Alterations in plaque size, virulence, and lipid content of Venezuelan equine encephalomyelitis VEE virus were examined for possible interrelationships among these properties during 10 serial passages in embryonated eggs, suckling mice, chick embryo fibroblasts, and L cells. The chick embryo host maintained the same large-plaque and virulence properties of the virus through 10 passages as seen in the original seed. Passage of virus in either L cells or chick fibroblasts rapidly produced populations that were, in the main, intermediate with respect to plaque size and virulence. Passage of virus in suckling mouse brain yielded populations that were intermediate with respect to plaque size only. The nature of the lipid of the virus, in terms of the ratio of petroleum ether-soluble to-insoluble lipid, changed after only one passage in all systems except in chick embryos. Nine additional serial passages failed to enhance these changes in viral lipid, suggesting that the decrease in the large-plaque and virulence properties was not directly associated with changes in lipid content.
Availability: Published in Journal of Bacteriology v91 n6 p2343-8 Jun 1966.