Epstein-Barr Virus (HHV-4) has a dual cell tropism for human B-lymphocytes (generally non-productive infection) and epithelial cells (productive infection). There is no suitable animal host, but replication/latency has been studied extensively in transformed human cell lines. HHV-4 is widespread worldwide, with ~75% of adults infected.
An open reading frame or ORF is a portion of an organism's genome which contains a sequence of bases that could potentially encode a protein. In a gene, ORFs are located between the start-code sequence (initiation codon) and the stop-code sequence (termination codon).