Hidden Threat of a Common Virus

There’s a lesser-known virus that might infect up to 90 percent of the population, lingering unnoticed in our cells for life. However, if it gets activated, it can have devastating effects on the brain. Recently, researchers have reported the potential for this virus’s activation to be triggered by factors affecting about 10 percent of adults globally.

The virus in question is human polyomavirus 2, often referred to as the JC virus or John Cunningham virus. It got its name from the unfortunate patient from whom it was isolated back in 1971. This virus can be found in the urine and stool of those infected and is transmitted via the fecal-oral route. Many individuals are believed to contract it early in life, with studies indicating that roughly 50 to 90 percent of adults have encountered it at some point.

Researchers think that the tonsils or possibly the gastrointestinal tract could be the initial sites of infection. However, this first encounter is typically asymptomatic. During this phase, the person is said to be infected with what’s known as the archetype JC virus, which sets up a silent, ongoing infection that lasts a lifetime.

For most people, this JC virus infection remains inconspicuous. Unfortunately, for a small fraction, it may become reactivated, altering its genetic makeup and transforming into a significant threat known as progressive multifocal leukoencephalopathy (PML).

PML: A Serious Consequence

In cases of PML, the newly active virus infiltrates the brain, destroying specific brain cells, particularly those that create myelin sheaths, essential for nerve protection. This results in widespread demyelination, leading to nerve cell malfunction and death. Imaging can reveal distinctive lesions in the brain that help in diagnosing PML, alongside the detection of JC virus DNA in cerebrospinal fluid. The symptoms of PML can be misleading, resembling those of a stroke or multiple sclerosis, including issues with speech, vision, motor skills, and seizures.

PML was first recognized in 1958 in a patient suffering from cancer and was deemed quite rare until the 1980s, when it started occurring more frequently in individuals with HIV/AIDS. PML eventually became associated with AIDS, affecting about 2 to 5 percent of HIV-positive patients during the initial stages of the epidemic. This condition was typically fatal until the advent of highly active antiretroviral therapy (HAART) in 1996, which diminished the number of cases, making it less deadly, although survivors often endure significant long-term damage.