Because the passage-derived strains Asia-#8 and Asia-#9 were both able to infect CHO677 cells in addition to BHK-2P, we previously hypothesized that infection of BHK-2P cells is only possible for viruses that do not require integrins or heparan sulfate proteoglycans (HSPG) to attach to the cell surface [12]. This evidence concerns the gene CD44 and infection.