Tropism of Drosophila innubila Nudivirus in Cell Culture and in Tissues

Most viruses are successful because they can infect and exploit specific host tissues for reproduction and transmission. As a result, we often classify viruses by their ability to infect different tissues: respiratory, reproductive and gut, for example. Thus, knowing the tissue and cellular tropism of a virus may elucidate aspects of its biology including routes of transmission and virulence. We studied tropism of the Drosophila innubila Nudivirus (DiNV) in cells and infected hosts. DiNV is a nudivirus, a family of viruses related to the baculoviruses that are relatively large (150-200 nm), contain large double-stranded DNA genomes, and infect different host tissues. Cultured cells stained with an antibody against the DiNV nucleocapsid demonstrated punctate staining in the cytoplasm by confocal microscopy. Electron micrographs of infected cells, on the other hand demonstrated that virions are present in the nucleus. After purification, DiNV was often associated with multimembrane-like vesicles as described for Oryctes rhinoceros nudivirus. We examined tropism in hosts first by sagittal section and found most virus associated with the gut and, to a lesser extent, reproductive tissues. Upon dissection and electron microscopy, we found that DiNV in the gut is primarily in the visceral muscle of the gut and not the lumen as might be expected for a virus if transmitted fecal-orally.