Sequence analysis of E/NS1 gene junction of Dengue Type-1 viruses isolated in Klang Valley 2010 to 2012

Dengue is a mosquito-borne viral disease caused by four serotypes of dengue virus, affecting the human population for decades in many tropical and subtropical regions of the world. In Malaysia, all four dengue serotypes co-circulates in a dengue season even though any one of the serotypes can predominate. In this study, serum samples were collected from dengue fever and severe dengue fever patients within Klang Valley from 2010-2012 to determine the prevailing dengue serotypes. In addition, sequencing of the envelope/nonstructural 1 (E/NS1) gene junction of the virus isolated was performed to identify the presence of any mutations that are suggestive of increased virulence in the virus. The results showed that Dengue-1 (DEN-1) was the predominant circulating serotype. The E/NS1 gene sequences of the isolates were analysed to trace the evolutionary knowledge of the strains. All sequences of the isolates were compared with DEN-1 prototype Hawaii strain as the reference sequence. The E/NS1 sequences of other dengue strains from neighbouring regions as well as other parts of the world obtained from the GenBank database were also included in the phylogenetic tree analysis. Analyses showed that there was 97% to 100% similarity among the ten isolates at the nucleotide level. Similarly, the amino acid analogue also showed 98% to 100% homology. However, all five non-severe dengue isolates showed variation at position 780, resulting in an amino acid change from valine to alanine as compared to severe dengue isolates. A rooted phylogenetic tree was performed using neighbour-joining method with DEN-2 and DEN-3 as the outgroups. Results showed that all ten isolates were classified as genotype I. In addition, the five isolates from severe dengue patients were found to be clustered together with JN697057 and JN697058, Malaysian DEN-1 strains from the 2005 outbreak.