When your immune system is strong, the JC virus, a common polyomavirus that infects most adults without causing symptoms. Also known as John Cunningham virus, it usually stays quiet in your kidneys and bone marrow. But if your immunity drops — from disease, aging, or long-term drugs — this harmless virus can wake up and attack your brain. That’s when things get dangerous.
The result is progressive multifocal leukoencephalopathy, a rare but fatal brain disease caused by JC virus reactivation. It doesn’t spread from person to person. Instead, it’s your own virus turning traitor. PML destroys the white matter in your brain, leading to weakness, vision loss, speech problems, and confusion. It’s not cancer. It’s not an infection you catch. It’s your body’s defense system failing to keep a silent guest under control.
People on long-term immunosuppression, medications that dampen the immune system to treat autoimmune or transplant conditions are most at risk. Drugs like natalizumab, rituximab, and even some biologics used for MS or rheumatoid arthritis have been linked to PML. The risk isn’t high — but when it happens, it’s often too late. That’s why doctors test for JC virus antibodies before starting these treatments. Knowing your status can save your life.
There’s no cure for PML. Stopping the drug that triggered it is the only real option — but even then, recovery isn’t guaranteed. Some people stabilize. Others don’t. That’s why awareness matters. If you’re on an immunosuppressant and suddenly feel off — trouble walking, blurred vision, slurred speech — don’t wait. Get checked. PML moves fast, and early detection gives you the best shot.
This collection of articles doesn’t just list facts. It connects the dots between what you’re taking, how your immune system responds, and the hidden risks that don’t show up on routine blood tests. You’ll find real-world insights on how drugs like those used for MS, rheumatoid arthritis, and even HIV treatment can open the door for JC virus to strike. You’ll see how monitoring, testing, and timing make all the difference. And you’ll learn what to ask your doctor before starting or switching any therapy that affects your immunity.
Below, you’ll find detailed guides on drug interactions, immune system effects, and safety protocols that could help you avoid the worst-case scenario. This isn’t theoretical. These are the stories behind the warnings on your prescription label — and the facts you need to stay safe.
PML is a rare but deadly brain infection triggered by immunosuppressants like natalizumab. Learn the real risk factors, how to detect it early, and what steps can save your life.