The virus is approximately 122-180 nm in diameter and is composed of a double helix of DNA which contains about 172,000 base pairs and 85 genes. The DNA is surrounded by a protein nucleocapsid. This nucleocapsid is surrounded by a tegument made of protein, which in turn is surrounded by an envelope containing both lipids and surface projections of glycoproteins which are essential to infection of the host cell
The term viral tropism refers to which cell types EBV infects. EBV can infect different cell types, including B cells and epithelial cells.
The viral three-part glycoprotein complexes of gHgL gp42 mediate B cell membrane fusion; although the two-part complexes of gHgL mediate epithelial cell membrane fusion. EBV that are made in the B cells have low numbers of gHgLgp42 complexes, because these three-part complexes interact with Human-leukocyte-antigen class II molecules present in B cells in the endoplasmic reticulum and are degraded. In contrast, EBV from epithelial cells are rich in the three-part complexes because these cells do not normally contain HLA class II molecules. As a consequence, EBV made from B cells are more infectious to epithelial cells, and EBV made from epithelial cells are more infectious to B cells. Viruses lacking the gp42 portion are able to bind to human B cells but unable to infect.