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Epstein-Barr virus

Epstein-Barr virus is a form of human herpesvirus. Most people have been infected with it at some point in their lives – in the US, 90–95% of adults have evidence of having had it before and half of all five-year-olds. When contracted in childhood, EBV generally causes no symptoms or no symptoms distinguishable from the myriad colds that children constantly get. If you have never had it before and contract it in adolescence, however, there is a 35–50% chance that it causes glandular fever (also known in the US as “mono”).

In 2022, it was shown that a recent EBV infection makes you 32x more likely to develop multiple sclerosis. A subsequent study offered a possible explanation: Some multiple-sclerosis patients have antibodies that bind both an EBV protein and a protein in the brain, which is erroneously targeted by the immune system in multiple sclerosis.

EBV has also been implicated in a number of types of cancer(external link). The virus hijacks the immune system’s B cells, making them not get culled as per usual but persist as “memory cells” (and replicate). If the cell is also abnormal in some other kind of way, this can cause cancer. For example, Burkitt’s lymphoma was observed from the 1960s to develop in children who’d contracted malaria as well as EBV.

People with conditions ranging from lupus, rheumatoid arthritis and chronic fatigue syndrome also have higher-than-normal levels of EBV antibodies, on average. It seems like there’s some mechanism which is not fully understood whereby a latent EBV infection (remember, 95% of people have it…) can cause further illness – but we don’t know why this happens in some people but not most.