What Is JC Virus? (2024)

John Cunningham virus or JC virus is another name for human polyomavirus 2. JC virus is very common—between 50% to 90% of the world’s population would test positive for it.

For most healthy people, JC virus will not cause problems. The virus becomes inactive (dormant), and most people will never get sick from it—or even know that they carry it. However, people with weak immune systems are at risk of developing a serious, potentially fatal, illness if they get JC virus.

This article will go over what JC virus is. You'll learn about the symptoms of JC virus, how it's diagnosed, and how JC virus is treated.

What Is JC Virus?

The JC virus is a type of polyomavirus, a family of viruses that primarily infect mammals and birds. This virus is very common around the world and often causes no symptoms. It's easily passed on among people in close contact, such as from a parent to a child.

JC virus is most often found in the tonsils, but can also be in the gastrointestinal tract or kidneys. Unlike other germs, the JC virus can cross the blood-brain barrier.

While researchers are not exactly sure how it works, they know that once JC virus gets into the brain it infects the cells that make the protective coating on nerves (myelin). Without the covering, nerves lose their protection (demyelination) and the brain gets damaged.

JC Virus and PML

When JC virus gets into the brain, the biggest concern is that a person will develop a rare and potentially fatal disease called progressive multifocal leukoencephalopathy (PML).

PML causes severe and fast-moving damage to the white matter in the brain. Of people diagnosed with PML, 30% to 50% die within the first few months. Many people who survive have a lasting neurological disability.

Symptoms

In healthy people, the JC virus does not cause symptoms because it is not active. However, if it gets reactivated in a person with lowered immunity, PML develops and damages different parts of the body—usually the brain.

The symptoms related to JC virus and PML depend on where the damage is but can include:

• Weakness
• Clumsiness
• Having a hard time thinking
• Trouble talking or being unable to speak
• New problems with eyesight or loss of vision
• Loss of feeling in or difficulty moving your limbs
• Dementia-like symptoms and personality changes
• Seizures
• Headaches (more common in people who have HIV/AIDS)

The symptoms of PML may not start all at the same time. While they can come on gradually, the symptoms tend to get worse quickly once they start. It usually does not take long before a person becomes so sick they cannot get out of bed.

PML can cause death as soon as a month after someone gets sick if they don't get treatment, but some people may live up to a year or rarely two.

How Do You Get JC Virus?

Most people are exposed to it during childhood, particularly within their families. Research has shown that members of the same familiar tend to carry similar, if not the same, strains of JC virus. Because it is easily passed on among people in close contact, parents passing it to their children is thought to be one of the most frequent ways that JC virus is spread.

When JC virus is in the kidneys, it can come out with urine and spread to other people who come into contact with it. Most healthy people will not have any symptoms of an infection and probably won’t realize they’ve been exposed to JC virus.

Once the virus gets inside someone’s body, it stays there but isn’t doing anything that could cause illness (dormant). It’s only if something reactivates the JC virus that a person can get sick.

Risk Factors for JC Virus

Some factors increase the risk of JC virus becoming active again, including:

• A person's immune system is weak because they have diseases like cancer or HIV/AIDS
• A person is taking drugs to suppress their immune system because they have an autoimmune disease or they received an organ transplant

People with weak immune systems are more at risk for many types of infections, including one caused by JC virus. The risk of exposure can occur at any time because JC virus is so common.

If someone is at high risk for infection from JC virus (such as those who start medication that puts them at risk) they will need to have repeated tests to check for it even if they tested negative before.

JC Virus: Does Having MS Increase Your Risk for PML?

Having a weak immune system or taking certain medications that quiet it can also increase a person's risk of getting PML from JC virus.

One condition that's linked to this risk is multiple sclerosis (MS), mostly because of the medications used to treat the condition.

People with MS already have areas of damage (lesions) in their nervous system, including in their brains. MS is usually treated with medications that try to stop the immune system from attacking the body and causing the lesions to develop.

The Food and Drug Administration (FDA) has identified several drugs used to treat MS as having the potential to increase a person’s risk of PML, including:

• Gilenya (fingolimod)
• Tysabri (natalizumab)
• Novantrone (Mitoxantrone)
• Tecfidera (dimethyl fumarate)

Special drugs given to people who need organ transplants to prevent rejection may also increase the risk of PML, including:

• Imuran (azathioprine)
• CellCept (mycophenolate mofetil)

Other drugs used to treat autoimmune diseases have been associated with an increased risk of PML, including:

• Methotrexate
• Corticosteroids
• Cyclophosphamide

How Is JC Virus Diagnosed?

There are a few ways providers can diagnose JC virus and PML, from blood tests to brain biopsies.

Blood Tests

Your provider can order a special blood test to find out if you have JC virus antibodies.

If the test shows the virus is in your body, it does not mean you will definitely get PML. Your provider will monitor you for signs of illness or any additional factors that could increase your risk, such as a new medication you're taking.

Spinal Taps

If you are having symptoms that could be related to JC virus, your provider might want to do other tests, such as a spinal tap (lumbar puncture). Your provider can do a special test called a PCR to look for DNA from the JC virus in your spinal fluid.

Imaging tests like an MRI or a CT scan can help your provider see into your brain, kidneys, or other organs. If the JC virus is active, they might see lesions in places where it has caused damage.

If you start showing signs of PML, your provider might need to take a sample of tissue from your brain (biopsy) to check for JC virus, but it's usually not needed to make the diagnosis.

Can JC Virus Be Treated?

There is no way to cure JC virus or PML if it develops. However, there are some ways that providers can try to treat it and give a person the best chance at recovery.

If you take medication to suppress your immune system, such as steroids, your provider will want you to stop taking them. Depending on why you were taking these medications, you may need to be closely monitored by your medical team.

Stopping these drugs comes with risks. Your provider will compare these risks to the risk of getting PML.

For persons with HIV infection, it is important to initiate or optimize effective antiretroviral therapy (ART).

Will Stopping My Medications Cure JC Virus?

Sometimes, people with PML start to feel better once they stop these medications—though JC virus can keep doing damage. Any damage to the brain that has already happened may not heal.

People with conditions such as HIV/AIDS are more likely to have long-term complications from JC virus and PML and may have different symptoms, such as a headache.

Other people do not feel better when they stop taking medication and may even feel worse. This is because, without the drugs to calm down their immune system, the body mounts a major response against any virus—including the JC virus.

This response can make a person's symptoms more intense. If this happens to you, your provider may prescribe other medications or treatments to help you feel better and prevent complications such as brain swelling.

If you have been taking medications such as Tysabri, your provider will want to do a procedure to help flush the drug out of your system as quickly as possible.

Plasma exchange helps clear the medicine from your body and allows your immune system to try to fight JC virus on its own. You may need to have more than one plasma exchange to make sure all the medication is out of your body.

Summary

JC virus is very common and won't make most healthy people sick. However, there are people who are more likely to get sick if they are exposed to JC virus. Having JC virus in your body as well as other risk factors can increase your chances of getting a very serious brain condition called PML, but it does not mean that you will definitely get sick.

There is no cure for PML and many people who develop it will die soon after they get sick. That's why it is very important that people who are at risk are closely monitored by their healthcare team.When it's caught early, PML can be treated and some people do recover, though they may have long-term neurological symptoms.

The treatment for JC virus usually involves stopping any medications that can increase a person’s risk for PML, such as those used to treat multiple sclerosis (MS) and other autoimmune conditions.If you take a medication that increases your risk for PML, your provider may regularly test you for JC virus antibodies.