Influenza-Common Respiratory Detected First Time, Can Evade Immunity

For the first time, scientists have detected a hybrid virus that can evade the immune system. The influenza A virus and the respiratory syncytial virus (RSV) can fuse together to form a hybrid virus and can infect lung cells. The findings were reported in Nature Microbiology on October 24. 

It is well known that co-infections can be very dangerous at times, causing serious illness. In co-infections, a patient already infected with one pathogen (a disease-causing agent such as a virus, bacteria or fungi, etc.) in infected by another one at the same time. Co-infections are considered to be relatively common, but how exactly two viruses would behave when they are present at the same time in the same cell remained unclear. The new study, as experts say, can shed light on how co-infections can occur and how they can be stopped. 

When our body is encountered with a pathogen, our defence mechanism, or the immune system, comes into action quickly to fight it off. With pathogens evolving newer ways of evading immunity, it is of paramount importance how they behave inside our body—and in case of co-infections, it becomes more important.

Around 5 million people around the world are hospitalised due to infection with influenza A and at the same time, RSV is the leading cause of lower respiratory tract infection, especially among children below the age of five. This virus can also cause severe diseases in children and adults as well. 

Joanne Haney, from MRC-University of Glasgow, who led the Nature Microbiology study, said in a statement, “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.”

To investigate how influenza A and RSV would behave in the same cellular environment at the same time, Haney and her colleagues infected human lung cells with both viruses. They found that instead of competing with each other, the viruses fused together and became one to emerge as a palm tree-shaped hybrid virus.

The influenza virus formed the leaves while the RSV virus formed the trunk of the palm tree-shaped formation of the hybrid. Notably, there are viruses that compete with each other when present in the same environment at the same time. 

Professor Pablo Murcia, the corresponding author of the study, explained, “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.”

The hybrid virus was able to infect neighbouring cells and that too in the presence of antibodies against the influenza virus. Antibodies are specialised proteins that are produced by the immune system and they block the proliferation of a pathogen. In the case of the influenza-RSV hybrid, the antibodies against influenza could stick to the viral proteins. But the hybrid also has the RSV and with the help of it, the hybrid could infect neighbouring lung cells. In a sense, the influenza virus uses the hybrid as a Trojan horse. 

Influenza virus usually prefer to infect the nose, throat and windpipe cells whereas the RSV tends to infect lung and windpipe cells. However, there is some overlap in terms of types of cells that the two viruses tend to infect.

Experts opine that with the hybrid virus in place, influenza can cause a severe lung infection like pneumoniae. The team found that the hybrid virus could infect layers of cells cultured in lab as well as individual respiratory cells.

The researchers plan to explore in future whether hybrids form with other sets of viruses apart from influenza and RSV. Murcia said that hybrid formation is possible with other sets of viruses as well and he hypothesise that it can extend to animal viruses as well. Future researches in this direction will help understand how dangerous co-infections could be and how hybrids can worsen the scenario.