Molecular Characterization of Dengue Viruses Causing Hemorrhagic Fever from the Atypical Dengue Cases in Chennai, India

Objectives:The classic presentation of dengue fever has expanded its horizon by involving severe forms as atypical manifestations and hemorrhagic fever with reason unknown.This study aimed to characterize dengue viruses (DENV) causing hemorrhagic fever. Methods:Clinically suspected cases of dengue fever were confirmed by NS1 antigen, IgM and IgG antibody.Following clinical confirmation dengue virus isolates were subjected to reverse transcriptase polymerase chain reaction (RT-PCR), sequenced, aligned using Clustal W and serotype based phylogenetic analysis was performed.Results: A total of 308 cases were screened, during 2015-18 of which 106 (34%) samples were positive for dengue infection.42 (40%) cases showed atypical dengue manifestations, 14 (13%) presented with hemorrhagic fever.Among the atypical manifestations, hepatomegaly and splenomegaly were the most common, followed by ascites 12 (11%), pleural effusion 9 (8%), bradycardia 6 (6%), meningitis 6 (6%), acalculous cholecystitis 04 (4%), haemoptysis 3 (3%) and acute pancreatitis 2 (2%).Dengue hemorrhagic fever (n = 14) was caused by, DENV-1 (n = 7), DENV-2 (n = 5) and DENV-4 (n = 2).Serotype DENV-3 was not isolated in any of the samples.A new clade of genotype I (GI) was predominant in DENV-1; Genotype IVC (GIVC)was predominant in DENV-2 showing mixed clustering suggesting lineage C; clade B of lineage C, genotype I (GI)was seen in DENV-4.The amino acid changes were observed in M51I, L72F, S93N in DENV-1 and M104V, V112A in DENV-2 of C-prM regions of hemorrhagic isolates when compared to standard strains.