New Study Explains Why Flu Virus Forms Filaments

Influenza A virus particles strategically modify their shape becoming either spheres or larger filaments to enhance their ability to infect cells based on environmental conditions, according to a new study conducted by scientists at the National Institutes of Health (NIH).

This previously unrecognized adaptive response may help explain how influenza A and other viruses persist in populations, evade immune defenses, and acquire adaptive mutations, as detailed by the researchers in a study published in Nature Microbiology.

The study, led by intramural researchers at the NIH’s National Institute of Allergy and Infectious Diseases (NIAID), aimed to uncover why many influenza A virus particles take on a filamentous shape.

The researchers noted that forming the filament shape requires more energy than forming a sphere and its prevalence had not been fully understood. To investigate, they developed a method to observe and measure the real-time structure of influenza A virus particles during their formation.

The researchers discovered the following:

• Influenza A viruses rapidly alter their shape when exposed to conditions that reduce infection efficiency, such as the presence of antiviral antibodies or host incompatibility.
• A virus’s shape is dynamic and influenced by its environment, rather than being fixed by its strain, as was previously assumed.
• The study examined 16 different virus-cell combinations, which revealed predictable trends in shape adaptation.

Earlier experiments by the team demonstrated that influenza A virus filaments can resist inactivation by antibodies. The researchers are now working to understand precisely how antibodies influence viral shape and infection efficiency.

They also aim to investigate how viral mutations impact the virus’s shape. Additionally, the researchers note that many other viruses such as measles, Ebola, Nipah, Hendra, and respiratory syncytial virus employ a similar mixed-shape infection strategy.