Pathogenicity of equine herpesvirus: in vivo persistence in equine tissue macrophages of herpesviuus type 2 detected in monolayer macrophage cell culture.

Equine macrophages from the mammary glands of a yearling filly and an 18-year-old barren nonlactatind mare formed cell monolayers in continuous cultures. There was absence of viral cytopathic effect (CPE) in early cell culture passages. The cells from the early cell culture passages having no CPE failed to show evidence of virus or viral antigen by electron microscopic and immunofluorescence studies. Foci of CPE first appeared in the monolayer cell cultures from the filly and the mare in the 3rd and the 4th serial passages respectively, and the CPE increased on subsequent serial passages. Equine herpesvirus type 2 (EHV 2) cultures showing CPE. The macrophage monolayer culture established from the mare produced CPE foci more consistently than did the culture from the filly, and they were more numerous. Conversely, the peripheral blood mononuclear cells from the filly on cocultivation with an equine embryo kidney monolayer cell culture produced more EHV 2 CPE foci than did those from the mare. This study indicated that tissue macrophages may be a site for latent and persistent herpesvirus infections in horses.