The chikungunya virus circulating in parts of India as well as Sri Lanka and South-East Asia could gain the ability to spread more efficiently by combining mutations, becoming ‘super-adapted’ for transmission by the Asian tiger mosquito, Aedes albopictus, according to research published recently.

Novel form

The virus has been primarily transmitted by the Aedes aegypti mosquito. However, ten years back, a novel form of the virus emerged in coastal Kenya, which then spread to countries around the Indian Ocean, including India, causing huge outbreaks.

Strains of this virus found in islands off Africa, states in India such as Kerala, Sri Lanka and in countries in South-East Asia had a mutation that allowed it to be passed on by the A. albopictus mosquito as well. The mutation changed the virus’ E1 protein.

Subsequently, an additional mutation was discovered in a virus isolated in Kerala in 2009 and from Orissa a year later that altered the viral E2 protein.

The mutation, known as ‘E2-L210Q,’ further enhanced the virus’ ability to replicate in the A. albopictus mosquito and thereby increase its circulation among humans.

A team of scientists led by Scott C. Weaver of the University of Texas Medical Branch at Galveston in the U.S. has identified more E2 mutations, each of which, along with the change in the E1 protein, made the virus more efficient in establishing itself in A. albopictus.

One of these mutations, ‘E2-K252Q,’ first turned up in a virus isolated in Kerala in 2007 and later in viruses from South-East Asia.

More ominously, their paper published recently in Nature Communications alsoprovided experimental evidence that a ‘super-adapted’ form of the virus could potentially emerge by combining E2 mutations.

A lab-created virus with both the E2-L210Q and E2-K252Q mutations was far more effective than either one of those mutations at colonising A. albopictus.

The findings indicated that even more efficient chikungunya virus transmission by A. albopictus “will likely evolve when combinations of these second-step mutations occur in their current ranges of endemic circulation in India and Southeast Asia, followed by their likely global spread,” the scientists noted in the paper.

Although the E2-K252Q mutation has continued to turn up in chikungunya viruses isolated in Kerala, the E2-L210Q had not been seen since 2009, remarked Easwaran Sreekumar of the Rajiv Gandhi Centre for Biotechnology in Thiruvananthapuram, a co-author of the Nature Communications paper. “Fortunately, the two mutations do not currently appear to be co-circulating.” However, regular and systematic surveillance was needed to check for changes in the virus, he pointed out.

Rising immunity

Should a super-adapted strain arise, rising levels of immunity to chikungunya in regions where it is endemic might prevent an increase in disease incidence in the local population, said Dr. Weaver in an email. “I think it is important to do comprehensive surveillance to monitor both CHIKV [chikungunya virus] evolution and rates of herd immunity and disease incidence.”

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