Orchitis may be caused by an infection from many different types of bacteria and viruses. The most common virus that causes orchitis is mumps. It most often occurs in boys after puberty. Orchitis usually develops 4 – 6 days after the mumps begins. Because of childhood vaccinations, mumps is now rare in the United States. Dr. Carlo Oller Board Certified Emergency Physician Please visit my website, www.DrER.tv make sure you subscribe, comment, and share! That is the best way to show your support.