A Comprehensive Study on the 2012 Dengue Fever Outbreak in Kolkata, India

Background. Dengue viruses (DV) belong to the family Flaviviridae, with four serotypes referred to as DV-1, DV-2, DV-3, and DV-4. A large-scale outbreak of dengue fever occurred in 2012 involving several districts of West Bengal. Objective. To present a comprehensive picture of the dengue fever outbreak in 2012 and to identify the prevailing serotypes. Materials and Methods. Serum samples were collected from suspected dengue fever cases. Samples from fever cases <5 days duration were tested for dengue NS1 antigen employing Pan Bio (Australia) NS1 ELISA kit. Serum samples of ≥5 days fever were tested for dengue-specific IgM by MAC ELISA test kit prepared by the National Institute of Virology Pune, India. Serotyping of dengue samples was done by dengue-specific reverse transcriptase polymerase chain reaction (RT-PCR). Results. The number of dengue cases in 2012 clearly outnumbered the dengue cases in 2010 and 2011. The majority of the cases were in the age group 11–30 years with a male preponderance. Outbreak occurred during the months of Aug.–Nov. indicating increased vector transmission in the monsoon and postmonsoon periods. The prevailing serotypes in this outbreak were Den1, Den3, and Den4. 1. Introduction Dengue viruses (DV) belong to the family Flaviviridae, and there are four serotypes of the virus referred to as DV-1, DV-2, DV-3, and DV-4 [1]. DV is a positive-stranded encapsulated RNA virus and is composed of three structural protein genes, which encode the nucleocapsid or core (C) protein, a membrane-associated (M) protein, an enveloped (E) glycoprotein, and seven nonstructural (NS) proteins. It is transmitted mainly by Aedes aegypti mosquito and also by Ae. albopictus. All four serotypes can cause the full spectrum of disease from a subclinical infection to a mild self-limiting disease, the dengue fever (DF), a severe disease that may be fatal, and the dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS). Dengue is the most common and widespread arboviral infection in the world today. It is an increasingly prevalent tropical arbovirus infection with significant morbidity and mortality [1]. dengue infection has been known to be endemic in India for over two centuries as a benign and self-limited disease. In recent years, the disease has changed its course manifesting in the severe form as DHF and with increasing frequency of outbreaks [2]. dengue infection in a previously nonimmune host produces a primary response of antibodies characterized by a slow and low-titer antibody response. IgM antibody is the first immunoglobulin isotype to