A progressive neurological disorder affecting 10 million people globally, Parkinson’s can cause disruptive symptoms such as tremors, immobility and loss of balance. Now, scientists at Northwestern Medicine have discovered that a usually harmless virus — the Human Pegivirus — may be a contributor to the disease.

Parkinson's disease occurs when brain cells that produce an important hormone called dopamine begin to die off or become impaired. As dopamine levels decrease, people develop movement symptoms like shaking or stiffness, as well as problems maintaining balance and coordination.

Parkinson's disease is a neurogenerative disease that affects more than 1 million people in the U.S. While some cases are caused by genetics, the cause is unknown in most.