Tuberculosis

Tuberculosis is a chronic infectious disease caused by the Mycobacterium tuberculosis complex, affecting multiple organ systems; the lung is the most common site, accounting for 80-90% of all organ TB. It can also affect the liver, kidney, brain, and lymph nodes. Main transmission routes are respiratory, digestive, cutaneous, and uterine, but respiratory predominates. When sputum dries from pulmonary TB patients, bacilli spread with dust and are inhaled. Whether inhaled droplet nuclei cause disease depends on the number, virulence, and host resistance. Treatment should begin immediately upon diagnosis.

Common Symptoms

Chest pain; dyspnea; anorexia; hemoptysis; night sweats; low fever; fatigue; low-grade fever; amenorrhea; persistent low fever

Causes and Pathogenesis

The M. tuberculosis complex includes M. tuberculosis, M. bovis, M. africanum, and M. microti; M. tuberculosis causes most human disease. It is 0.3-0.6 µm × 1-4 µm, slender and slightly curved with rounded ends. Acid-fast staining is a key feature; acid-fast bacilli in specimens most often represent M. tuberculosis but require culture and speciation. It grows slowly, taking 2-4 weeks for visible colonies. The cell wall is ~60% lipid, mainly mycolic acid and cord factor; the former underlies acid-fastness, while trehalose dimycolate and sulfatide mediate granuloma formation and intracellular survival. Lipoarabinomannan is highly immunogenic and widely used in serology. Pathogenesis: After phagocytosis by macrophages, the host immune response determines disease. (1) Natural history: Tuberculin skin test converts 3-8 weeks after infection; 95% of healthy infected persons have spontaneous resolution of the primary complex, becoming latently infected; about 5% later develop disease from reactivation. (2) Host response: Inhaled bacilli are phagocytosed by alveolar macrophages forming early foci; initial intracellular growth forms central solid caseous necrosis that limits replication. T-cell-mediated cellular immunity and delayed-type hypersensitivity develop, decisively influencing outcome. During commensalism, bacilli persist within fibro-encapsulated caseous centers. Caseous foci contain viable but non-replicating bacilli; once liquefied, they provide an ideal environment for proliferation.

Treatment

Drug therapy, supportive therapy

Preventive Measures

BCG vaccination. Since TB is mainly airborne, controlling air pollution is key. Measures: 1. Good hygiene: TB patients should cover coughs with a handkerchief, spit sputum into paper and burn it; sputum cups should soak in 2% cresol soap or 1% formalin for ~2 hours. Tubercle bacilli are most susceptible to moist heat; boiling kills them in 15 minutes. Boil clothes and handkerchiefs before washing. 70% alcohol is most effective for daily disinfection (15-30 seconds). Milk must be pasteurized. (a) Thorough disinfection: boil utensils, towels, clothes, and masks for 10-15 minutes; sun books and bedding for 4-6 hours or UV-disinfect for 2 hours; use cresol disinfectant. (b) Ventilate rooms every 10 minutes; 4-5 air exchanges remove 99% of airborne bacilli. (c) Practice separate meals, personal toiletries, frequent handwashing and clothing changes. 2. Periodic lung health examinations detect early cases; do this every 1-2 years. 3. BCG vaccination: It is a live attenuated vaccine derived from M. bovis after serial culture on bile-containing medium. A tuberculin test is usually given first; in low-incidence areas, vaccination may proceed directly. Mantoux conversion at 6-8 weeks indicates immunity; persistent negativity indicates revaccination is needed.

Department to Visit

It is recommended to visit the Infectious Diseases department; an appointment can be booked on this platform before the visit.

Warm reminder: The above information is for health science reference only and cannot replace professional medical diagnosis. If you have related symptoms, please seek medical attention at a regular hospital promptly.