Co-circulations of two genotypes of dengue virus in 2006 out-break of dengue hemorrhagic fever in Karachi, Pakistan

Background: The status of dengue genotypes involved in the recent epidemic out-breaks in Pakistan is not well defined. Objectives: We sought to analyze the predominant genotype responsible for the most severe and largest out-break of dengue hemorrhagic fever (DHF) that hit Karachi in 2006. Study design: Retrospective analysis of stored serum samples for dengue virus genotype by multiplex RT-PCR, anti-dengue IgM, IgG and review of clinical charts of patients admitted to Aga Khan University Hospital. Results: Viral RNA detection of 250 patients revealed positive results in 185 (74.0%) samples. DEN-2 was predominant genotype (n = 104, 56.2%) Dengue specific antibodies were detected in 139 samples of which 81 were classified as primary cases. DEN-2 accounted for these. Within secondary cases, 63.2% were due to DEN-2 (total 57), the rest were positive for DEN-3. DHF (p = 0.064) and abdominal pain (p = 0.059) were more frequently associated with DEN-2 as compared to DEN-3. None of the samples were positive for DEN-1 or DEN-4. Conclusion: Co-circulation of DEN-2 and DEN-3 was responsible for the 2006 out-break in Karachi. Primary and secondary cases were seen in both groups. Cases with DHF showed marginal association with DEN-2. Introduction of a new serotype (DEN-3) and or a genotypic shift of endemic serotype (DEN-2) are the probable factors for the recent out-break of DHF in this region.