definition of orchitis
Orchitis (or-KIE-tis) is an inflammation of one or both testicles. It is usually caused by a bacterial infection or by the mumps virus. Bacterial orchitis can be caused by sexually transmitted infections (STIs), particularly gonorrhea or chlamydia. Bacterial orchitis often results from epididymitis, an inflammation of the coiled tube (epididymis) at the back of the testicle that stores and carries sperm. In that case, it's called epididymo-orchitis.