Investigation of a Chikungunya-like illness in Tirunelveli district, Tamil Nadu, India 2009-2010

Abstract

Objective: To identify the aetiological agent/s of an outbreak of chikungunya-like illness with high morbidity and several fatalities in Tamil Nadu, India, 2009-2010. Methods: Two hundred and seventeen serum samples were collected from the affected areas and screened for chikungunya virus (CHIKV), dengue virus (DENV) and Japanese encephalitis virus (JEV) IgM antibodies using MAC-ELISA kits. A few selected samples were also tested for Ross River, Sindbis, and Murrey Valley viruses by RT-PCR and Hantan virus by serology. Twelve acute serum and mosquito samples were processed for virus isolation in C6/36 cells. CHIKV isolate was characterised by RT-PCR and sequencing. Results: Diagnostic levels of IgM antibodies were detected in 107 (49.3%) CHIKV samples and 22 (10.1%) DENV samples. IgM antibodies against JEV were not detected (n=46). Characterisation of the CHIKV isolate at genetic level demonstrated it as ECSA (E1: 226A). Thirty-six selected samples were also negative for Ross River, Sindbis, Murrey Valley and Hantan viruses. Conclusion: High prevalence of CHIKV IgM antibody positivity, clinical symptoms, virus isolation and the presence of vector mosquitoes clearly suggest CHIKV as the aetiological agent responsible for the outbreak.