For more than 50 years, it has been supposed that the rate of spread of viruses is limited by replication kinetics in an iterative process of infection, replication and release, but scientists at Imperial College London have now challenged this view. Using live video microscopy, vaccinia virus was found to spread four times more quickly than should have been possible, based on the rate at which it can replicate. The videos showed that the virus spreads by surfing from cell to cell, using a mechanism that allows it to bounce past cells that are already infected and reach uninfected cells as quickly as possible. Soon after vaccinia infects a cell, two viral proteins, A33 and A36, are expressed at the cell surface, marking the cell as infected. When new viruses approach the infected cell, these proteins trigger the host cell to project actin ‘tails’ which physically repel approaching viruses. In this way, the viruses are propelled from cell to cell until they find one that is not already infected.
HSV-1 also spreads at a faster rate than should be possible given its replication rate and may use a similar spreading mechanism. If the ability to signal that a cell is already infected proves to be a common feature of pathogenic viruses, the discovery could eventually lead to new antiviral drugs that exploit this mechanism.
The study is published in the journal Science.