Herpes viruses hedge their bets: latency boosts survival

Herpes viruses have two infectious phases: one just after infecting a new host, and one years or decades later when they reactivate.

According Michael Stumpf (UCL), Zoe Laidlaw (University of Sheffield), and Vincent Jansen (Royal Holloway, University of London), that latency period evolved because it allows the viruses to flourish when the availability of hosts from year to year is highly unpredictable.

Until now, scientists have thought that viruses like herpes simplex 1 and 2, Epstein-Barr virus, and varicella zoster virus, which causes chickenpox and shingles, had evolved latency periods in order to allow them to survive in small host populations.

The new research offers an alternative explanation: the viruses are hedging their bets against the possibility that a sudden outbreak immunises a large part of the population thus drastically reducing the pool of potential hosts. Even in large populations this makes the world very unpredictable from the point view of the virus. The researchers used a mathematical model of how the virus spreads through host populations to determine whether viruses with latency periods could out-compete viruses without latency periods. They found that viruses with latency periods had an evolutionary advantage when the availability of hosts was unpredictable: generally the more unpredictable the environment the more important latency became.

Such dynamics are not limited to viruses: there are many situations, for example portfolio and fund management where a balance between action and patience has to be struck. The present piece of research suggests that successful strategies may often be embarassingly simple: be patient and save something to see you through leaner years.