Infection of Hela cells with a virulent and an attenuated strain of pseudorabies virus studied by electron microscopy

Hollow-core particles, forming crystals in nuclei, prevailed in HeLa cells infected with an attenuated strain of pseudorabies virus (PRV). After infection with a virulent PRV strain, the cells contained mainly fully infectious dense-core particles. These findings might explain the lower susceptibility of HeLa and some other human cells to infection with attenuated strains of PRV as compared to virulent strains.