Syphilitic myositis is a chronic disease caused by infection with the spirochete Borrelia in the muscles and tissues in the body. The disease can affect any muscle tissue, but most often affects the myocardium, lungs, muscles of the arms, neck, abdomen, and legs. The main source of infection is sick animals, as well as rodents, bears, panthers and other predators. Infection occurs through the bite of an infected animal, after which the bacteria enter the bloodstream and then spread throughout the body. In syphilis, bacteria trigger an immune response that leads to tissue inflammation. Symptoms of the disease include muscle pain, fatigue, muscle spasms, fever and skin rashes. Treatment involves antibiotic therapy, which can be very lengthy and difficult. In general, syphilitic myositis is a serious disease that can lead to serious complications.