Observed for the first time:Immune system-evading hybrid virus

Researchers found the RSV and influenza viruses fused together to form a new type of virus pathogen!

Two common respiratory viruses can fuse to form a hybrid virus capable of evading the human immune system, and infecting lung cells – the first time such viral cooperation has ever been observed.

Researchers think the findings could help to explain why co-infections can lead to significantly worse disease for some patients, including hard-to-treat viral pneumonia.

The flu virus and respiratory syncytial virus (RSV) can fuse together to create a virus that can evade the human immune system.

Scienitsts 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. It is 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 formed, the hybrid virus was also able to infect neighbouring 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 neighbouring RSV proteins to infect lung cells instead. “Influenza is using hybrid viral particles as a Trojan horse.”

As well as helping the viruses evade the immune system, joining forces may also enable them to access a wider range of lung cells. Whereas influenza usually infects cells in the nose, throat and windpipe, RSV tends to prefer windpipe and lung cells – although there is some overlap.

Possibly, it could increase the chances of influenza triggering a severe, and sometimes fatal, lung infection called viral pneumonia.

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.

Significantly, the research team showed that the hybrid viruses could infect cultured layers of cells, as well as individual respiratory cells.

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 happens only with influenza and RSV, or does it extend to other virus combinations as well. Scientists think that it does. And, they  hypothesise that it extends to animal [viruses] as well. This is just the start of what they think will be a long journey, of hopefully very interesting discoveries.

https://www.nature.com/articles/s41564-022-01242-5