Outsmarted by Viruses? New Research Suggests...
...that this is indeed the case.
Viruses inspire terror in some, even a fear of extinction. Take the HIV virus that causes AIDS, for example, which created quite a panic in the 80’s and 90’s. HIV is one of the fastest evolving entities, introducing changes to its genome with every cycle of replication.
Sloppy, or clever?
For years the cause of AIDS baffled scientists, until finally, a combination therapy seemed to provide a sense of relief. (How to Survive a Plague, a documentary on HIV AIDS, records the efforts made to find a cure from the perspective of an activist group.)
The panic inspired by HIV in the 80’s was reminiscent for many of 1918, a year that saw one of the more violent flu seasons in human history. Taubenberger and Morens write that an estimated 1/3 of the world’s population was infected during that year’s pandemic, and total death tolls were estimated to be around 50 million; in fact, more people died of the flu than in the whole of World War I.
Survival of the Fittest
The statistics are shocking, terrifying. Viruses have the magnificent, even awe-inspiring for some, ability to evolve extremely rapidly.
“They can double their population size in hours, and as a result, host-parasite interactions are rarely one-on-one,” says Helen Leggett, a post-graduate student at Oxford and author on a paper published recently in Current Biology that sought to uncover the viral strategies that evolved in response to “mixed infections”.
“Coinfections result in within-host competition between infecting strains, and [this] can select for a wide range of virus/ parasite strategies that have consequences for how harmful an infection is to the host.”
Leggett said that coinfections are likely to be common in natural environments, and theory suggests that alternating conditions (for example, between a single infection and a coinfection) are likely to lead to the ability of the organism to switch their behavior to “best suit the environmental setting”, or rather, to out-compete the intruder.
In other words, survival of the fittest.
While these changing behaviors have been observed, the evolution of the strategy has not been documented.
The researchers grew up viruses in mixed infection conditions for six months, and observed their behavior by a number of parameters, all to see how they had adapted to living with a roommate.
In short, the viruses evolved the ability to switch their behavior from scratch. “When in mixed infections, the viruses switched their growth to kill hosts more rapidly. This allows them to dominate over other infecting viruses, since the other virus strains were not fully developed when the host cell burst.”
“The viruses only did so when in mixed infections”, said Legget. “Being able to detect the presence of a coinfecting strain and alter their behavior accordingly means that the virus has high fitness under both single and coinfection conditions – a “win-win” strategy!”
It’s likely that this ability has been bestowed upon many viruses, and there are implications for disease control – if viruses can alter their behavior so rapidly, then they are likely to evolve to overcome control measures.
That’s not news.
Can these findings help eradicate the flu? “Probably not,” said Legget. “Our results suggest that we’d need to infect people with more flu viruses in order to change its behavior, and this isn’t really possible.”
Still, the findings are important, proving that viruses can quickly evolve to maximize their spread, and this ought to impact our approach to disease control.