Tuberculosis

Origins

TB is an ancient disease dating back to at least 4500 b.c.e. based on skeletal evidence from Neolithic Germany. The spines of Egyptian mummies indicated TB infection dating back to 3000 b.c.e. Through the centuries, many have speculated on the causes of TB. The first medical report of TB is credited to Hippocrates (460–370 b.c.e.), who called it phthisis (Greek for “consumption”). In 1882, German physician Robert Koch discovered the bacteria responsible for most types of tuberculosis (Mycobacterium tuberculosis). In 1905, Koch won the Nobel Prize for this discovery. Koch assumed bovine and human TB were different, but scientists later proved otherwise, and milk has since been pasteurized to remove one of the key infection routes by which humans acquired TB.

Classification

The Centers for Disease Control and Prevention (CDC) classifies Mycobacterium tuberculosis at biosafety level three. It is considered a serious or potentially deadly disease after inhalation and requires specific safety equipment and procedures when handling the infectious agent. TB is listed as ICD-9 010-018. The eight listed ICD-9 are 010 (primary TB infection), 011 (pulmonary TB), 012 (other respiratory TB), 013 (TB of meninges and CNS), 014 (TB of intestines, peritoneum, and mesenteric glands), 015 (TB of bones and joints), 016 (TB of genitourinary system), 017 (TB of other organs), and 018 (military TB).

The TB bacterium is Mycobacterium genus belonging to the family Mycobacteriaceae and consists of lots of species, with some being pathogenic to humans. The mycobacteria are small rod-shaped species of bacillus, which are classified into three groups for diagnosis/treatment purposes. The first group is mycobacterium tuberculosis complex (MTBC), which can cause tuberculosis in humans and animals, such as M. tuberculosis, M. bovis, M. microti, M. africanum (an opportunistic infection in HIV+ patients), M. canettii (rare), and M. caprae (rare). The second is M. leprae, which causes leprosy. The third group is nontuberculous mycobacteria (NTM), which do not cause TB or leprosy but can cause pulmonary disease that resembles TB and causes inflammation of lymph nodes (lymphadenitis), skin disease, or disseminated disease. Another M. genus is Mycobacterium avium, which causes a TB-like disease common among AIDS patients, and the paratuberculosis species causes Crohn's disease.

Transmission

Active and untreated TB of the lungs is contagious and can spread to others by the uninfected inhaling the species of bacillus through the aerosolization (i.e., the person speaks, coughs, sneezes, laughs) of tiny droplets from an infected person. TB can remain in the air for several hours. Even though TB is contagious, it is not easy to acquire because it is dependent on duration of exposure, ventilation, frequency of aerosolizations, and pathogenicity of the strain. It is difficult to acquire TB from casual interactions, such as sharing drinking glasses or conversations. Commonly, TB infection requires regular and prolonged close contact with a contagious person before becoming infected, such as from a coworker or living or residing in the same place.

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