Generation of reassortants between African arenaviruses.

Lassa (LAS) and Mopeia (MOP) viruses are African arenaviruses which are carried by wild rodents and occasionally transferred to humans. In humans and nonhuman primates, Lassa causes mortality in 60% of untreated cases, whereas Mopeia does not cause mortality and has been known to protect monkeys from lethal challenge with Lassa. These two African arenaviruses also differ in their lethality for suckling outbred mice and in their plaque sizes under agar overlay. MOP virus induces small plaques and lethal infection after intracerebral (ic) inoculation. In contrast, LAS inoculation does not kill mice and the virus induces large plaques. After coinfection of Vero cells with LAS and MOP viruses some phenotypic reassortants which produced small plaques and were not lethal for outbred mice were isolated and plaque-purified. Dot-blot hybridization using LAS and MOP cDNA probes specific for L and S RNA segments revealed a genotype consisting of the L RNA of MOP and the S RNA of LAS (MOP/LAS reassortant). Adoptive transfer experiments demonstrated an ability of immune splenocytes from CBA mice intraperitoneally infected with the MOP/LAS reassortants to protect recipient mice against lethal disease after ic inoculation with LAS virus.