Plasticity of Phenotypic Characters of Rabies-Related Viroses: Spontaneous Variation in the Plaque Morphology, Virulence, and Temperature-Sensitivity Characters of Serially Propagated Lagos Bat and Mokola Viruses

Abstract

Rabies-related Mokola and Lagos bat rhabdoviruses produced heterogeneous plaque populations after growth in BHK/21 cells. Three plaque clones of each virus differed in plaque morphology, pathogenicity for mice, capacity for replication at elevated temperatures of incubation, and degree of inactivation by antiserum to rabies virus. Although each type of clone was thrice clone-purified, certain clones continued to produce diverse types of plaques; further selection of plaque variants revealed continuous spontaneous alteration of several phenotypic characters. Two Mokola clones yielded subclones of widely diverse plaque morphology; nonpathogenic clone no. 1 yielded both pathogenic and nonpathogenic plaque variants. Mouse-pathogenic Lagos clone no. 3 also yielded subclones differing widely in plaque morphology and temperature sensitivity. Several subclones of Lagos clone no. 3 were either apathogenic for mice or different from the parental virus in length of incubation period in vivo or in dose-response pattern of the death curve. All subclones of Lagos and Mokola virus retained antigens that cross-reacted with antiserum to rabies virus. Attempts to select or induce variants that did not react with rabies antiserum were unsuccessful.