Tuberculosis, also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by Mycobacterium tuberculosis (MTB) bacteria. Tuberculosis initially infects the lungs, but it can also spread to other parts of the body. Most infections show no symptoms, in which case tuberculosis is considered to be inactive or latent. A small proportion of latent infections progress to active disease that, if left untreated, can be fatal. Typical symptoms of active TB are chronic cough with blood-containing mucus, fever, night sweats, and weight loss. Infection of other organs can cause a wide range of symptoms.