Printed in Great Britain Simian Haemorrhagic Fever (SHF): New Virus Isolate from a Chronically Infected Patas Monkey

A new strain of simian haemorrhagic fever (SHF) virus was isolated from chron-ically infected patas monkey no. 248 (P-248) in USU-Io4 cells. The P-248 isolate had the same size, morphology and cytoplasmic site of replication as the prototype LVR strain. However, the P-248 isolate caused a persistent infection without noticeable cytopathology in USU-Io 4 cells rather than the strongly lytic infection produced by prototype LVR virus. The capacity of P-248 virus to produce a persistent, non-lyric infection of USU-Io 4 cells was a very stable characteristic of the isolate. Extensive serial passage of this isolate through USU-Io 4 cells (over 5o passages) and rhesus monkeys (six passages) failed to unmask virus with lytic properties for USU-Io 4 cells. Culture medium from persistently infected cultures a sayed in rhesus monkey peritoneal mononuclear phagocytes, where measurable cytopath-ology occurs, was found to contain about IO 5 to Io 6 TCIDs0/ml of cell-free P-248 virus. ImmunolabeUing techniques howed only a tow percentage of infected cells in persistently infected cultures. The mechanism of persistence of the P-248 isolate in USU-Io4 cells has not been determined but evidence suggests it does not involve interferon r defective interfering particles