The vaccinia poxvirus spreads infection by jumping from one cell to another before it finds an uninfected cell, according to a new British research.
According to lead researcher Geoffrey Smith of Imperial College London, this 'viral bouncing' is responsible for experiments in which vaccinia spreads much more faster across a dish of cells than viral reproduction rates should allow.
"A virus might hit a cell that's already infected, get bounced away, hit another, get bounced away again ... and eventually it will find a cell that is uninfected, which it can enter...The virus is so smart," Nature quoted Smith, as saying.
To find how the virus hops Smith and his team used live-imaging techniques and fluorescently tagged viruses.
A cell infected by vaccinia rapidly starts producing two viral proteins, called A33 and A36. These proteins form a complex at the cell's outer membrane, which marks the cell as infected. When other vaccinia particles collide into the membrane and try to infect the already-infected cell, the viral particles get stuck to the protein complex. This docking leads the cell to produce a long filament, composed of the building-block protein actin - that thrusts the virus outward.
What this means, according to Smith, is that vaccinia deceives cells into saying: "Hey guys, we're infected already, no point coming in here. You need to go somewhere else."
Smith and colleagues found that crippling the A33 and A36 genes inside vaccinia dampened infection rates significantly, whereas inserting the genes for only these two proteins into human cells - without the rest of the vaccinia genome - was enough to spark off actin-filament propulsion on contact with new virus particles.
The researchers thus concluded that the two proteins are all that is necessary for the exercise.
The study has appeared online in Science1.