Tuberculosis is a deadly contagious disease that primarily affects the lungs; it can also attack the central nervous system, circulatory system, genitourinary system, bones, joints and lymphatic system. The abbreviation for tuberculosis is TB for Tubercle Bacillus. A Tubercle is a nodule and Bacillus is a genus bacteria that are rod-shaped, Gram-positive members of the division Firmicutes. TB is common and deadly; caused by the bacterium Mycobacterium tuberculosis.
Of the world’s population, one third is infected with the TB bacterium. Not all infected individuals have the disease, they are carriers. New infections in the world are occurring at one per second. Asymptomatic latent TB will progress to tuberculosis in ten percent of infected patients. Untreated tuberculosis has a mortality rate of over fifty percent. The increase of infected individuals is due to the growth of HIV infections and AIDS.
Patients with an active TB infection are affected in the lungs 75% of the time. When TB affects the lungs it is known as pulmonary TB. Symptoms for pulmonary TB are a chronic, long cough that produces blood or phlegm. The cough lasts for more than three weeks and includes chest pain. Individuals with pulmonary TB also have fever, night sweats, chills, weight loss, appetite loss, fatigue and pallor.
A TB infection that spreads to other parts of the body is referred to as extrapulmonary TB. Sites affected are the pleura (thin, transparent lining on the outside of the lungs and lines the chest wall), the central nervous system as meningitis, lymphatic system (in scrofula of the neck), bone and joints (referred to as Pott’s disease of the spine) and the genitourinary tract, which is referred to as urogenital tuberculosis. A more sever fore is called disseminated or miliary tuberculosis, which produce very small nodules or lesions. Extrapulmonary forms exist mainly in patients with AIDS and young children. Extrapulmonary TB is not contagious.
This disease is difficult to diagnose because to culturing the organism is difficult. A complete physical exam, including medical history and a chest X-ray are required. A procedure known as Tuberculosis radiology is used to diagnose the disease. A tuberculin skin test involves a small prick of the skin with purified protein derivatives of M. tuberculosis. The body will yield a hypersensitive response as a raised, red irritation at the site of the prick. This test is not 100% accurate because it will respond with a positive result in people who are inoculated against TB.
Active pulmonary TB can be viewed as cavities, infiltrates or consolidations (nodules) in the upper lungs. Lesions can appear anywhere in the lungs. When the tuberculosis is disseminated or miliary, a TB pattern of tiny nodules throughout the lungs will be visible. A patient infected with HIV or immuno-suppressed may have TB with a normal chest X-ray or another lung abnormality.
A chest X-ray does not guarantee a complete diagnosis of TB. The bacterium M. tuberculosis produces antigens called early secretory antigen target 6 and culture filtrate protein 10. These are antigens are only present when a person has tuberculosis. There are two blood tests which can detect the antigens: T-SPOT.TB and QuantiFERON-TB Gold. In this test, lymphocytes (white blood cells) are cultured with antigens. If the patient has been exposed to tuberculosis the T lymphocytes will produce interferon γ. The test QuantiFERON-TB Gold will determine the amount of interferon γ when the whole blood is tested with the antigens.
Sputum can also be tested in a suspected case of pulmonary TB.
Cause and Course:
The bacterium, M. tuberculosis, which causes TB, is slow growing. The disease is transmitted through microscopic droplets that are expelled by infected individuals either through coughing, sneezing, speaking and spitting. Uninfected individuals have a 22% chance of being infected if they have enduring, often, or intense exposure to a person with an active pulmonary TB infection. An untreated active pulmonary TB patient can infect up to fifteen people per year. Transmission can only be prevented or stopped through treatment and quarantine of a patient.
Patients infected with M. tuberculosis are mainly asymptomatic (90%) and have only a 10% chance of developing infection tuberculosis. Untreated tuberculosis, however has a mortality rate of over 50%. A TB infection occurs when the bacteria gets into the pulmonary alveoli. The main sight of infection in the lungs is referred to as the Ghon focus. Spread of the disease occurs through the bloodstream. Secondary lesions can grow on lymph nodes, the brain, the bones and the kidneys.
The bacteria are surrounded by granulomas, but are not eliminated by them. The granulomas lead to cell death called necrosis. When TB spreads to the bloodstream and throughout the body it appears as small white tubercles in tissues. This form of TB is called miliary tuberculosis and occurs in the elderly, infants and individuals with suppressed immune systems. The fatality of miliary TB is 20% even with the advanced treatments available.
For many patients the infection grows and hides. Tissue is destroyed and healed, but fibrosis remains. Tissue that is infected is replaced with scarring and the cavities are filled with white necrotic substances. During the active phase the cavities can be linked to the air passages and patients cough up the necrotic material. The material contains live bacterium and this leads to transmissions.
TB is treated with antibiotics, most commonly rifampicin and isoniazid. These antibiotic treatments must last six to twelve months in order to eliminate the bacteria entirely from the body. Latent TB requires usually a single medication. Active TB requires a cocktail of antibiotics due to drug resistance.
Prevention involves two plans. The first is to identify patients with infective TB and the people they are in contact with and quarantine and treat them. The second approach is to vaccinate children. There is no reliable vaccination for adults.
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