Los Alamos National Laboratory

Creating a Hybrid Virus

New strains of influenza A can emerge from genetic reassortment, which happens only when two or more viral strains infect the same host cell.

Seasonal influenza A viruses new strains of Influenza A description

The infection starts when HA proteins on the virus’s surface bind to the cell surface (A). The cell engulfs the virus, trapping it inside an endosome. (B) As discussed in the main text, HA causes a channel to open in the endosome, which lets the viral RNA enter the cell’s interior. (C) Inside the cell nucleus, each RNA segment is copied, while viral proteins are made outside the nucleus. Newly made HA and NA proteins are transported to the cell membrane and protrude from it. Other proteins (not shown) return to the nucleus, where they and the RNA segments self-assemble into new viral cores. (D) The core migrates to the cell surface and gets coated with membrane as it leaves the cell.

The lower half of the figure shows a second virus infecting the cell. (E) The two sets of RNA segments can mix in the nucleus (get reassorted), as represented by the exchange of two HA segments. The result is two hybrid viruses with their own traits and behaviors.

Seasonal influenza A viruses RNA strains description

In this graph, each horizontal line corresponds to one of influenza’s eight RNA segments and groups of eight correspond to a viral subtype. Through reassortments, three subtypes evolved into six. The 2009 H1N1 swine flu virus resulted from a series of reassortments. It contains two RNA segments from H1N1 avian virus, one from H3N2 seasonal human virus, and five from pigs (H1N1 Classical swine virus and the Triple reassortant swine).

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