After my last relapse, my doctor wants me to get tested for the JC virus. Can someone explain to me what is the JC virus?
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The JC virus is a common infection completely unrelated to MS. About half of the population have been infected by the virus and it is normally kept under control by the immune system causing no problems. If the immune system is weakened and the body is less able to fight an infection, the virus can reactivate and cause serious and potentially fatal inflammation and damage to the brain known as progressive multifocal leukoencephalopathy (PML).
Treatment with some of the disease modifying drugs, in particular Tysabri, can increase the risk of developing PML.