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

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.