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Chapter 5

Tuberculosis

With S. J. WAMBANI and PAUL REEVE

There was a time in the eighteenth and nineteenth centuries when tuberculosis was a fashionable affliction. All the best poets, musicians, and writers, not to mention politicians and heroines of operas, suffered from consumption and died either beautifully or in interesting ways. Of course, the unknown poor simply died, often unpleasantly, of the white plague. There were many names for this common disease, which has been recognized and described for centuries: the earliest definitive record is of pulmonary and spinal tuberculosis in the mummy of a 5-year-old Egyptian child of about 3400 B.C. A later mummy, of a young man dated at about 1000 B.C., had a psoas abscess as well as spinal lesions. In the Americas, a naturally mummified middle-aged Peruvian woman who died about 1000 years ago had primary pulmonary tuberculosis with calcified hilar lymph nodes. Tuberculosis was identified in this case because a unique DNA segment was identified in a lung lesion, using the polymerase chain reaction.

The word "tubercle" was first used in the seventeenth century by a Dutchman, Franciscus Silvius, of Leyden, to describe the lung lesions. Later (1839), Johann Schönlein called the disease "tuberculosis." It was not until 1882 that Robert Koch identified and described Mycobacterium tuberculosis. With this discovery much of the romance and many of the myths vanished.

If the source had been found, the cure had not, and tuberculosis continued as a major cause of death and no respecter of social rank: it was familiar and fatal to everyone. Probably more than 25% of the graves in the cemeteries of Europe and America were filled by people of all ages who had died of tuberculosis. There is a large and interesting literature on the disease and the remarkable ways in which it was treated. Most were in some way or other uncomfortable for the patient, and none were very successful. Then in 1943, Selman Waksman, a microbiologist at Rutgers University, fortuitously discovered streptomycin while investigating a peculiar fungus which was killing chickens. This discovery, together with the development of two other drugs in the next few years, led to the apparent conquest of tuberculosis.

But the bacillus which had undoubtedly affected history by killing so many in their youth may well have the same power once again. In 1993 the World Health Organization (WHO) declared that tuberculosis was a global emergency and estimated that it would kill 30 million people in the next decade. In 1996 it was the leading cause of deaths due to micro-organisms: there are eight million new cases every year. One-third of the world's population (1.7 billion) have been infected at some time and 20 million currently have active tuberculosis. (On average, about 10% of those infected go on to develop clinically active disease.) More than half of all those who have been infected live in Asia and Africa. WHO estimates (1995) that only 10% of tuberculous patients also have AIDS, but in the next decade there may be seven million with the combined infection, rising to 14 million by the year 2010. Almost every patient with both diseases will have active tuberculosis, because the AIDS virus destroys the cell which normally controls the micobacteria. (See Chapter 8 for discussion of tuberculosis in AIDS.)

The global rise in population, the wars and disputes which have caused refugees and migration, and the decline in the level of public health services are also to blame for the recent reemergence of tuberculosis.

WHO has shown (in Tanzania) that it is possible to find and cure over 80% of infectious cases and that 6-8 months of proper treatment will achieve this goal. The sputum bacterial counts fall rapidly and the sputum becomes negative for bacilli within 2 months of adequate treatment, resulting in control of the epidemic spread. In 1997, WHO was a little more optimistic that tuberculosis might be leveling off but warned that failure to treat the infection promptly would result in drug resistance, which is already at a level of at least 7% and rising and often takes the form of multidrug resistance.

Against this background it is important to add that "tropical" tuberculosis is not a product of the AIDS epidemic. This chapter in the first edition (1981) started by stating that "The causative organism of tuberculosis, Koch's bacillus, is morphologically and culturally the same in the tropics as in non-tropical countries. Yet the clinical disease "tuberculosis" appears in ways which may be unrecognizable to physicians trained in non-tropical countries. It is not a "chronic" disease in the majority of patients, but an acute and often fulminating infection whether it be in the chest, bones, joints or elsewhere. Moreover, it causes signs and symptoms and presents at sites which may be quite unexpected and contrary to the descriptions in many North American and European textbooks." To this it is now necessary to add, "unless those books refer to AIDS-related tuberculosis."

Both in the tropics and in HIV-positive patients, the difference lies in the immunological background, the state of nutrition, and the way of life; it is that mystical relationship between the bacillus and its host which changes the clinical course of the disease, aided by variations in the virulence of particular strains of bacilli. Tuberculosis in the tropics often mimics an infection in an immunosuppressed patient; it must be remembered as the possible etiology of almost any acute or unusual illness whether seen in the tropics or in a recent immigrant into nontropical countries, and this pattern of tuberculosis must not be assumed to be due to AIDS. There are many other common causes of immunosuppression. And in the same way, a person from a nontropical area moving into the tropics retains the nontropical pattern of disease; transplanting one's person does not immediately change one's nature. Only over several years may this phenomenon of "host-response" alter to the local pattern, unless a virus or other event intervenes.

Acute tuberculosis with unusual variations is not the monopoly of the tropics; the authors have seen cases following the severe "tropical" pattern in patients who do not have AIDS and who have spent their lives in North America or in Europe. Tuberculosis is a disease of infinite variation because it occurs in an infinite variety of people. The immunosuppression due to HIV infections has focused worldwide attention on the pattern of tuberculosis which has been the norm in the tropics, as it may well have been in the past wherever nutrition, hygiene, and living conditions were poor and parasites were plentiful.

Dr. Olive Shisana, Director General of the South African Department of Health and joint author of a 1996 WHO report, has summed up the situation: "Tuberculosis has become a disease more terrifying than AIDS or the Ebola virus." Worldwide, it is the principal cause of death amongst all adults. Referring to drug resistance, Dr. Donald Enarson, Director of the International Union Against Tuberculosis, based in Paris, has added, "This is the most frightening situation I have ever encountered. If we do not act now, we will have a situation that we cannot control."

Radiologists in the tropics or, indeed, anywhere else, should consider tuberculosis in almost every differential diagnosis: its manifestations, like its sufferers, are legion.

Synonyms

TB. Koch's disease. Pulmonary tuberculosis: Phthisis. Consumption. Tabes pulmonalis. Spinal tuberculosis: Pott's disease. Abdominal tuberculosis: Tabes mesenterica. Tuberculous cervical lymphadenitis: Scrofula. Struma. General tuberculosis: Hectic fever. Asthenia. Ger: Tuberkulose. Schwindsucht. Sp: Tisis, Tuberculosis. Fr: Phtisie.

Definition

Tuberculosis is an infection with the Mycobacterium tuberculosis or Mycobacterium bovis. Both are gram-positive, acid and alcohol fast, aerobic, non-spore forming rods, classified with the actinomycetes. M. tuberculosis is a facultative intracellular parasite, which, many believe, is capable also of extracellular growth and can remain dormant for years or even decades.

Geographic Distribution

Tuberculosis is a worldwide infection from which some three million people die annually, more than from any other single infectious disease. It is probable that, because of AIDS, drug resistance, and population stresses, the epidemic will increase in the future unless brought under control. The countries with the largest number of patients with tuberculosis are Bangladesh, Brazil, China, India, Indonesia, Nigeria, Pakistan, the Philippines, and Vietnam. The rate of disease is highest in sub-Saharan Africa. In some parts of the world, 80% of the population react positively to a tuberculin skin test by the age of 25 years and many react much earlier (unless they are HIV-positive). In developing countries tuberculosis accounts for 26% of avoidable deaths.

The reported incidence, however, may not be accurate: it is often a reflection of the efficiency and methods used to detect the disease rather than a true indication of its actual prevalence. Public health facilities vary greatly, but, for example, it was estimated in East Africa (1971) that half a million persons were newly infected each year and that 75,000 would develop clinical tuberculosis, of whom only 25,000 would be diagnosed and 16,000 treated. Such figures have improved in some countries, but not in all. A person, once infected, is likely to harbor the tubercle bacillus for the rest of his or her life and it may remain dormant unless there is a change in general health or immunity, as occurs with AIDS, diabetes, leukemia, or malnutrition. Much less commonly, there may be reinfection.

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Copyright: Palmer and Reeder