There’s a virus you’ve never heard of that’s estimated to infect up to 90 percent of people and lurk quietly in your cells for life, but if activated, it will destroy your brain. If that’s not surprising enough, researchers reported this week It may be a new way for the virus to become active – it affects up to 10 percent of adults worldwide.
The virus is human polyomavirus 2, also called JC virus or John Cunningham virus, named after the poor patient from whom it was first isolated in 1971. It manifests itself in the urine and feces of infected people and is spread through the fecal-oral route. Many people are thought to be infected early in life, and blood test surveys have suggested this 50-90 percent of adults exposed at once.
Researchers hypothesize that the primary site of infection is the tonsils or possibly the gastrointestinal tract. However, wherever it occurs, the primary infection is asymptomatic. At this point, a person becomes infected with what is called archetype JC virusquietly establishing a persistent but completely silent lifelong infection.
For the vast majority of people, their JC virus infection will be silent. But for an unlucky few, the JC virus will wake up, rearrange its genetic material, and become a brain-destroying nightmare that causes a disease called progressive multifocal leukoencephalopathy or PML.
Devastating disease
In PML, the new disease-causing virus, or “PML-like” JC virus, actively invades the brain and attacks specific brain cells, including cells forms insulating myelin sheaths that protect nerve cells. This leads to extensive demyelination, resulting in nerve cell dysfunction and death. On imaging, PML can appear as signature lesions in the brain. These described lesions combined with test findings of JC virus DNA in the cerebrospinal fluid is how PML is diagnosed. But for patients experiencing PML, symptoms can mimic anything from a stroke to multiple sclerosis, causing problems such as speech disorders, visual impairments, motor dysfunctions and seizures.
PML was first discovered in 1958 in a cancer patient. But it was considered extremely rare until the 1980s, when it began to be seen in patients with HIV/AIDS. In fact, PML has become an AIDS-defining disease, with 2 to 5 percent of HIV-infected patients developing it early in the epidemic. The situation then was just as deadly. But with the introduction of highly active antiretroviral therapy (HAART) in 1996, the incidence of PML decreased and the disease was no longer a death sentence, although survivors often have significant permanent damage.
