New Delhi: The dengue virus evolved “dramatically” over the last few decades in India, according to a study led by scientists at the Indian Institute of Science (IISc), which stresses the need for developing a vaccine against the strains found in the country. Dengue cases have steadily increased in the last 50 years, predominantly in the South-East Asian counties. However, there are no approved vaccines against the mosquito-borne viral disease in India, although some vaccines have been developed in other countries. Rahul Roy, Associate Professor at the Department of Chemical Engineering at IISc Bengaluru, said,
We 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.
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The study, published in the journal PLOS Pathogens, 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 themselves. There 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 sequences. Mr. Roy said,
We found that the sequences are changing in a very complex fashion.
Until 2012, the dominant strains in India were Dengue 1 and 3, the researchers said. However, 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, they found.
The team investigated what factors decide which strain is the dominant one at any given time. One possible factor could be Antibody Dependent Enhancement (ADE), said Suraj Jagtap, a PhD student at IISc and first author of the study. ADE occurs when the antibodies generated during an immune response recognise and bind to a pathogen, but they are unable to prevent infection. Instead, these antibodies act as a “Trojan horse,” allowing the pathogen to get into cells and exacerbate the immune response.
Mr. Jagtap 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 symptoms. Scientists believe that if the second serotype is similar to the first, the antibodies in the host’s blood generated after the first infection bind to the new serotype and to immune cells called macrophages.
This proximity allows the newcomer to infect macrophages, making the infection more severe, they said.
We knew that ADE enhances severity, (but) we wanted to know if that can also change the evolution of dengue virus.
The researchers noted that at 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 2–3 years. Over time, the antibody levels begin to drop, and cross-serotype protection is lost, they said.
The 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 difference, they said. Mr. Roy said,
Nobody has shown such interdependence between the dengue virus and the immunity of the human population before.
This 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 said. The reported dengue cases in 2018 have increased more than 25-fold (three year average) since 2002 in India, according to the researchers. All four geographical regions, namely–North, East, South and West-Central India, show periodic spikes in dengue cases as well as deaths over 2–4 years, they added.
(This story has not been edited by NDTV staff and is published from a syndicated feed.)
NDTV – Dettol have been working towards a clean and healthy India since 2014 via the Banega Swachh India initiative, which is helmed by Campaign Ambassador Amitabh Bachchan. The campaign aims to highlight the inter-dependency of humans and the environment, and of humans on one another with the focus on One Health, One Planet, One Future – Leaving No One Behind. It stresses on the need to take care of, and consider, everyone’s health in India – especially vulnerable communities – the LGBTQ population, indigenous people, India’s different tribes, ethnic and linguistic minorities, people with disabilities, migrants, geographically remote populations, gender and sexual minorities. In wake of the current COVID-19 pandemic, the need for WASH (Water, Sanitation and Hygiene) is reaffirmed as handwashing is one of the ways to prevent Coronavirus infection and other diseases. The campaign will continue to raise awareness on the same along with focussing on the importance of nutrition and healthcare for women and children, fight malnutrition, mental wellbeing, self care, science and health, adolescent health & gender awareness. Along with the health of people, the campaign has realised the need to also take care of the health of the eco-system. Our environment is fragile due to human activity, which is not only over-exploiting available resources, but also generating immense pollution as a result of using and extracting those resources. The imbalance has also led to immense biodiversity loss that has caused one of the biggest threats to human survival – climate change. It has now been described as a “code red for humanity.” The campaign will continue to cover issues like air pollution, waste management, plastic ban, manual scavenging and sanitation workers and menstrual hygiene. Banega Swasth India will also be taking forward the dream of Swasth Bharat, the campaign feels that only a Swachh or clean India where toilets are used and open defecation free (ODF) status achieved as part of the Swachh Bharat Abhiyan launched by Prime Minister Narendra Modi in 2014, can eradicate diseases like diahorrea and the country can become a Swasth or healthy India.
