Most adults carry a lifelong virus now tied to multiple sclerosis
About 90% of American adults show signs of past infection with Epstein–Barr virus, usually picked up through saliva and never noticed. It hides in memory B cells for life. It was the first virus found to cause cancer, and a 20-year study of 10 million US service members linked recent infection to a 32-fold jump in MS risk.
Epstein–Barr, also called human herpesvirus 4, is one of nine herpesviruses that infect people. Its DNA genome of about 172,000 base pairs carries 85 genes inside a particle 122–180 nanometres across. Children often catch it early, around half of US five-year-olds already have, and usually shrug it off with no or mild symptoms. Catch it as a teenager or young adult and there is a 35 to 50% chance of infectious mononucleosis, the glandular fever of exhaustion, fever, sore throat and swollen glands; EBV causes about 90% of such cases.
Its trick is shifting between two modes. In the lytic phase it copies itself and floods the body with new particles. In latency its circular genome sits quietly in the nucleus and only a handful of genes stay switched on. Inside B cells it moves through three latency programmes: the first turns a resting cell into a dividing blast, the next nudges it to become a memory cell, and the last keeps just enough activity for the viral genome to be copied whenever the cell divides. In the lab, infected B cells become immortal lines that grow indefinitely, which shows how the virus can drive cancer. Stress hormones called glucocorticoids have been shown to reactivate it.
Its entry methods are clever. To enter B cells a surface protein, gp350, latches onto the receptor CD21; epithelial cells are entered by a different route that gp42 actually hinders. As a result, virus made in B cells is better at infecting epithelial cells, and vice versa, so it can ping-pong between tissues.
The disease list is long: Burkitt and Hodgkin lymphomas, nasopharyngeal and gastric cancers, and possibly higher risks of lupus and rheumatoid arthritis. Around 200,000 cancers a year worldwide are attributed to it. No vaccine tested so far has prevented infection, and researchers still struggle with models: 2D cell lines lack realism, and humanised mice and tree shrews bring species limits of their own.
Source: Epstein–Barr virus
