The John Cunningham virus, or JC virus, is generally asymptomatic until it is triggered in people with compromised immune systems, which can then lead to a steady decline in cognitive and motor functions. Patients who experience symptoms may likely die within 9 months from onset, states Merck Manuals.
The re-activation of the JC virus, which is usually acquired during childhood, results in a rare brain infection known as progressive multifocal leukoencephalopathy, notes Merck Manuals. Classic symptoms of this disorder include worsening speech difficulties and gradual loss of muscular coordination.
The degree in which the disease progresses depends on the location of the infection. Patients with the condition may also experience visual impairment and develop dementia, a type of chronic mental illness. Although infrequent, headaches and convulsions may also manifest.