Genetic characterization of dengue virus serotypes causing concurrent infection in an outbreak in Ernakulam, Kerala, South India.

Dengue fever, a mosquito-borne viral infection, causes significant morbidity and has become endemic in the Indian subcontinent. Virus strains currently circulating in many parts of the country are not well studied at the molecular level. In the present study, genetic characterization of virus strains from a dengue outbreak that occurred in and around a tertiary care hospital in Ernakulam, Kerala in the year 2008 has been reported. By reverse transcription polymerase chain reaction (RT-PCR), 37 out of 75 (49.3%) clinically suspected cases were positive for dengue viral RNA. Among these, 21 (56.8%) samples showed concurrent infection with multiple serotypes of the virus. Majority of the combined infections were caused by dengue serotype 2 and 3. Co-infections with type 1 and 2 in two patients, and type 1, 2 and 3 in one patient were also observed. The core-pre-Membrane (CprM) junction nucleotide sequencing and phylogenetic analysis revealed that the type 1 strains were related to the viral strains reported from Delhi-2001 and Gwalior-2002 dengue outbreaks, while the type 2 strains were related to the strains from Gwalior-2001 epidemic. Sequences of type 3 strains did not show clear relation to any of the previous Indian isolates, and in the phylogenetic analysis, they formed a distinct lineage within the Indian type 3 strains. This study indicates hyperendemicity of dengue in the region with the presence of multiple serotypes and high rates of co-infection, and local genomic evolution of the viral strains involved in this outbreak.