An outbreak of chikungunya in southern Thailand from 2008 to 2009 caused by African strains with A226V mutation

Objectives: To elucidate clinical and molecular characteristics of chikungunya fever (CHIK fever) from the 2008-2009 outbreak caused by chikungunya virus (CHIKV) in southern Thailand. Methods: Three hundred and eighty-one sera from 332 patients with acute febrile illness were tested for anti-CHIKV IgM antibody by ELISA. A molecular analysis of these sera was performed using a semi-nested reverse transcriptase polymerase chain reaction (RT-PCR), followed by direct sequencing and phylogenetic analysis. Results: One hundred and seventy-nine patients were diagnosed with CHIK fever by molecular analysis and/or anti-CHIKV IgM antibody detection. Patients diagnosed with CHIK fever were significantly older than controls (mean age 38.8 +/- 19 vs. 28.7 +/- 18 years, p < 0.0001) and presented with arthralgia more often than controls. One hundred percent of the sera were positive by RT-PCR, whereas only 10% were positive in serological tests for anti-CHIKV IgM antibody by ELISA if the serum was obtained during the first 4 days of fever. In contrast, CHIKV-specific IgM antibody by ELISA was found in 100% of patients, whereas 15% of patients were positive by RT-PCR if the serum was obtained more than 9 days after the onset of fever. RT-PCR for CHIKV should be performed if the patients present within the first 4 days of fever. Patients presenting after at least 9 days of fever should be tested for IgM antibody. Based on phylogenetic analysis, the CHIKV strains isolated belong to African genotypes harboring the E1 A226V mutation, indicating a single origin of the 2004-2009 CHIKV outbreaks. Conclusions: The novel CHIKV mutation could potentially modify the epidemiological presentation of CHIK fever. Early diagnosis of CHIK fever is essential for preventing further massive outbreaks. (C) 2010 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.