Replication and release of epizootic haemorrhagic disease virus in BHK-21 cells

Epizootic haemorrhagic disease virus (EHDV) was seen by light and electron microscopy to replicate in perinuclear locations. Tubules, paracrystals and virus matrices were associated with replication sites. As infection proceeded, aggregates of virus migrated towards the cell periphery, resulting in cell membrane rupture near the virus aggregate with the subsequent release of the virus aggregates. Virus release, as seen by light microscopy, gave the appearance of occurring by a 'budding' process whereby part of the cell would swell and subsequently rupture or break away. Infectivity studies indicated that approx. 80% of newly replicated virus was released extracellularly in aggregates which required disruption to maximize infectious virus yield. Trypsin did not enhance virus infectivity. Of the six EHDV isolates used in this study each isolate was characterized by its own maximum yield obtained after several serial passages in cell culture.