Although mumps is a preventable disease, recent declines in vaccination rates have resulted in the resurgence of mumps cases. In 20-30% of post-pubescent males, the mumps virus spreads to the testes, causing mumps orchitis. This condition is characterized by painful inflammation and swelling, and ultimately leads to permanent subfertility. This illustration shows the progression of mumps orchitis from a healthy state through four sequential stages of disease. Mumps orchitis begins with swelling, followed by infiltration by immune cells (shown in blue) and hemorrhaging (blood cells shown in red). Sperm production that normally occurs inside the seminiferous tubules is arrested in late stage mumps orchitis.