Dengue and Dengue Haemorrhagic Fever Outbreak in Pondicherry, South India, during 2003-2004: Emergence of DENV-3

During October 2003 - February 2004, a suspected outbreak of dengue fever and dengue haemorrhagic fever occurred in Pondicherry and the present investigation was carried out to confirm the dengue epidemic through clinical, serological and molecular studies. Analysis of clinical symptoms showed that the younger age group of 1-15 years was the most affected (65%, n=28). Of the 79 serologically- confirmed dengue cases at hospitals and clinics, 64 were positive for IgM antibodies reflecting current (primary) infections. Viral infection was also confirmed by testing IgM-positive samples by intracerebral inoculation of Toxorhynchitis splendens and indirect immunofluorescence using anti-dengue virus antibodies. Nested reverse transcriptase (RT) PCR assay (capsid region) yielded amplicon of the size 290 bp, diagnostic for DENV-3 for 32 samples. Sequence analysis of the amplicon confirmed the serotype and phylogenetic analysis of sequence showed closeness of the Pondicherry isolate to the Peru/Taiwan strains. Three health blocks were found to be the risk areas for the transmission of dengue infection, which also recorded moderate-to-high breeding of Aedes aegypti, and to a lesser extent of Ae. albopictus. High breeding of Ae. aegypti and detection of clustering of cases indicated this vector species playing a major role in the outbreak of dengue in Pondicherry.