Epidemiology of Dengue Fever in India

Introduction
Dengue fever or dengue hemorrhagic fever is an acute mosquito-borne viral disease transmitted by female Aedes aegypti and Aedes albopictus mosquito. The dengue virus has four serotypes, namely DENV-1, DENV-2, DENV-3, and DENV-4. Every year nearly 100 million people get infected with dengue fever, and almost 40000 deaths are recorded. According to WHO, the number of positive cases of dengue fever globally has increased eight times over the last two decades. The mortality report of dengue reported to WHO between 2000 and 2015 has increased from 960 to 4032.

The risk of dengue exists in tropical and subtropical climates of Central America, South America, Africa, Asia, and Oceania. Long-term travelers and humanitarian workers who travel to locations where Dengue fever is prevalent are particularly vulnerable. Dengue fever can be found in urban and suburban areas, with transmission rates peaking during the rainy season. India has confirmed Dengue cases with cases reported from across the country. Dengue is endemic in India. Transmission occurs year-round in southern areas and from April through November in northern states.

This article provides an overview of dengue fever epidemiology in India. It begins with an overview of the early cases of dengue fever in India, followed by a population-based case study of the current dengue situation in India. Finally, the article presents the positive cases and mortality rates associated with dengue fever reported from 2015 to 2021.

Epidemiology of Dengue Fever in India
Dengue fever has been a problem in India since 1956 when the etiology was discovered by isolating DEN 2 from a six-year-old child’s serum in Vellore. In subsequent years the remaining three serotypes were isolated in India. The incidence of dengue from 1956-2010 with the responsible serotype presented by researcher G. Pandya in his article “ Prevalence of Dengue Infection in India” and Sakshi Srivastava et al. in their scientific article “ Dengue in India” is mentioned below in Table 1.

Table 1: Incidence of dengue Infection in India from 1956-2010

In a cross-sectional population-based or community-based serosurvey, an Indian team of researchers aimed to assess the age-specific seroprevalence, type of infection, and the number of dengue infections in India. The survey results were later published in the Lancet Journal in 2019. The study involved individuals of three age groups (5–8 years, 9–17 years, and 18–45 years) from each of the five geographical regions of India, namely north, east, west, south, and northeast. The researchers randomly selected three states from each geographical area. From each of these three states, four districts were established. Each of these districts was divided into four clusters. Two clusters represented the study population from rural wards and the other two from urban communities. Thus, the entire study involved 15 states, 60 districts, and 240 clusters. At the end of the screening, there were 4059 volunteers between 5-8 years, 4265 volunteers between 9-17 years, and 3976 volunteers between 18-45 years as participants, making the study’s total sample size 12300 volunteers. After getting approval from the ICMR’s Institutional Ethics Committee and all other participating institutes, the survey was carried out.

The study procedure was simple. First, the researchers collected 3 ml of venous blood from the volunteers and separated the serum. Then, the serums or sera were tested for IgG antibodies using the Indirect ELISA method. Graphs 1 and 2 illustrate the seroprevalence of IgG antibodies observed in the survey according to age group and sex. Again, 100 samples were chosen randomly from each region and analyzed using the plaque reduction neutralization test (PRNT90) against the four dengue virus serotypes.

The survey results showed that the seroprevalence of dengue increased with age. However, younger children showed a higher force of infection. Seroprevalence of dengue was highest in the southern region (76.9%), followed by the western part (62.3%), northern region (60.3%), and lowest in the northeast region (5.0%). The study also showed that the seroprevalence was higher in urban clusters (70.9%) than the rural clusters (42.3%). The researchers also found the distribution of serotype-specific antibodies of dengue fever among the study population. The DENV-1 and DENV-2 serotype-specific antibodies were predominant in the northern and eastern regions. The western and southern regions had the DENV-1, DENV-2, and DENV-3 serotype-specific antibodies. The north-eastern area was found to have the DENV-3 serotype-specific antibody. Thus the study concluded that dengue fever has a heterogeneous seroprevalence in the different regions in India.