Tuberculosis

I. INTRODUCTION

Tuberculosis (TB), chronic or acute infectious disease caused by the bacillus Mycobacterium tuberculosis, which may affect any tissue of the body but is usually found in the lungs. The name ?tuberculosis? is derived from the formation by the body of characteristic cellular structures called tubercles, in which the bacilli are trapped and walled off. The disease rarely occurs in animals in their natural habitat but is often found in domesticated cattle, swine, and fowl.

II. CAUSE OF TB

Tubercle bacilli are transmitted through sputum, mainly in airborne droplets, or by dust particles of dried sputum. They are rarely spread by excreta or food products. Unlike other infectious diseases, tuberculosis has no specific incubation period. A single attack does not confer lasting immunity; rather, the bacilli may remain latent in the body for a long period, until a weakening of the body's resistance affords them the opportunity to multiply and produce symptoms of the disease. Although one third of the world?s population harbours tubercle bacilli, disease symptoms appear in only a relatively small percentage of people. It is most prevalent in areas of overcrowding and poverty. In some countries in Asia, Africa, South America, and Eastern Europe, the prevalence of tuberculosis is several hundred cases per 100,000 population.

III. DETECTION AND DIAGNOSIS

The standard chest X-ray provides a method of mass screening of people for evidence of early pulmonary tuberculosis. Although an X-ray will reveal the presence of a lung lesion, confirmation of its nature requires further testing. The tuberculin test consists of scratching the skin with a protein substance derived from cultures of tubercle bacilli. A positive skin reaction indicates the presence of tuberculosis, whether active or inactive. Diagnosis of active disease is made by the detection of tubercle bacilli in the sputum.
Early stages of infection often produce no symptoms. Symptoms common to all forms of tuberculosis in advanced stages include fever, fatigue, night sweats, loss of appetite, and loss of weight. In pulmonary tuberculosis these symptoms are accompanied by respiratory disturbances such as coughing, chest pains, and production of blood-stained sputum.

IV. HISTORICAL BACKGROUND

In the early 19th century, the work of the French doctors Gaspard Laurent Bayle and Ren? La?nnec established the forms and stages of tuberculosis as a disease entity; both Bayle and La?nnec died of the disease. In 1874 the American doctor Edward Livingston Trudeau, who was also afflicted with tuberculosis, established the Trudeau Laboratory in Saranac Lake, New York. It became a model sanatorium, the kind that for many years was the mainstay of tuberculosis treatment. The German microbiologist Robert Koch discovered the causative organism, the tubercle bacillus, in 1882; in 1890 he developed the tuberculin test for diagnosis of the disease. In 1924 a vaccine, called the BCG (Bacillus Calmette-Gu?rin) vaccine, for individuals exposed to tuberculosis, was developed by the French bacteriologists Albert L?on Calmette and Camille Gu?rin.
The first specific drug for tuberculosis became available when, in 1944, the American microbiologist Selman Abraham Waksman discovered streptomycin. This discovery was followed by the development in 1948 of PAS (para-aminosalicylic acid), and later by isoniazid and other antibiotics that revolutionized the treatment of tuberculosis.

V. TREATMENT

Hospitalization is often required during early stages of treatment, but once the disease has been brought under control the patient may return to normal activity; complete treatment usually takes from six months to two years. Antibiotics such as rifampicin, rifabutin, isoniazid, and pyrazinamide are usually effective against TB when given in varying combinations. Capreomycin is a powerful drug used where resistance to others is evident.

VI. RE-EMERGENCE OF TB

While TB has long been a major problem in developing countries it was widely thought to have been eliminated in the developed world as a result of improved social conditions, mass screening, and the effective use of antibiotics and the BCG vaccine. However, in the 1980s it re-emerged in the West, for example in New York, where several thousand cases were reported. Rising poverty and homelessness, increased migration, overcrowding, drug abuse, and inadequate, or reduced, public health services are all contributing factors. In developed countries many research facilities have been closed, and screening programmes for disadvantaged groups, such as the homeless, are no longer readily available as was the case in previous decades. A major problem is the emergence of new, drug- and antibiotic-resistant strains of TB as a result of patients not completing courses of treatment because they feel better. Increasing numbers of people with AIDS (Acquired Immune Deficiency Syndrome) are developing symptoms of TB because of their lower resistance to disease.
More people are infected with the disease today than at any other time in history. The World Health Organization (WHO) has estimated that 8 to 10 million people catch the disease every year, with 3 million dying from it. It causes more deaths worldwide than AIDS and malaria combined, and it is the world's biggest killer of women. TB "blackspots" include Eastern Europe, with 250,000 cases a year, South East Asia, with 3 million cases a year, and sub-Saharan Africa, with 2 million cases a year. The WHO predicts that by 2020 nearly 1 billion people will be newly infected with TB, and of them 70 million will die.

Reviewed By: John Newell