Prevalence of West Nile virus infection in India.

During the course of the virological investigation of cases of suspected viral fevers carried out at the National Institute of Virology (NIV), Pune, India, evidence of recent infection with West Nile (WN) virus was detected in 88 cases. Fever, general aches, headache, nausea and vomiting were the principal clinical features in 92% (81/88) of the cases; there were seven cases of encephalitis, in which WN virus-specific IgM class antibodies were detected in CSF samples. These cases of encephalitis were from Japanese encephalitis (JE) nonendemic areas, like Maharashtra and Rajasthan, as well as from JE endemic areas, like Goa and Orissa. Interestingly, neutralizing antibodies predominantly to WN virus were detected in CSF samples by the 50% cytopathic effect inhibition method; the titers ranged from 5 to 375. Cases of WN virus infection associated with both encephalitis and classic features have been reported for the first time in recent years in India. Reports of unique urban West Nile virus encephalitis epidemics in New York, Romania, and Algeria in recent years have signaled the emergence of neurological infection due to West Nile virus as a novel public health threat. This study is important because it records evidence of WN virus infection in India.