathogen – with RSV forming the trunk, and influenza the leaves. Prof Pablo Murcia, who supervised the research, published in Nature Microbiology said: “This kind of hybrid virus has never been described before.

“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.”

Once the hybrid strain was formed, it was able to infect neighbouring cells, even evading antibodies that would generally block influenza infections.

Although the antibodies would still stick to the influenza proteins present on the pathogen’s surface, this new hybrid virus would use neighbouring RSV proteins to infect lung cells instead. Prof Murcia said: “Influenza is using hybrid viral particles as a Trojan horse.”

Researchers warn that aside from evading the immune system, joining forces could also help these viruses access a wider range of lung cells. While influenza typically infects cells in the nose, throat and windpipe, RSV likes to attack the windpipe and lung cells. 

Dr Stephen Griffin, a virologist at the University of Leeds warned that such hybrid viruses could raise the chances of influenza triggering a much more severe lung infection known as viral pneumonia.

However, he added that more research would be required in order to prove that such viruses are implicated in human disease, saying: “RSV tends to go lower down into the lung than the seasonal flu virus, and you’re more likely to get the more severe disease the further down the infection goes.

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It is another reason to avoid getting infected with multiple viruses because this [hybridisation] is likely to happen all the more if we don’t take precautions to protect our health.”

The researchers also found that the hybrid viruses could infect cultured layers of cells, as well as individual respiratory cells, which Dr Griffin noted is important “because the cells are stuck to one another in an authentic way, and the virus particles will have to go in and out in the right way.”

The team noted that the next step in their research is to confirm whether such hybrid viruses could form in patients with co-infections. 

Prof Murcia said: “We need to know if this happens only with influenza and RSV, or does it extend to other virus combinations as well. My guess is that it does. And, I would hypothesise that it extends to animal [viruses] as well. This is just the start of what I think will be a long journey, of hopefully very interesting discoveries.”

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