Isolation of a cytomegalovirus-like agent from wild rats

In 8 of 10 wild rats trapped in The Netherlands, an infectious viruslike agent was isolated predominantly from the salivary glands and could be serially passed in laboratory rats. In rat embryo cells a typical cytomegalo-like cytopathic effect was produced. The morphologic and cultural characteristics of the isolated agent were comparable with those of the mouse cytomegalovirus (MCMV). The virus-nucleocapsid had a size of 92 nm and was not ether-resistant. The extracellular nucleocapsids were often enclosed by an outer layer of very variable shape and size. The formation of Fc receptors on cells infected with the rat virus could be demonstrated. The wild rats possessed neutralizing antibodies to the isolated agent. The rat agent grew only in rat embryo fibroblast cells while MCMV grew in rat and mouse embryo cells. The rat agent gave plaques in REF monolayers. Electron microscope studies showed the presence of nucleocapsids in the nucleus.