Dengue fever, a mosquito-borne viral disease, has become a major public health concern in India. Scientists from the Indian Institute of Science (IISc) have conducted a computational analysis of the dengue virus over six decades and found that it has evolved dramatically. The research, which examined 408 genetic sequences of Indian dengue strains from infected patients collected between the years 1956 and 2018, revealed that the cases of mosquito-borne viral disease have steadily increased in the last 50 years, predominantly in South-East Asian countries.

The dengue virus belongs to the Flaviviridae family and has four serotypes. The virus is transmitted to humans by the Aedes mosquito, which becomes infected by biting an infected person. Once the virus enters the human body, it replicates in white blood cells called monocytes and macrophages, which are a part of the body’s immune system. The virus then spreads to other organs, including the liver, spleen, and lymph nodes, causing a range of symptoms.

The study found that the sequences of the dengue virus are changing in a very complex fashion. Until 2012, the dominant strains in India were Dengue 1 and 3. However, Dengue 2 has become more dominant across the country in recent years, while Dengue 4, once considered the least infectious, is now making a niche for itself in South India.

Suraj Jagtap, first author of the study, 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 bind to immune cells called macrophages.

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. The new findings further show how important it is to develop a vaccine for the disease.