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Introduction: Dengue virus (DENV), the causative agent of dengue disease exists in sylvatic and endemic ecotypes. The cell morphological changes and viral morphogenesis of two dengue ecotypes were examined at the ultrastructural level to identify potential similarities and differences in the surrogate model of enzootic host., Materials and Methods: Vero cells were inoculated with virus at a multiplicity of infection (MOI) of 0.1. Cell cultures were harvested over a time course and processed for transmission electron microscopic imaging., Results: The filopodia protrusions on cell periphery preceded virus entry. Additionally, sylvatic DENV infection was found spreading slower than the endemic DENV. Morphogenesis of both dengue ecotypes was alike but at different level of efficiency in the permissive cells., Conclusions: This is the first ultrastructural study on sylvatic DENV and this comparative study revealed the similarities and differences of cellular responses and morphogenesis of two dengue ecotypes in vitro. The study revealed the weaker infectivity of sylvatic DENV in the surrogate model of enzootic host, which supposed to support better replication of enzootic DENV than endemic DENV.

Identification of the aetiologic agent(s) associated with an outbreak of fatal childhood viral infection in Sarawak, Malaysia, in mid 1997 remains elusive. It is reported here that African green monkey kidney (Vero) and human monocytic (U937) cells treated with inocula derived from clinical specimens of some of these fatal cases showed the presence of cellular genomic DNA degradation when the extracted DNA was separated by pulsed field gel electrophoresis (PFGE), oligonucleosomal DNA ladders characteristic of apoptotic cells when the infected cells' DNA was separated by agarose gel electrophoresis, and apoptotic cellular DNA fragmentation when cells were stained using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL). These results suggest that inocula derived from the patients' clinical specimens contain factors which stimulate apoptotic cellular responses in vitro.

The present study was undertaken to investigate the antibody responses of dengue fever (DF) patients to specific dengue virus proteins. Partially purified dengue 2 New Guinea C (NGC) strain virus was used as antigen. Under the present experimental protocols, it was observed that almost all DF patients' sera had detectable presence of antibodies which recognize the dengue 2 envelope (E) protein. The convalescent-phase sera especially had significant detectable IgG, IgM and IgE against the protein. In addition, IgGs specific against the NS1 dimer and PrM were also detected. Antibody against the core (C) protein, however, was not detectable in any of the DF patients' sera. The substantial presence of IgG against the PrM in the convalescent-phase sera, and the presence of IgE specific for the E, reflect the potential importance of these antibody responses in the pathogenesis of dengue.