Deletion of the UL21 gene in Pseudorabies virus results in the formation of DNA-deprived capsids: an electron microscopy studyFrans Wagenaar, Jan M.A. Pol, Niels de Wind and Tjeerd G. KimmanVet. Res., 32 1 (2001) 47-54DOI: https://doi.org/10.1051/vetres:2001108