Pretty much every disease modifying therapy (DMT) on the market right now has a risk of “PML” if you are JCV positive, so just what does that actually mean? When I was first diagnosed I was on Tysabri and my JCV number had to be checked every three months because the risk of PML was high on that medication. All the medications I have been on and that have come on the market since 2014 have a risk of PML, some more than others.

When I was on my first DMT I just read about PML and it scared the shit out of me, no cure and terrible side effects. So what are these two things exactly? “John Cunningham virus, is a common germ. More than half of all adults have been exposed to it.” – WebMD OK, so not a big deal if more than half of all adults have been exposed to it, just like Epstein–Barr virus, most people have been exposed to this at some point. All people with MS have had Epstein–Barr virus, but not all people who have had Epstein–Barr virus get MS.

JC virus is also known at Human polyomavirus 2, causing progressive multifocal leukoencephalopathy (PML) in those who take drugs for immunosuppression. Scientists who found it changed it JC virus after the initials of the person they related the virus to PML. Once you have JCV it sheds in multiple portions of your body and is able to cross the blood brain barrier where it infects oligodendrocytes and astrocytes. These are important parts of the brain that are impacted by MS. In healthy individuals the virus is dormant and sheds but causes no real danger. Once you introduce an immune suppressing medication it reactivates the virus.

“Experts don’t know how it’s spread, but it’s thought that many people pick it up as kids through food or water that has the virus in it. It settles in your urinary tract, bone marrow, tonsils, or brain. It can stay there for years, and most people never know they have it.” Indicated in this article. A blood test can easily tell you if you have JCV or not, which thankfully I am still negative. If you are positive, depending on the number the doctor will change your medication if the risk out ways the benefits.

Both MS and PML are demyelinating diseases, the difference is PML moves quickly and can cause serious brain damage or death. This article in Every Day Health states “The incidence of PML has historically been quite low, and then there was an “incredible” increase of PML with the introduction of Tysabri, implying that the drug does more than cause immunosuppression. It favors the development of a neurotropic virus, or a virus that tends to attack the nervous system, Cortese says.”

The higher amount of JCV antibodies in your system the greater your risk of developing PML. With each DMT for MS the risk varies, and with some of them the risk is caused by a drop in the number of lymphocytes as opposed to an opportunal virus invading the central nervous system.

So the JC virus has unknown means of transmission but a large portion of the population have it already, sitting dormant in organs of the body. Only when you have a condition requiring immune suppressing medications is when you should think about it. If you are on these types of medications for MS, RA, leukemia, lymphoma or organ transplants your doctor has most likely already had this conversation with you.

Sources: https://www.webmd.com/brain/jc-virus#1, https://en.wikipedia.org/wiki/Human_polyomavirus_2, https://www.sciencedirect.com/topics/neuroscience/jc-virus, https://www.everydayhealth.com/multiple-sclerosis/treatment/jc-virus-ms-what-you-need-know/,