The evolutionary path of a virus can help scientists predict whether it may be the next swine flu virus, Yale researchers have found.

Post-doctoral fellow Nadya Morales, who works in Ecology and Evolutionary Biology professor Paul Turner’s lab, has shown that viruses that have evolved to infect multiple hosts are more likely to shift hosts. Her research findings, currently in review, may be used to prepare for epidemics like swine flu and avian flu by creating vaccines before the virus infects humans, Morales said.

“From this experiment, we have direct evidence for what scientists have suspected about the success of emerging pathogens,” Turner said.

Previously, scientists had little evidence to prove that viruses that can infect multiple hosts would be more able to infect new hosts, Turner said. Since swine flu and avian flu were caused by RNA viruses, which are known for high mutation rates, Morales used laboratory-created strains of a certain RNA virus carried by insects as a model to test this theory. When introduced to new host cells, specialized strains that were grown on either only human cancer cells or only dog cells grew less than a generalized strain that grew alternately on both species.

“The experiment supports the idea that generalists would do better in a new environment,” Morales said.

Though Morales used viral growth as the criteria to determine success, there may be other characteristics that can predict potential host-shifting viruses, Turner said. Whether a virus can survive outside of an old host before finding a new one may also be important — a factor that another post-doctoral fellow in Turner’s lab, Brandon Ogbunugafor, tested.

Ogbunugafor compared specialized and generalized viral strains by dividing the viral life cycle into three components. While generalized viral strains could infect a host, make copies of itself and get out of the host cells equally well, specialized viral strains showed more variance.

“There’ll be tradeoffs,” Ogbunugafor said. “The [generalists] won’t be good at everything, but they’ll be good enough.”

And good enough, Turner said, is all a virus really needs to survive in new environments.

“Even if a virus grows poorly inside a host, it may still be better able to infect it,” Turner said.

Other RNA viruses include the yellow fever virus, rabies virus and the measles virus.