According to Kenneth Todar, writing in the Online Textbook of Bacteriology, tuberculosis, caused by Mycobacterium tuberculosis, is the world's leading cause of bacteria-related death. Almost one out of three people worldwide are affected by tuberculosis every year. According to GlaxoSmithKline, tuberculosis kills someone every 15 seconds. Todar reports that the unique structure of Mycobacterium tuberculosis contributes to its high virulence.
Structure
Todar reports that Mycobacterium tuberculosis is a nonmotile (meaning they do not move away from the stab line) rod-shaped bacteria. The common site of infection is the lungs because the bacteria are obligate aerobes, meaning that they require oxygen. The cell wall of Mycobacterium tuberculosis is mostly lipid (along with peptidoglycan, a polymer commonly found in the cell walls of bacteria); the high amount of lipids in the cell wall contributes to difficulties in staining and dyeing the bacteria. The bacterium is difficult to kill because it is resistant to antibiotics and other treatments.
Routes of Transmission
According to the Centers for Disease Control and Preventions, tuberculosis is spread when infected people cough, sneeze and speak and others breathe the bacteria in. The CDC reports that tuberculosis is not spread by such means as hand shaking, sharing utensils, touching belongings or even by sharing toothbrushes and kissing.
Diagnosis
A skin test is performed to determine whether someone has been infected with tuberculosis. According to the CDC, a substance called tuberculin is injected into the arm and is then monitored for reaction. To confirm the presence of tuberculosis disease, health care workers will culture a sputum sample and do a chest X-ray. The CDC also reports that there are blood tests for tuberculosis, but these are not widely available.
Effects
Even when a person becomes infected with Mycobacterium tuberculosis, she may not necessarily become ill. This is called latent infection, and these people, according to the CDC, cannot infect other people but will test positive to a skin test. People who are infected but do not have tuberculosis disease may develop it later, especially if the immune system becomes weakened. HIV-positive people are susceptible to tuberculosis disease, and, according to Todar, Mycobacterium avium, a related bacterium, also causes tuberculosis-like illness in HIV-positive people. When tuberculosis does cause illness, it causes a severe and long-lasting cough that produces blood and sputum along with chest pain. Other symptoms, according to the CDC include weakness, fatigue, lack of appetite, chills and fever and night sweats.
Vaccination and Treatment
According to the CDC, bacille Calmette-Guérin is used as an immunization against tuberculosis in countries with high tuberculosis prevalence. It is not generally used in the United States. Being immunized against tuberculosis may cause people to test positive on a skin test. The CDC reports that for people with latent TB infection, a drug called INH is prescribed to prevent the development of symptoms. A course of treatment may take nine months or more, depending on the patient's age and immune health. Multidrug treatment is used in people with active tuberculosis disease.
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