Clinical and virological characterization of imported cases of Chikungunya fever.

A Chikungunya virus (CHIKV) epidemic emerged in the Indian Ocean islands of the Comores, Reunion, Mayotte, Mauritius, the Seychelles and Madagascar in 2005 resulting in the infection of about 250.000 inhabitants and travellers in only one year. Beginning in March 2006 increasing numbers of CHIKV-like febrile illnesses were reported from various parts of India. We investigated 70 consecutive German travellers returning from the affected areas and presenting with arthralgia and/or fever suggestive of CHIKV infection. Eleven patients had serological evidence of CHIKV infection. Real-time RT-PCR for CHIKV was positive in two cases, one who returned from Mauritius and the other who came back from Rajasthan, Northern India. In both cases CHIKV was isolated and sequencing of the entire viral genome was performed. The nucleotide sequence data obtained for both CHIKV strains revealed a high level of identity to CHIKV isolates from the ongoing epidemic. In detail, we found only 18 nucleotide exchanges between the isolates from Mauritius and Rajasthan, resulting in only six amino acid changes (nsP1 T128K, T376M, nsP3 S472N, capsid P23S, V27I and E1-protein A226V). Although the excessive dimension of the 2005/2006 outbreak in the Indian Ocean islands was at least in part accounted to the naïve population affected, our results of the Rajasthan isolate support that the emergence of this CHIKV subtype may rather be a result of a better viral fitness. This has been previously accounted to a A226V change in the E1 protein of the new CHIKV variant when compared to other CHIKV data available. This mutation, supposedly resulting in high-titred viremia in humans and/or an enhanced adaptation to the vector population resulting in increased transmission rates, was also found in our CHIKV isolate from Mauritius. The spread of an African CHIKV to Asia further demonstrates how fast viruses can emerge and establish in places where competent vectors are prevalent.