Evolution of in vitro persistence of two strains of canine parainfluenza virus. Brief report.

Lytic stock virus (CPI+) exhibited prominent CPE in Vero cell monolayers. The non-syncytial giant cell forming strain (CPI-) was isolated from brain tissues of a dog after experimental infection with syncytial giant cell-forming (CPI+) virus. In mixed infection experiments, CPI(-) virus interfered with the replication of CPI(+) virus in that simultaneously infected cells showed strand-forming CPE typical of CPI(-) and reduction of CPI(+) yield. The CPI(-) virus established immediate in vitro persistence, followed by a severe crisis at passage (p) 8 and several similar crises until p 31; no further crises occurred throughout the remaining observation period (p 80). The CPI(+) did not establish immediate in vitro viral persistence and experienced several lytic crises until p 29. No further crises were observed throughout the observation period (p 100).