A single amino acid in nonstructural protein NS4B confers virulence to dengue virus in AG129 mice through enhancement of viral RNA synthesis.

Dengue (DEN) is a mosquito-borne viral disease that has become an increasing economic and health burden for the tropical and subtropical world. The lack of an appropriate animal model of DEN has greatly impeded the study of its pathogenesis and the development of vaccines/antivirals. We recently reported a DEN virus 2 (DENV-2) strain (D2Y98P) that lethally infects immunocompromised AG129 mice, resulting in organ damage or dysfunction and increased vascular permeability, hallmarks of severe DEN in patients (G. K. Tan et al., PLoS Negl. Trop. Dis. 4:e672, 2010). Here we report the identification of one critical virulence determinant of strain D2Y98P. By mutagenesis, we showed that a Phe-to-Leu alteration at amino acid position 52 in nonstructural protein NS4B completely abolished the pathogenicity of the D2Y98P virus, as evidenced by a lack of lethality and the absence of histological signs of disease, which correlated with reduced viral titers and intact vascular permeability. Conversely, a Leu-to-Phe alteration at position 52 of NS4B in nonvirulent DENV-2 strain TSV01 led to 80% lethality and increased viremia. The NS4B(Phe52) viruses displayed enhanced RNA synthesis in mammalian cells but not in mosquito cells. The increased viral RNA synthesis was independent of the ability of NS4B to interfere with the host type I interferon response. Overall, our results demonstrate that Phe at position 52 in NS4B confers virulence in mice on two independent DENV-2 strains through enhancement of viral RNA synthesis. In addition to providing further insights into the functional role of NS4B protein, our findings further support a direct relationship between viral loads and DEN pathogenesis in vivo, consistent with observations in DEN patients.

Interferon alfacon 1 inhibits SARS-CoV infection in human bronchial epithelial Calu-3 cells.

The primary targets for SARS-CoV infection are the epithelial cells in the respiratory and intestinal tract. The angiotensin-converting enzyme 2 (ACE-2) has been identified as a functional receptor for SARS-CoV. ACE-2 has been shown to be expressed at the apical domain of polarized Calu-3 cells. In this report, interferon alfacon 1 was examined for inhibitory activities against SARS-CoV on human lung carcinoma epithelial Calu-3 cell line and the other three African green monkey kidney epithelial cell lines. Interferon alfacon 1 demonstrated significant antiviral activity in neutral red uptake assay and virus yield reduction assay. The data might provide an important insight into the mechanism of pathogenesis of SARS-CoV allowing further development of antiviral therapies for treating SARS infections.

An Outbreak of Community Associated Methicillin Resistant Staphylococcus aureus Subtype USA300 at an International School in Singapore.

Community associated methicillin-resistant Staphylococcus aureus (CA-MRSA) subtype USA300 remains relatively well confined within North American shores. Between August and November 2010, a large international school in Singapore recorded 27 skin and soft tissue infections, 8 of which were confirmed USA 300. This study reports the outbreak investigation and the interventions instituted.