 DENV-1 serotype was detected in 63% samples28. Our results show a change in serotype dominance from Dengue virus type 1 in 2010 to dengue virus type 2 in 2013 in Delhi.
Co-infection with more than one dengue virus serotypes was also detected (14%) in the present investigation. Bharaj et al had reported concurrent infection in 19% of the positive samples in 2006 in Delhi27. A very high percentage of co-infection by different serotypes (56.8%) was reported from Kerala, Southern state of India in 200829 . DENV-1 strains of American African genotype, DENV-2 strains of the Cosmopolitan genotype and DENV-3 strains of Genotype III were detected in the 2013 outbreak.. The genotypes reported in the present study are known to be circulating in India in recent years (Afreen, unpublished data,23,30,31). Alteration in circulating DENV-1, 2 and 3 genotypes was not observed in the year 2013. This may be due to complete dominance of these genotypes over any other genotype which may have been imported but failed to establish. Another factor could be a selective advantage of these genotypes in Indian hosts (both human and mosquito) or in Indian climate.
Molecular detection and serotyping of dengue viruses were carried out on acute phase blood samples that were collected during 2013 dengue fever outbreak from Delhi. Dengue viruses were detected in more than two third of the samples. Dengue virus serotype 2 was detected as the dominant serotype in the outbreak. Co-infection by different serotypes was also detected in the outbreak. Twenty nine outbreak strains (10 DENV-1, 12 DENV-2 and 7 DENV-3) were sequenced for partial envelope gene. Phylogenetic analysis grouped DENV-1 strains in the American African genotype, DENV-2 strains in the Cosmopolitan genotype and DENV-3 in Genotype III. The study will be helpful in the study of the epidemiology of dengue fever.
The authors have declared that no competing interests exist.
AcknowledgementsNazia Afreen is supported by Senior Research Fellowship of the University Grants Commission, Government of India.
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