DefinitionOrchitis is swelling (inflammation) of one or both of the testicles.Alternative NamesEpididymo-orchitis; Testis infectionCauses, incidence, and risk factorsOrchitis may be caused by an infection from many different types of bacteria and viruses. It is usually a result of epididymitis, inflammation of the tube that connects the vas deferens and the testicle.The most common virus that causes orchitis is mumps. It most often occurs in boys after puberty, and is rare before the age of 10. Orchitis usually develops 4 - 6 days after the mumps. Some boys who get orchitis caused by mumps will have shrinking of the testicles (testicular atrophy).Orchitis can develop in men with the rare disease, brucellosis.Orchitis may also occur along with infections of the prostate or epididymis. It ma