An antigenically distinct member of the herpesvirus group of viruses, whose genome is deoxyribonucleic acid (DNA). Under electron-microscopic observation, the mature virus is indistinguishable in size and structure from the other human herpesviruses; that is, it has a nucleocapsid about110 nanometers in diameter, and when an envelope is present, the particle diameter is about 180 nm. The 78-nm central core, which is often observed in other herpesviruses, is not clearly visible in Epstein-Barr (EB) particles within infected cells, and few of the intracellular particles possess an envelope. Only about 10% of the extracellular virus particles are enveloped.