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April 22, 2016

Using two different Asian strains into which they inserted the E1-A226V mutation, they systematically added additional genetic portions from the African strain, followed by specific mutations to determine which interacted with E1-A226V. Then they tested each change to see whether it affected Aedes albopictus infectivity.

Ultimately, they found that a single genetic element - which also changed an amino acid in the same envelope protein altered by the E1-A226V mutation - increased the Asian chikungunya strains' ability to infect Aedes albopictus by a hundredfold.

"This old Asian lineage needs an additional mutation to adapt to Aedes albopictus, and we think that's what protected India and Southeast Asia from much larger epidemics over the last 60 years," Weaver said. "But some African strains only needed one mutation to spark much larger outbreaks. And now, a strain that emerged from Africa in 2004 seems to be displacing the old Asian strains wherever it goes."

The chikungunya story, Weaver said, demonstrates how small genetic differences among viruses can have dramatic and unexpected effects on their ability to cause human disease. This study also will allow researchers to predict the amount of disease chikungunya may cause if it becomes endemic in the Americas.

"We don't really have the ability to predict when these viruses are going to suddenly mutate and change from one host to another. We can figure out how it happened retrospectively, but we have no idea how many near misses there are," Weaver said. "This was an opportunity to understand one situation where for a long time epidemic emergence didn't happen for a virus in Asia, and how it did happen suddenly when another strain got loose from Africa and started spreading around the globe."

Source: University of Texas Medical Branch at Galveston