Characterisation of Nelson Bay virus infection

Since 1999, six novel viruses belonging to the Nelson Bay orthoreovirus species group have been described throughout Malaysia and Asia. Four of these viruses were isolated from human patients suffering from acute respiratory disease, the first time that orthoreoviruses have been reported to cause significant disease symptoms in humans. The remaining viruses from this group were isolated from Pteropid bats, and sequence similarity as well as epidemiological evidence suggests that all members Nelson Bay orthoreoviruses originated in Pteropid bats. Nelson Bay virus (NBV) was isolated in Australia in 1968 from the blood of a grey-headed flying fox during routine sampling in New South Wales, Australia. Apart from limited early characterization studies, little is known regarding the host range or pathogenicity of NBV. Due to the unknown nature of this virus and its close genetic relatedness to orthoreoviruses capable of causing disease in humans, this study sought to characterize NBV infection on a broad scale. NBV was purified from cell culture supernatant and the structural proteins identified by mass spectrometry, followed by the development of anti-NBV antisera as biological tools for future assays. NBV infection in vivo was also studied by developing a disease model in Balb/c mice. Although no disease symptoms were observed, a difference in weight change between the experimental groups and the control mice as well as NBV genome isolation from multiple mouse tissues indicated an early systemic infection. NBV infection kinetics were further studied in vitro and compared between a range of cell lines, including recently-developed primary and immortalized lines derived from bat tissues. The cellular changes associated with infection were then studied using confocal and electron microscopy, which found that NBV infection induces numerous morphological changes such as disruption of the cytoskeleton and internal membranous compartments. Dispersal of the Golgi apparatus was observed in all cells except those of bat origin, which may be linked to the attenuation of Golgi function in bat-derived cells during infection. This has previously been shown as a viral immune evasion tactic. Little information is available regarding the induction of apoptosis by orthoreoviruses that cause cell membrane fusion during infection. Therefore the induction of caspase 3 during infection was measured, which showed that apoptosis is induced early during infection in bat cells compared to those of other species. This suggests that rapid apoptosis induction may play an important role during viral infection in bat cells.