tuberculosis

tuberculosis (TB), contagious, wasting disease caused by any of several mycobacteria. The most common form of the disease is tuberculosis of the lungs (pulmonary consumption, or phthisis), but the intestines, bones and joints, the skin, and the genitourinary, lymphatic, and nervous systems may also be affected.

There are three major types of tubercle bacilli that affect humans. The human type ( Mycobacterium tuberculosis ), first identified in 1882 by Robert Koch , is spread by people themselves. It is the most common one. The bovine type ( M. bovis ) is spread by infected cattle but is no longer a threat in areas where pasteurization of milk and the health of cattle are strictly supervised. The avian type ( M. avis ) is carried by infected birds but can occur in humans. The tubercle bacillus can live for a considerable period of time in air or dust. The most common means of acquiring the disease is by inhalation of respiratory droplets.

Course of the Disease

Tuberculosis of the lungs usually results in no or minimal symptoms in its early stages. In most persons the primary infection is contained by the body's immune system, and the lesion, called a tubercle, becomes calcified. In many the infection is permanently arrested. In others the disease may break out again and become active years later, usually when the body's immune defenses are low. Untreated, the infection can progress until large areas of the lung and other organs are destroyed. Symptoms of the disease include cough, sputum, bleeding from the lungs, fever, night sweats, loss of weight, and weakness.

Incidence

The incidence of tuberculosis of the lungs, the "white plague" that formerly affected millions of people, declined from the 1950s until 1984; sanatoriums were closed and routine screening was abandoned in the United States. Then, between 1984 and 1992, the incidence increased by 20%, chiefly because of immigration from countries where it is common and because of AIDS , which leaves people particularly vulnerable to the disease. Renewed efforts at control and advances in treatment have been rewarded with incidence declines each year, amounting to a total decline of 31% from 1992 to 1998.

Worldwide the outlook has been far less encouraging. In 1993 the World Health Organization declared TB a global health emergency. Approximately one third of the world's population is infected, and an estimated 1.6 million die each year. The vast majority of new cases occur in sub-Saharan Africa. Spread of TB is especially rapid in areas with poor public health services and crowded living conditions. In homeless shelters and prisons, crowded conditions and inadequate treatment often go together. Areas where living conditions are disrupted by wars, famine, and natural disasters also are heavily affected.

Especially alarming has been the spread of drug-resistant strains of TB. By the late 1990s scientific experts and international health officials warned that drug-resistant strains were spreading faster than had been anticipated. Bacteria can survive and become drug resistant in patients whose treatment is not properly monitored and seen to completion. Multidrug resistant (MDR) TB strains are resistant to two or more of the commonly prescribed first-line drugs, while extensively drug resistant (XDR) strains are also resistant to three or classes of the more toxic second-line drugs. Some believe that unless major new treatment strategies are initiated in source countries, drug-resistant TB will eventually become epidemic even in areas with good control programs, such as Europe and America.

Diagnosis and Treatment

Diagnosis is made by a tuberculin skin test. It can be confirmed by X rays of the chest and sputum examination. Ideally, treatment begins after a skin test signals exposure but before active disease has developed. The treatment of choice for prevention and for active cases is the antimicrobial drug isoniazid (INH), available since 1956. In infected individuals it is usually used in combination with other antituberculosis drugs such as rifampin, pyrazinamide, and ethambutol. Tuberculosis drugs have to be taken regularly, typically for 6 to 12 months. Many patients abandon their treatment when they feel better; similarly, preventive treatment is often abandoned because of the inconvenience. Such noncompliance is believed to be the main reason for the upsurge in drug-resistant strains of the TB bacilli, many of which are resistant to more than one drug. Drug-resistant TB is difficult to treat and has a much higher death rate; extensively drug resistant TB is especially worrisome because it can be essentially untreatable.

The combination drug rifater (rifampin, isoniazid, and pyrazinamide) has simplified drug administration. Directly observed treatment, where health-care workers watch patients take each dose of medicine, has proved effective in eliminating the problem of noncompliance in the United States, but monitoring has been less effective in many other parts of the world.

Prevention of Tuberculosis

Preventive measures include strict standards for ventilation, air filtration, and isolation methods in hospitals, medical and dental offices, nursing homes, and prisons. If someone is believed to have been in contact with another person who has TB, preventive antibiotic treatment may have to be given. Infected persons need to be identified as soon as possible so that they can be isolated from others and treated.

An antituberculosis vaccine, bacille Calmette-Guérin, or BCG vaccine, was developed in France in 1908. Although there is conflicting evidence as to its efficacy (it appears to be effective in 50% of those vaccinated), it is given to over 80% of the world's children, mostly in countries where TB is common; it is not generally given in the United States. Federal health officials in the United States have stated (1999) that a new vaccine is essential to TB prevention. It is hoped that the determination of the complete DNA (genome) sequence of Mycobacterium tuberculosis, achieved in 1998, will hasten the development of an effective vaccine.

Bibliography

See R. Dubos, The White Plague (1955); S. A. Waksman, The Conquest of Tuberculosis (1964).

tuberculosis (TB) Infectious disease caused by the bacillus Mycobacterium tuberculosis. It most often affects the lungs (pulmonary tuberculosis), but may involve the bones and joints, skin, lymph nodes, intestines, and kidneys. One-third of the world's population is infected, and up to 5% of those infected eventually develop TB. Poor urban living conditions have lead to a resurgence of the disease in the USA and much of Europe, where previously it had been in decline. The BCG vaccine against tuberculosis developed in the 1920s and the first effective treatment drug, streptomycin, became available in 1944. However, the bacillus shows increasing resistance to drugs and some strains are multi-resistant.

tuberculosis has been known in Ireland since early times, but it became a major scourge, especially in urban areas, in the late 19th and early 20th centuries. In 1906 tuberculosis caused nearly 16 per cent of all Irish deaths. Two sanatoriums were built in the 1890s, but attempts to make tuberculosis a notifiable disease were opposed by Irish politicians and tuberculosis remained a major killer throughout the 1920s and 1930s. The Women's National Health Association, established in 1907 by Lady Aberdeen, took the lead in attempts to combat the disease. However, it was only in the late 1940s that tuberculosis became a notifiable disease in Ireland, both north and south. At the same time a Tuberculosis Authority was established in Northern Ireland, which helped reduce the number of cases substantially during the 1950s, and Dr Noel Browne, the Irish health minister, launched a campaign that within a matter of a few years had brought tuberculosis under control in the Republic as well.

Elizabeth Malcolm