Serological & virological investigation of an outbreak of dengue fever in Gwalior, India

Abstract

Background & objectives: An outbreak of febrile illness occurred between September to November 2001 in Gwalior, Madhya Pradesh affecting individuals mostly in the age group < 30 yr. A total of 312 febrile indoor patients suspected to have dengue infection were investigated.

Methods: The investigation included examination of blood samples from patients for dengue specific IgM and IgG antibodies, isolation of virus in suckling mouse pups and in C(6/36) cell line followed by confirmation and typing through reverse transcriptase-PCR and nested PCR.

Results: The serological analysis of the 312 samples indicated 65 per cent positivity of which 21 per cent are of recent infection as indicated by the presence of IgM antibody and 78 per cent are found to be secondary in nature by showing the presence of IgG and/or IgM antibodies. The RT-PCR analysis of patients' sera employing dengue virus group specific conserved amplimer confirmed the etiological agent as dengue complex by showing the characteristic 511 bp amplicons. None of the antibody positive samples were found to be positive by RT-PCR. A total of 13 (6%) samples positive by RT-PCR, were processed for virus isolation in mouse pups and in C(6/36) cells. Of these 9 samples (80%) were confirmed positive for virus isolation as identified by RT-PCR.

Interpretation & conclusion: The typing of isolates by nested PCR employing serotype specific amplimer revealed 119 bp amplicon characteristic of dengue virus type-2 and thus confirming the outbreak attributed to dengue virus type-2.