Dengue virus (DENV) is a leading cause of morbidity and mortality in most tropical and subtropical areas of the world. Dengue virus infection induces specific CD4+CD8– and CD8+CD4– T cells in humans. In primary infection, T-cell responses to DENV are serotype cross-reactive, but the highest response is to the serotype that caused the infection. The epitopes recognized by DENV-specific T cells are located in most of the structural and non-structural proteins, but NS3 is the protein that is most dominantly recognized. In patients with dengue hemorrhagic fever (DHF) caused by secondary DENV infection, T cells are highly activated in vivo. These highly activated T cells are DENV-specific and oligoclonal. Multiple kinds of lymphokines are produced by the activated T cells, and it has been hypothesized that these lymphokines are responsible for induction of plasma leakage, one of the most characteristic features of DHF. Thus, T-cells play important roles in the pathogenesis of DHF and in the recovery from DENV infection.

BACKGROUNDTo study the molecular biology of Xinjiang hemorrhagic fever (XHF) viruses, to explore its relationship with other Crimean-Congo hemorrhagic fever viruses, analyzing the epidemic origin and the tendency of geographic distribution of XHF.

METHODSThe S partial segment from the patient and tick samples collected in 2001 and 2002 was tested by RT-PCR, the positive samples were sequenced directly. The nucleotide homology of S partial segment as well as the whole segments were analyzed and the phylogenetic tree of S and M gene segments was drawn by computer.

RESULTSAll compared sequences of S partial segments from the patient and tick samples showed a high homology of nucleotide sequences. Phylogenetic tree divided all the analyzed viruses into three groups; Europe, African and Asian group. The Asian group can be divided further into another two branches: the middle Asian branch and the Chinese branch. All the Chinese isolates were clustered into one single group and was easy to be discriminated from the other isolates. The dividing of M segments seemed not completely related to the geographic origin of the viruses.

CONCLUSIONM segment classification was not consistent to the geographic distribution of the viruses. S segments analysis showed the close relationship of genetic background between the patient isolates and the tick isolates. Besides, all the Chinese isolates have the common evolution route and the gene structure characteristics displayed the regional distribution pattern.

Animals ; China ; epidemiology ; Genetic Variation ; Hemorrhagic Fever Virus, Crimean-Congo ; classification ; genetics ; isolation & purification ; Hemorrhagic Fever, Crimean ; epidemiology ; virology ; Humans ; Molecular Epidemiology ; Phylogeny ; RNA, Viral ; genetics ; Reverse Transcriptase Polymerase Chain Reaction ; Sequence Analysis, DNA ; Ticks ; virology ; Viral Proteins ; genetics

Dengue is an emerging disease in Nepal and was first observed as an outbreak in nine lowland districts in 2006. In 2010, however, a large epidemic of dengue occurred with 4,529 suspected and 917 serologically-confirmed cases and five deaths reported in government hospitals in Nepal. The collection of demographic information was performed along with an entomological survey and clinical evaluation of the patients. A total of 280 serum samples were collected from suspected dengue patients. These samples were subjected to routine laboratory investigations and IgM-capture ELISA for dengue serological identification, and 160 acute serum samples were used for virus isolation, RT-PCR, sequencing and phylogenetic analysis. The results showed that affected patients were predominately adults, and that 10% of the cases were classified as dengue haemorrhagic fever/ dengue shock syndrome. The genetic characterization of dengue viruses isolated from patients in four major outbreak areas of Nepal suggests that the DENV-1 strain was responsible for the 2010 epidemic. Entomological studies identified Aedes aegypti in all epidemic areas. All viruses belonged to a monophyletic single clade which is phylogenetically close to Indian viruses. The dengue epidemic started in the lowlands and expanded to the highland areas. To our knowledge, this is the first dengue isolation and genetic characterization reported from Nepal.