Dengue virus has 'evolved dramatically' to be more severe in India: Study

A team of scientists led by the Indian Institute of Science IISc recently said the dengue virus has evolved to be more severe in India while stressing on the need for developing a vaccine against the strains found in the countryIn a multiinstitutional study on dengue published in the journal PLoS Pathogens the scientists showed how the virus causing the disease has evolved dramatically over the last few decades in the Indian subcontinentCases of dengue a mosquitoborne viral disease have steadily increased in the last 50 years predominantly in the SouthEast Asian countriesAnd yet there are no approved vaccines against dengue in India although some vaccines have been developed in other countriesWe were trying to understand how different the Indian variants are and we found that they are very different from the original strains used to develop the vaccines said Rahul Roy associate professor at the Department of Chemical Engineering CE IIScThe team examined all available 408 genetic sequences of Indian dengue strains from infected patients collected between the years 1956 and 2018 by others as well as the team themselvesThere are four broad categories serotypes of the dengue virus Dengue 1 2 3 and 4 Using computational analysis the team examined how much each of these serotypes deviated from their ancestral sequence from each other and from other global sequencesWe found that the sequences are changing in a very complex fashion Roy saidUntil 2012 the dominant strains in India were Dengue 1 and 3 But in recent years Dengue 2 has become more dominant across the country while Dengue 4 once considered the least infectious is now making a niche for itself in South India the researchers foundThe team sought to investigate what factors decide which strain is the dominant one at any given timeOne possible factor could be Antibody Dependent Enhancement ADE said Suraj Jagtap doctoral student at CEJagtap explained that sometimes people might be infected first with one serotype and then develop a secondary infection with a different serotype leading to more severe symptomsScientists believe that if the second serotype is similar to the first the antibodies in the hosts blood generated after the first infection bind to the new serotype and bind to immune cells called macrophagesThis proximity allows the newcomer to infect macrophages making the infection more severeWe knew that ADE enhances severity but we wanted to know if that can also change the evolution of dengue virus Jagtap addedAt any given time several strains of each serotype exist in the viral population The antibodies generated in the human body after a primary infection provide complete protection from all serotypes for about 23 years Over time the antibody levels begin to drop and crossserotype protection is lostThe researchers propose that if the body is infected around this time by a similar not identical viral strain then ADE kicks in giving a huge advantage to this new strain causing it to become the dominant strain in the population Such an advantage lasts for a few more years after which the antibody levels become too low to make a differenceThis is what is new about this paper Roy said Nobody has shown such interdependence between the dengue virus and the immunity of the human population beforeThis is probably why the recent Dengue 4 strains which supplanted the Dengue 1 and 3 strains were more similar to the latter than their own ancestral Dengue 4 strains the researchers believeSuch insights are possible only from studying the disease in countries like India with genomic surveillance explained Roy because the infection rates here have been historically high and a huge population carries antibodies from a previous infectionAlso Read Mumbai experts on why dengue spikes during the monsoonThis story has been sourced from a third party syndicated feed agencies Midday accepts no responsibility or liability for its dependability trustworthiness reliability and data of the text Midday managementmiddaycom reserves the sole right to alter delete or remove without notice the content in its absolute discretion for any reason whatsoever