By: T.V. Padma
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[NEW DELHI] Scientists have reported subtle genetic changes in the dominant dengue virus strain in southern India – information that has been lacking so far and could be crucial to understanding disease severity.
Dengue, spread by mosquitoes, is prevalent in tropical countries, affecting 100 million people each year. A sharp rise in incidence and severity in recent years has been attributed to increased air travel, urbanisation, deteriorating public health infrastructure and changing climate.
Of the four strains of the dengue virus, the third one (‘DENV 3’) has dominated recent outbreaks in the Indian sub-continent. The genetic material of viruses belonging to each strain is not 100 per cent identical and minor variations can be traced to a common ancestor or ‘lineage’.
Minor changes in the genetic material from one lineage can result in resemblance to viruses from another lineage and such ‘lineage shifts’ are linked to "dramatic increases" in dengue severity in many parts of the world, say researchers in the Virology Journal published on 29 January.
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The researchers, from the southern Indian state of Kerala where dengue re-emerged as an epidemic in 2003 leading to numerous deaths, studied samples of the third strain collected from over 700 patients in the state, between 2008 and 2011. They compared the data with other Indian and global studies and reported a lineage shift (from lineage III to lineage IV) for the first time.
Lineage shift is reflected in changes to virus functions, such as increased or decreased virus multiplication. This, in turn, affects the spread of the virus or the number of people infected during an outbreak, Easwaran Sreekumar, from the viral disease biology programme at the Rajiv Gandhi Centre for Biotechnology (RGCB), Thiruvananthapuram, and one of the authors of the paper, explained to SciDev.Net.
Genetic changes in the virus could also lead to increased or decreased severity of infection, depending on the number of changes that help the virus multiply, Sreekumar said.
"An initial assessment of the cases we studied indicates that they were mild cases with no significant changes in clinical presentation. However, we need to wait and observe how the disease situation progresses in the region in the coming years, along with close monitoring of the viral strains," he added.
S. Swaminathan, staff research scientist at the recombinant gene products group at the International Centre for Genetic Engineering and Biotechnology, New Delhi, says the RGCB team has identified subtle genetic sequence changes that map to a specific region of the protein envelope surrounding the genetic material of the virus.
Swaminathan said the lineage shift may have a bearing on the severity of future dengue cases in Kerala. The RGCB study, he said, would be a step towards understanding the implications of the lineage shift, such as whether the new lineage causes more severe disease or is transmitted more by dengue mosquitoes.
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