Tuberculosis (วัณโรค)
Tuberculosis (TB) is caused by the gram-positive, acid-fast bacillus Mycobacterium tuberculosis. A related Mycobacterium species, Mycobacterium leprae, causes Hansen’s disease (leprosy). All
mycobacteria share acid-fast properties due to the waxy mycolic acid constituent of their cell wall. Mycolic acid allows these
organisms to retain carbol-fuchsin, a red dye, after washing in 3% hydrochloric acid in alcohol.
Mycobacterium tuberculosis is easily transmitted by the respiratory route; even normal conversation can spread the organism from person to person. At one time, TB was the most important infectious disease of humans and accounted for one-seventh of all deaths worldwide. Presently,
TB still accounts for over 1.4 million deaths per year, almost 11% of all deaths due to infectious disease. About one-third of the world’s population has been infected with
M. tuberculosis.
Primary infection typically results from inhalation of droplets containing viable M. tuberculosis bacteria from an individual
with an active pulmonary infection. The inhaled bacteria settle in the lungs and grow. The host mounts an immune response to
M. tuberculosis, resulting in a delayed-type hypersensitivity reaction and the formation of aggregates of activated macrophages, called tubercles. These are seen the x-ray images in Appendix 4.