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Tuberculosis (TB) is the second most common infectious disease to cause death in humans and each year, about two million people die from TB (Varaine, Henkens & Grouzard, 2010 ). Tuberculosis has been affecting the human population from ancient times and still persists, despite the availability of modern antibiotics. Tuberculosis was common in societies of ancient Rome and Greece. Evidence of tuberculosis has been found as far back as Egyptian mummies. Throughout history, it has been called by many names like phthisis, consumption and white plague, all of which refer to the wasting nature of the disease. Before the discovery of antibiotics, TB was generally fatal, but nowadays, with proper treatment, nearly all cases of TB are curable. Despite the availability of treatment, there has been a global resurgence of TB cases since the 1980s and it was declared as a global health emergency by World Health Organization (WHO) in 1993. Socio economic issues like poverty, poor sanitation, overcrowding, malnutrition, HIV and partial treatment have created drug resistant strains of bacteria, which allow TB to persist even after massive efforts to eliminate the disease (NIAID, 2012). This essay describes the causative organism, route of transmission, risk factors, signs and symptoms, diagnosis, treatment and prevention of TB.
Tuberculosis is caused by Mycobacterium tuberculosis, also called tubercle bacilli (TB). M. tuberculosis bacteria belong to the family Mycobacteriaceae and is a slow growing, single-cell, aerobic, non-motile, rod-shaped microorganism found only in humans. It divides every 16 to 20 hours. M. tuberculosis is larger than other bacteria, measuring about 1 to 4 micrometers in length and 0.3 to 0.6 micrometers in width. It has a cell wall made up of complex lipids, which provide an effective barrier against many drugs, which explains why TB is a persistent and stubborn infection. M. tuberculosis is resilient and very adaptable and can quickly become immune to anti-TB drugs, giving rise to resistant strains (Jindal, 2011).
Routes of transmission
Tuberculosis is an airborne disease. M. tuberculosis is carried in droplet nuclei, which are airborne particles with diameters of 1-5 microns. Infectious droplet nuclei are produced when a patient of pulmonary TB coughs, spits, sneezes, shouts or sings. Droplet nuclei can remain suspended in air for a long time and transmission of infection occurs when a healthy person inhales these particles. The bacillus travels through upper respiratory tract and bronchi to reach the alveoli of lungs. From lungs, the bacillus may spread to other organs of the body via blood or lymph (CDC, 2010).
All individuals infected with TB bacteria do not necessarily develop tuberculosis, as the bacillus can exist in latent state in the body. However, known risk factors for developing the disease include poor, unsanitary or overcrowded living conditions, malnutrition, very young or old age, immuno-compromised state such as in HIV or during chemotherapy and prolonged contact with an infected person (CDC, 2010).
Clinical Signs and Symptoms
Tuberculosis may be pulmonary or extra pulmonary. Pulmonary tuberculosis has many specific respiratory and non specific constitutional signs and symptoms, which generally appear only when the disease is in an advanced stage. Constitutional symptoms consist of fever, malaise, weight loss, tiredness, anorexia (loss of appetite), sweating at night and headache. Respiratory symptoms consist of chronic cough (more than 2 to 3 weeks), hemoptysis (blood in the sputum), breathlessness, chest pain and hoarseness of voice (Jindal, 2011).
Extra pulmonary tuberculosis occurs in about 15 to 20 % of all TB cases. The most commonly involved extra pulmonary sites are the lymph nodes, bones, joints, pleura and the central nervous system (CNS). Extra pulmonary TB presents non specific signs and symptoms, depending upon the organ involved. In case of TB of lymph nodes, there may be single or multiple, usually bilateral adenopathies. In skeletal TB, there is arthritis or osteitis accompanied by bone pain and loss of movement. Gastrointestinal TB may cause diarrhea, abdominal pain and anal bleeding. TB in CNS can cause meningitis, headache, stiff neck, vomiting, photophobia and fits. On performing a physical examination, the doctor may find signs like clubbing of fingers or toes, swollen lymph nodes, pleural effusion and unusual breath sounds (crackling) (Jindal, 2011).
Diagnosis and Treatment
Early diagnosis and prompt treatment is of utmost importance, not only for the patient, but also for the community to prevent the spread of infection to others. Diagnostic tools include chest X-ray, chest CT scan, sputum culture, bronchoscopy, thoracentesis, tuberculin skin test and in rare cases, biopsy of the affected tissue (CDC, 2010).
TB is treated with multiple antibiotic drugs taken for six to nine months, depending upon the regimen followed. The most commonly prescribed drugs are Isoniazid, Rifampin, Pyrazinamide and Ethambutol. Other drugs that can be used include Amikacin, Ethionamide, Moxifloxacin, Para-aminosalicylic acid and Streptomycin. It is imperative that the treatment should be completed and all drugs taken for the prescribed length. Failure to do so may lead to a relapse of the disease and the bacteria becoming resistant to antibiotics. Infection by drug resistant bacteria produces drug resistant TB which is harder to treat and has a higher mortality rate (CDC, 2010).
Since TB is an airborne disease, its transmission can be prevented by adequate ventilation and limiting contact with patients. WHO recommends administration of BCG (Bacille Camllette- Guerin) vaccine to infants in those parts of the world where the disease is most prevalent (Dugdale, 2011).
Despite our understanding of the causative and risk factors for development of tuberculosis and the availability of strong antibiotics to fight bacteria, M. tuberculosis continues to evade our efforts at elimination. More research into this disease is the need of the hour as we require newer, more efficacious vaccines, more effective drugs and shorter drug regimens to improve patient compliance. An accurate and quick diagnosis is also critical to successful treatment and checking the transmission of the disease, for which we need better diagnostic tools.