Actinomycosis is usually caused by bacterium called Actinomyces israelii. This is a common and organism found in the nose and throat. It normally does not cause disease.
Because of the bacteria's normal location in the nose and throat, actinomycosis most commonly affects the face and neck. The infection can sometimes occur in the chest (pulmonary actinomycosis), abdomen, pelvis, or other areas of the body. The infection is not contagious. This means it does not spread to other persons.
Symptoms occur when the bacteria enter the tissues of the face after trauma, surgery, or infection. Common triggers include dental abscess or oral surgery. The infection can also affect certain women who have had an intrauterine device (IUD) to prevent pregnancy.
Once in the tissue, the bacteria causes an abscess, producing a hard, red to reddish-purple lump, often on the jaw, from which comes the condition's common name, "lumpy jaw."
Eventually, the abscess breaks through the skin surface to produce a draining sinus tract.