The incidence of dengue, a viral disease transmitted by mosquitoes, has increased steadily over the past 50 years, mainly in Southeast Asian countries.

And still have There is no approved dengue vaccine in India, although some vaccines have been developed in other countries.

Severity of Dengue Virus Strains

“We were trying to understand how different the Indian variants were, and we found that they were very different from the original strains used to make the vaccines,” said Rahul Roy, associate professor in the Department of Chemical Engineering (CE), IISc.

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The team checked everything Genetic sequence of available (408) Indian Dengue strains From infected patients collected by others and the team themselves between 1956 and 2018.

There are four broad categories of dengue virus — serotypes (Deng 1, 2, 3 and 4). Using computational analysis, the team examined how much each of these serotypes deviated from its ancestral sequence, from each other, and from other global sequences.

“We found that sequences change in very complex ways,” Roy said.

Until 2012 The dominant strains in India were Dengue 1 and 3. In recent years, Dengue 2 has become more prevalent across the country, while Dengue 4, once considered the least contagious, is now gaining ground in South India, according to researchers.

The team tried to investigate which factors prevailed at any given time.

Understanding Dengue Virus Evolution

One possible factor could be Antibody-Dependent Enhancement (ADE), said Suraj Jagtap, PhD student at CE.

Jagtap explained that sometimes people can be infected with one serotype first and then a secondary infection with a different serotype causes more severe symptoms.

Scientists believe that if the second serotype is similar to the first, antibodies produced in the host’s blood after the first infection combine with the new serotype and bind to immune cells called macrophages.

This proximity allows the newcomer to infect macrophages, making the infection more severe.

“We knew that ADE increased virulence, (but) we wanted to know if it could also change the evolution of the dengue virus,” Jagtap said.

At any one time, several strains each serotype is present in the viral population. Antibodies produced in the human body after primary infection provide complete protection against all serotypes for about 2-3 years. Over time, antibody levels begin to drop, and cross-serotype protection is lost.

Fighting Dengue

The researchers suggest that if the body is infected with a similar—not identical—strain of the virus around this time, ADE kicks in and gives this new strain a strong advantage, causing it to become the dominant strain in the population.

Such an advantage continues for several more years, after that antibody levels are very low to make a difference.

“That’s what’s new in this paper,” Roy said. “Nobody has shown such a correlation between dengue virus and human population immunity.”

That’s probably why The latest Dengue 4 strains replacing Dengue 1 and 3 strains, According to the researchers, they were more similar than their ancestral Dengue 4 strains.

Roy explained that such insights are only possible by studying countries like India with genomic surveillance of the disease, where infection rates have historically been high and a large population carries antibodies from a previous infection.

Source: IANS

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