Tuberculosis Flashcards
(45 cards)
What causes tuberculosis infection?
Tuberculosis infection is caused by a bacterium called tubercle bacilli.
What is the name of the bacterium responsible for tuberculosis?
The bacterium responsible for tuberculosis is called Mycobacterium tuberculosis.
Besides Mycobacterium tuberculosis, what other bacteria can cause tuberculosis-like infections?
Non-tuberculous (atypical) mycobacteria can also cause tuberculosis-like infections.
How is tuberculosis transmitted?
Tuberculosis is primarily spread through the inhalation of droplets released by coughing individuals with pulmonary tuberculosis.
What happens when the tuberculosis bacillus is inhaled into the lung?
Macrophages ingest the bacillus, and the bacilli replicate within the endosome.
How can tuberculosis spread to other parts of the body?
Tuberculosis can spread through various routes, including the bloodstream (haematogenous), lymphatics to hilar lymph nodes and other lymph nodes, and direct extension to adjacent structures (e.g., pericardium).
What percentage of tuberculosis cases primarily affect the lungs?
Approximately 80% of tuberculosis cases affect the lungs.
Who is at risk of tuberculosis?
Various risk factors include deprivation (homelessness, malnutrition, overcrowding, vitamin D deficiency), alcohol abuse, prisons, immunocompromise (diabetes mellitus, HIV, steroid use), the elderly, and contact with high-risk groups (certain jobs, travel to areas of high incidence).
What are the clinical presentations of pulmonary tuberculosis?
Clinical presentations of pulmonary tuberculosis include a productive cough (not improving with standard antibiotics), haemoptysis, chest pain, fever, night sweats, fatigue, and weight loss.
What are some manifestations of the initial hypersensitivity response to tuberculosis infection?
The initial hypersensitivity response to tuberculosis infection can present with erythema nodosum (painful red nodules on the shins) and phlyctenular conjunctivitis (inflammation of the conjunctiva).
How does the body respond to tuberculosis infection, and what are the different ways the disease may progress?
The body responds to tuberculosis infection by forming granulomas, which are collections of immune cells. The disease can progress in various ways, such as latent tuberculosis infection (asymptomatic), active pulmonary tuberculosis, miliary tuberculosis (spread throughout the body), extrapulmonary tuberculosis (affecting other organs), or tuberculosis reactivation (when latent infection becomes active).
What is the pathogenesis of tuberculosis?
The pathogenesis of tuberculosis involves the inhalation of Mycobacterium tuberculosis (MTB) bacilli into the lungs. The bacilli are taken up by macrophages, which form granulomas. Within the granulomas, the bacteria can remain dormant or cause active disease, leading to tissue damage and the potential for dissemination.
What are the characteristics of pulmonary MTB?
Pulmonary MTB accounts for the majority of tuberculosis cases (55%). It is associated with a higher risk of infection transmission. Cavitatory disease, characterized by the formation of cavities within lung tissue, is more infectious. In the lungs, there is a Ghon focus, which is a granuloma with central caseation and fibrosis. Over time, the Ghon focus may calcify and contain few dormant bacteria.
Describe the characteristics of MTB bacillus.
The MTB bacillus is an aerobic bacterium that requires oxygen to survive. It has a slow growth rate, dividing every 16-20 hours. It has a cell wall but lacks a phospholipid outer membrane. It stains weakly positive with Gram stain but retains stains after treatment with acids, leading to its classification as an acid-fast bacillus.
What diagnostic methods are used for pulmonary MTB?
Diagnosis of pulmonary MTB can be achieved through various methods, including chest X-ray (which often shows upper lobe involvement), sputum culture (three early morning samples), bronchoalveolar lavage (if sputum is not available), Mantoux (Tuberculin test), and Interferon gamma release assay (IGRA)/T-spot test. These tests rely on the host’s cellular immune response to MTB infection.
What are the microbiological diagnostic methods for MTB?
Microbiological diagnosis of MTB includes sputum or bronchoalveolar lavage (BAL) samples, Ziehl-Neelsen (ZN) stain for microscopy, TB cultures (which take 6-8 weeks to confirm diagnosis and determine drug sensitivities), and nucleic acid amplification tests to identify the MTB complex and distinguish it from non-tuberculous infections. PCR can also be used to detect Mycobacterial DNA in various specimens such as pleural fluid, CSF, urine, etc.
What are the stains used for MTB?
The stains commonly used for MTB include the Ziehl-Neelsen (ZN) stain, which shows bright red bacilli against a blue background, and the auramine-rhodamine stain, which utilizes fluorescence microscopy.
What does the histology of MTB show?
The histology of MTB typically reveals granulomatous inflammation with a rim of lymphocytes and fibroblasts. Central infected macrophages, also known as giant cells, are present. Central necrosis, known as caseation, is observed. There is also secretion of cytokines, such as IFNγ, which activate macrophages to kill the bacteria. Acid-fast bacilli (AFBs) may be visualized within the granulomas.
What is the Mantoux/Tuberculin test?
The Mantoux test, also known as the tuberculin test, is a cutaneous immune response test. It involves the intradermal injection of purified protein derivative (PPD) from Mycobacterium tuberculosis. The size of the reaction, measured after 48-72 hours, is graded based on the size of induration. It requires the ability of circulating memory T-lymphocytes to mount a delayed hypersensitivity reaction.
What are the limitations of the Mantoux test?
The Mantoux test may yield false-positive results in individuals who have received the Bacillus Calmette-Guérin (BCG) vaccine and false-negative results in severely ill or immunosuppressed individuals. It can also cross-react with other Mycobacterial antigens, leading to non-specific results.
What is the IGRA/T-spot test?
The IGRA (interferon gamma release assay) or T-spot test is an in-vitro test that measures T-cell activation by Mycobacterium tuberculosis antigens. Blood samples for the test must be analyzed within a few hours. It is more specific than the Mantoux test and correlates better with the degree of exposure to TB. However, it cannot differentiate between latent infection and active disease.
What are the diagnostic methods for tuberculosis?
The diagnosis of tuberculosis involves considering the patient’s history of contact with smear-positive TB, presence of signs and symptoms suggestive of TB, abnormal chest X-ray findings, positive tuberculin test or positive T-spot test, culture of Mycobacterium tuberculosis, and always considering an HIV test.
What is primary TB?
Primary TB refers to the active form of tuberculosis that occurs soon after the initial infection. It accounts for approximately 1-5% of cases, where the bacilli overcome the immune system shortly after infection.
What is latent TB?
Latent TB infection is the majority of cases where individuals have been infected with Mycobacterium tuberculosis but do not have active disease. It represents immune memory of exposure to TB. Approximately 2-23% of individuals with latent TB infection may progress to reactivation disease.
