Dengue virus underwent dramatic evolution in India, says new study
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Bengaluru: The dengue virus has evolved dramatically in India over the last five decades. Researchers of the study said that the new strains of the virus demand the development of new vaccines.
According to the scientists at the Indian Institute of Science (IISc), South-East Asian countries have seen a steady rise in dengue cases in the last 50 years. But, there are no approved vaccines against the disease in India.
Rahul Roy, Associate Professor at the Department of Chemical Engineering at IISc Bengaluru, told PTI that the team is trying to understand how different the Indian variants are. "We found that they are very different from the original strains used to develop the vaccines."
The team examined 408 available genetic sequences of Indian dengue strains collected from patients between 1956 and 2018. A computational analysis was used to examine how much of these serotypes deviated from their ancestral sequence, from each other, and from other global sequences. They found that the sequences are changing in a "very complex fashion".
Findings also suggest that until 2013, the dominant strains in the country were Dengue 1 and 3. But, in recent years, Dengue 2 has become dominant. Dengue 4 which was once considered the least infectious is becoming more prominent in South India. "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," added the experts.
The team also tried to find out what factors decide which strain is dominant. According to the first author Suraj Jagtap, one possible factor is Antibody-Dependent Enhancement (ADE). It happens when antibodies are generated during an immune response to recognise and bind to the pathogen. But these are unable to prevent infection and end up acting like a Trojan horse that allows pathogens to get into cells.
"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. 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," said Roy.
The team is trying to find out if ADE can also change the evolution of the virus.
They also found that such interdependence between the dengue virus and the immunity of the human population has not been found 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."
