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[NEW DELHI] Scientists who discovered a deadly strain of chikungunya virus in India also found that the virus can spread from mosquito to mosquito, bypassing the human transmission stage. This could lead to longer-lasting outbreaks affecting more people.

Scientists at the Rajiv Gandhi Centre for Biotechnology (RGCB) in Thiruvanathapuram, Kerala said this highlighted the need for stricter surveillance and mosquito control measures.

Chikungunya virus, spread mainly by Aedes albopictus mosquitoes and Aedes aegypti that also spread the dengue virus, has caused severe outbreaks across Asia, Africa and Latin America during this decade. Typical symptoms include fever, headache, severe joint pain and nausea.

The scientists analysed a pool of new, short-lived virus strains recorded during a chikungunya outbreak in 2009 in the southern state of Kerala.

They reported in the Virology Journal last month (13 August) that some strains carried the A226V mutation first recorded in the Indian Ocean Island of Reunion during an unprecedented outbreak in 2005-2006 when some 26,000 cases were registered — almost a third of the Island’s population. The infection, previously considered non-fatal, also led to abnormally high death rates during that outbreak.

The re-emergence of chikungunya virus in Reunion puzzled scientists as it was not spread by the usual Aedes aegypti mosquito, but by another mosquito Aedes alpictus that is also common in Asia.

In 2007 scientists reported that a single genetic change, the A226V mutation, altered one of the virus envelope proteins E1, which help the virus enter mammals, including humans, and also adapt to new mosquitoes.

Now, RGCB researcher Easwaran Sreekumar and his team have identified a strain with a mutation in a second envelope protein E2, which helps the virus enter mosquitoes. They also found that the virus can transmit from mother to daughter mosquitoes, bypassing the human transmission stage, which makes it spread quickly through the mosquito population, potentially causing bigger outbreaks.

"It does not need a fresh human host and so can persist for a longer time in a community," Sreekumar said.

If other studies confirm this finding, "we can anticipate persistence of Chikungunya in the community for a longer time till a very large proportion of the people get infected and develop immunity," he added.

Persistence will also enable the virus to accumulate more genetic changes, leading to a more virulent version. "In such situations, as we have now in India, it is essential that we regularly monitor the emergence of new mutant lineages that might have altered characters," Sreekumar said.

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