S.12. Serological and molecular investigation of a dengue outbreak in Mumbai, India

The recent emergence of dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS) in India has been a source of major public health concern. There are four serotypes of dengue viruses and all the four serotypes were isolated from different outbreaks in India. In this study, we investigated sudden outbreak of a dengue epidemic in Mumbai during August-September, 2005 following heavy flood. A total of 111 serum samples from dengue suspected patients were collected from various hospitals in Mumbai. The serosurveillance was carried out using an in-house nitrocellulose membrane based indirect Dipstick ELISA and the results were compared with commercially available PanBio ICT kit. The Dipstick ELISA result revealed 14 samples positive for IgM antibodies, suggestive of recent or primary infection, 20 samples positive for IgG antibodies and 8 samples positive for both IgM and IgG antibodies suggestive of secondary infection. The comparison of Dipstick ELISA with PanBio ICT showed 84% and 86% concordance for detection of IgM and IgG antibodies respectively in patient sera. The RT-PCR analysis employing dengue complex specific consensus primers revealed a total of 7 serum samples to be positive for the presence of dengue specific amplicon (511bp). Further serotyping by Multiplex PCR with serotype specific primers revealed 230 bp amplicons characteristic of Dengue virus type-2, which was later confirmed by nucleotide sequencing. Attempts to isolate virus from RT-PCR positive samples in C_6/36 cell line resulted in isolation of one dengue virus type-2 as confirmed through dengue virus serotype specific multiplex PCR and nucleotide sequencing. Thus present study confirmed the outbreak in Mumbai and adjoining area following the unprecedented flood was due to dengue virus implicating serotype–2 as the etiological agent.