According to a study published in the journal PLoS Pathogens, researchers from the Indian Institute of Science (IISc) revealed that the dengue virus has evolved to be more severe in India. In the multi-institutional study, the researchers showed how the virus causing the disease has evolved dramatically over the last few decades in the Indian subcontinent.

Dengue fever, a mosquito-borne viral illness, has progressively grown in the last 50 years, mostly in Southeast Asian nations. In the study, the researchers investigated all 408 known genetic sequences of Indian dengue strains collected from patients by other researchers as well as the team between 1956 and 2018.

Dengue virus is classified into four serotypes, namely dengue 1, 2, 3, and 4. The researchers used computational analysis to determine how much each of these serotypes differed from their original sequence, from each other, and from other worldwide sequences. According to the findings of the study, dengue 2 has become increasingly prevalent across the country in recent years, whereas dengue 4, formerly thought to be the least contagious, has found a niche in South India.

The researchers also noted that if the second serotype is similar to the first, then the antibodies in the blood of the host produced after the first infection bind to the new serotype. They also found that, at any given time, several strains of each serotype existed in the viral population. This proximity allows the newcomer to infect macrophages, making the infection more severe.

Based on the studys findings, the researchers argued that if the body gets infected by a similar but not identical viral strain, antibody-dependent enhancement (ADE) kicks in, providing the new strain with a large advantage. This allows the new strain to become the dominant strain in the population. The researchers explained that this was the cycle through which the current Dengue 4 strains replaced the Dengue 1 and 3 strains. 

(Source: https://www.ndtv.com/india-news/dengue-virus-evolved-dramatically-in-india-in-last-few-decades-says-study-3998289)