Washington, May 6 - What causes a dormant virus to go on a sudden rampage, infecting a large number of people? It could be something as simple as a single mutation in an African strain of the chikungunya virus.

A discovery by the University of Texas Medical Branch says the mutation (alteration) was so tiny that a researcher likened it to "a single missing comma in a six-page short story", reports the journal Proceedings of the National Academy of Sciences.

Studying such mutations in different chikungunya strains has helped Texas Medical Branch researchers solve one of the most puzzling mysteries, after the emergence of the virus in Asia.

Chikungunya, which originated in Africa, is carried by mosquitoes and causes intensely painful arthritis that can last for months or years, according to a Texas statement.

But this so-called E1-A226V mutation made it possible for the virus to efficiently infect Aedes albopictus -- a species of mosquito found nearly worldwide.

The mutated strain of the virus took full advantage of its new host, infecting millions of people as it spread across India, Thailand and Malaysia.

It even jumped to northern Italy, carried by an infected traveller, where it established itself in the local Aedes albopictus mosquito population.

"Asia is Aedes albopictus's native territory, but we can't find any evidence of chikungunya transmission by albopictus until the arrival of this new strain," said Texas pathology professor Scott Weaver, co-author of the study.

"It was surprising to us that strains of this apparently very adaptable virus circulated in Asia for 60 years without making the adaptation that would allow them to be transmitted by albopictus."

Weaver and his colleagues used 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 alternation 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 strain's ability to infect Aedes albopictus by a hundredfold. (IANS)