Mycobacterium tuberculosis (MTB) is the bacterium that causes tuberculosis (TB), a serious infectious disease. This microscopic organism primarily targets the lungs, though it can affect other body parts. TB is a significant global public health concern, posing challenges for healthcare systems worldwide.
Understanding Tuberculosis
Tuberculosis primarily affects the lungs (pulmonary TB), but the bacteria can also spread to other body parts, such as the kidneys, spine, or brain, causing extrapulmonary TB. Symptoms vary depending on the affected organ.
A distinction exists between latent TB infection (LTBI) and active TB disease. In LTBI, Mycobacterium tuberculosis is inactive in the body, causing no symptoms and not spreading to others. Active TB disease means the bacteria are multiplying, causing illness, noticeable symptoms, and potential transmission. Common symptoms of active pulmonary TB often include a persistent cough lasting three weeks or longer, accompanied by fever, night sweats, and unexplained weight loss. Individuals may also experience chest pain or coughing up blood.
How Tuberculosis Spreads
Tuberculosis spreads through the air when a person with active pulmonary TB coughs, sneezes, or speaks, releasing airborne droplets containing the bacteria. People nearby can then inhale these droplets, leading to infection. Transmission does not occur through casual contact, such as shaking hands, sharing eating utensils or food, or touching surfaces.
Exposure to an individual with active TB disease is a primary risk factor for developing the infection. A weakened immune system significantly increases the likelihood of progressing from latent infection to active disease. Conditions like HIV infection, diabetes, or certain medications that suppress the immune response contribute to this vulnerability. Living in crowded or unsanitary conditions also raises the risk of exposure and subsequent infection.
Diagnosing Tuberculosis
Diagnosing Mycobacterium tuberculosis infection involves medical tests to detect the bacteria or the body’s immune response. For latent TB infection, two primary tests are utilized: the tuberculin skin test (TST) and interferon-gamma release assays (IGRAs). The TST involves injecting tuberculin protein under the skin; a positive reaction is a raised, firm bump after 48-72 hours, reflecting an immune response. IGRAs, performed using a blood sample, measure interferon-gamma release in response to TB-specific antigens, indicating prior exposure.
For diagnosing active TB disease, a chest X-ray is often performed to identify abnormalities in the lungs, such as infiltrates or cavities. Sputum smear microscopy examines lung mucus under a microscope, using an acid-fast bacilli (AFB) stain to visualize the bacteria. TB culture remains the definitive method for confirming active disease, growing bacteria from a patient’s sample in a laboratory, which also enables drug susceptibility testing. Molecular tests, such as PCR-based assays, offer rapid detection of Mycobacterium tuberculosis genetic material and can also identify genetic markers associated with drug resistance, providing quicker insights for treatment planning.
Treating Tuberculosis
Tuberculosis is a curable disease, though successful treatment necessitates a prolonged course of antibiotic medications. For individuals diagnosed with latent TB infection, preventive treatment regimens are prescribed to avert progression to active disease. These regimens are typically shorter, often lasting three to four months, and involve one or two specific antibiotics, aiming to eliminate the inactive bacteria before they can cause illness.
Active TB disease requires a more extensive and multi-drug treatment approach. The standard initial regimen commonly involves four different antibiotics, such as isoniazid, rifampin, ethambutol, and pyrazinamide, taken daily. This intensive phase typically lasts for two months, followed by a continuation phase with fewer drugs, extending the total treatment duration to six to nine months. Completing the entire prescribed course of medication is of paramount importance, even if symptoms improve or disappear.
Stopping treatment prematurely significantly increases the risk of TB recurrence and, more concerningly, the development of drug-resistant strains. Drug-resistant TB, including multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB), presents a substantial challenge. MDR-TB is resistant to at least isoniazid and rifampin, the two most potent first-line drugs. XDR-TB is even more complex, exhibiting resistance to additional second-line medications, making it much harder to treat and requiring longer treatment durations, often 18 to 24 months, with less effective and more toxic drugs.
Preventing Tuberculosis
Preventing the spread and impact of tuberculosis involves a combination of individual and public health strategies. The Bacillus Calmette-Guérin (BCG) vaccine is employed primarily in countries with high TB burdens. This vaccine is administered to infants and young children to protect against severe forms of TB, such as TB meningitis and disseminated TB. However, its effectiveness in preventing pulmonary TB in adults is variable and generally limited.
Early diagnosis and prompt, effective treatment of individuals with active TB disease represent a cornerstone of prevention. By identifying and treating active cases quickly, the chain of transmission is broken, preventing further spread of the bacteria within communities.
Public health initiatives also play a significant role in control efforts. These include contact tracing, which involves identifying and screening people who have been in close contact with an individual with active TB. Screening high-risk populations, such as those with weakened immune systems or individuals living in congregate settings, helps identify infections early. Improving living conditions, including reducing overcrowding and enhancing ventilation, also contributes to preventing transmission. Global control programs, such as the World Health Organization’s (WHO) End TB Strategy, aim to reduce TB incidence and mortality through expanded access to diagnosis and treatment, research into new tools, and addressing social determinants of the disease.