The control of tuberculosis: a continuous game
of snakes and ladders

Introduction

Tuberculosis (TB), which had been controlled to be a significant extent during the nineteen sixties and seventies, has re-emerged in recent years as one of the leading causes of death in the world. Nearly 3 million people die every year due to TB. A world Health Organization report of 1997 states that there are, world-wide, 8.8 million new cases every year meaning about 1,000 new cases every hour. Most of these are resistant to the presently available antitubercular drugs. This works out to 52,000 deaths per week, or 7,000 deaths each day and constitutes a grim reminder of the apparent failure of medical science to counter an ancient scourge. Tuberculosis got its present name at the end of the 19th century. Under its previous name of consumption it has been long known as a world-wide phenomenon. It is caused by a bacterium, Mycobacterium tuberculosis. A related organism, M.bovis, causes TB in cattle while M.Leprae is the causative agent of leprosy in man. The non-pathogenic mycobacterium. M.smegmatis is comparatively safe to work with and is often used in the laboratory as a model to understand the physiology of the members of the entire genus since it grows more rapidly in liquid culture in the laboratory than the pathogenic organisms. (M.tuberculosis takes 15-21 days for optimal growth in stationary liquid culture.)

Through the ages, the contribution of TB to the misery of mankind has been immeasurable. About 70 years ago, as small boys, the authors of this article underwent the traumatic experience of seeing a very close relative (in one case the mother and in the other an aunt) suffering from TB. In those days the only treatment available was a normal diet supplemented with calcium tablets, cod liver oil and an occasional injection of gold suspension. Until the advent of independence in 1947 and the more or less simultaneous beginning in the use of streptomycin, there was no generally available treatment for TB I India. Rest in a sanatorium situated in a salubrious place with an unpolluted atmosphere was strongly recommended but not always possible. When the racking coughs and the accompanying fever become severe, surgical intervention was sometimes attempted. This could take the extreme form of thoracoplasty (removal of ribs) for the closure of cavities, or removal of one of the lungs. Often a merciful death intervened.

In many respects we live in a different world today. While normally reliable drugs for the treatment of TB are at hand, the proliferation resistant strains and the association of TB and AIDS are beginning to pose major problems. The recent deciphering of the complete genomic sequence of M.tuberculosis (Cole et al 1998) has given a major impetus to attempts to tackle the disease by using the techniques of modern molecular biology and immunology. The significance of knowing the DNA sequence of M. tuberculosis can hardly be exaggerated, for it is a matter of urgency to devise new therapeutic and prophylactic measures. At the same time, we need to acknowledge that in the past, major successes in the fight against infectious diseases (including TB) have come, not so much from new drugs as from improvements in nutrition and the adoption of public health measures such as better sanitation, provision of safe drinking water, isolation of symptomatic individuals and so on. Records from many countries testify to this (figure 1). Where do we stand today in India with regard to the fight against TB? The aim of this essay is to provide a personal perspective of TB-related research in post-independent India, an evaluation of the work done so far and a peep into the future. We do so from two points of view, those of basic science (TR) and medicine (PC). Most reference to the literature prior to 1994 will be found in Ratledge and Stanford (1982), Ramakrishnan (1983) or Bloom (1994).

Tuberculosis in India : From tragedy to optimism

TB has been described as far back as 600 BC in the Sushruta Samhita, a compendium of ancient medicine and surgery. In Sanskrit the disease is known as Kshaya, `wasting disease', or Raja Yakshmaa, "the king of diseases". The second name may be related to the fact that among its sufferers was said to be the moon, the king of stars. There were said to be four causes of the disease: overstrain, suppression of natural urges, wasting (for example, due to grief, anxiety or longing) and a promiscuous diet, any of which could cause the three morbid humours Vata, Pitta and Kapha to flare up. The premonitory symptoms ranged from `pallor of the eyes' to finding fault in the service of dinner'; a person with a full-blown case of Raja Yakshmaa could suffer from `fullness of the head', `cough', pain in the sides', and so on. A treatment based on the principles of Ayurveda, the classical Indian system of health and healing, was provided. Besides medicines, dietary prescriptions were detailed; alcohol in moderate quantities, the flesh of birds and animals which inhibit dry areas and goat's milk were among the items recommended. Some sages were of the opinion that the disease could be spread from person to person and listed it in the class of communicable diseases alongwith leprosy, fevers, conjunctivitis and syphilis. All said and done, TB was rare until the second half of the nineteenth century. Concomitant with the growing population density caused by industrialization, its incidence has increased progressively since then (Wilkinson 1914).

One of the earliest sanatoria in the country was established in 1915 in Madanapalle in the state of Andhra Pradesh. Among the persons treated there during the 1940s pre-chemotherapy days was PC's aunt. After visits during the summer months for several years, the physicians at the sanatorium recommended thoracoplasty. She did not survive the operation. The emotional strain caused by this episode eventually led PC to decide on taking up TB as his clinical speciality. Happening to become a staff member of the very same sanatorium in 1955, he reviewed the case history and x-rays of his aunt and was astonished to discover how long she had led an active and cheerful life in spite of gross pathology in the lungs.

Ever since Koch (1932) isolated M. tuberculosis in 1882 and demonstrated that it was the aetiological agent of the disease, efforts were under way to control the growth of the organism. Calmette and Guirin isolated an attenuated culture of M. bovis, a member of the tuberculosis complex, named Bacillus Calmette - Guirin (BCG). BCG was shown, first in animals and then in neonates, to function as a vaccine against TB. BCG is even now administered to infants, but it has been found that protection is confined to about 10 years and is effective only during childhood. In spite of the availability of potent antitubercular first-line drugs like isoniazid, pyrazinamide and rifampicin, and a number of second-line drugs added every year, the incidence of TB in India and worldwide has risen alarmingly in recent years.

By 1900 it had become clear that the Western method of dealing with the problem of TB namely, training of specialists, increasing the number of beds and `running several vehicles', often in different directions was inappropriate to the Indian situation, which was characterized by meager resources. In spite of this realization, a property thought-out national TB control programme (NTP) that combined elements of prevention (BCG vaccination), establishment of clinics, rehabilitation centres and basic research had to await the recommendations of the Bhone committee in 1945. The names of those who provided leadership in the early days of the programme deserve to be remembered; P.V..Benjamin, architect of the NTP; J.Frimodt Mvller, responsible for the first BCG trial in the country; B.K.Sikhand, who vigorously advocated domiciliary treatment and home care; Rajnarayan and S.P.Pamara, both epidemiologists; M D Deshmukh, who favoured a camp approach; and P K Sen, who studied how the infection was transmitted between individuals living or working in close proximity to one another. All of them shared an extraordinarily strong commitment to their goals.

One of the steps taken right at the beginning was the mass BCG campaign launched in 1951. For the first time a strategy was evolved to reach rural areas and it had a good deal of success. The NTP was born in 1962 it was a people-oriented programme, with the concepts of integration and the principles of primary health care built in and involving the health services of the entire country. It went on to be scientifically tested and implemented in two districts of the country, Tumkur in Karnataka and Ananthapur in Andhra Pradesh. The aim of the NTP was to cut the transmission of the infection through proper and adequate treatment. The focus was on identifying those who excreted tubercle bacilli in their sputum. A study showed that the yield from the first two specimens was 80%; additional specimens did not contribute anything substantial. Diagnosis of non-pulmonary TB (which is non-infectious and constitutes 15-20% of all cases) was by a two-referral system. There was no attempt to consider eradication of the disease, since TB unlike, for example, small pox does not qualify for the criteria necessary for eradication. The main problems with regard to TB are that (i) there is a long incubation period, (ii) both subclinical and clinical cases occur; (iii) reinfection and reactivation of latent infections play a prominent role in the development of disease, (iv) the effectiveness of vaccination is still uncertain, BCG being effective only during childhood, and (v) immunity is either partial or doubtful (cell-mediated immunity is unstable; it can be lowered in acute viral infections, during treatment with cytotoxic drugs and steroids, metabolic disorders like diabetes and AIDS). These factors also make it unlikely that an effective biomarker for TB can be discovered in the near future. At any rate, no reliable serodiagnostic test is currently available for extra-pulmonary TB (Chauhan 1997).

As with many progressive measures in this country, in actual implementation NTP did not prove to be a success. This is evidenced by the fact that in the nearly 40 years since its inception the number of TB positives in the country has actually increased (table 1), albeit with phases of decline now and then. The reason for this soon became clear. NTP depended completely on keeping the patient on a four drug regimen continuously till his sputum became free of microorganisms. The advantages of this regimen are two-fold. Firstly, it prevents the emergence of drug - resistant strains of M. tuberculosis. Secondly, since most of the anti-TB drugs are hepatotoxic, a four-drug regimen permits the lowering of the dose of individual drugs to a level at which their hepatotoxicity in lo. In practice this criterion was often never fulfilled. Many private physicians prescribed only one drug at a time and changed over to a new one when the first proved no longer effective. Patient tended to stop taking drugs once they started feeling better. The result was that after an initial period of improvement, many patients started harbouring M. tuberculosis strains that were resistant simultaneously to several drugs and they also infected healthy people. The situation has improved slightly after 1997 when WHO introduced the DOTS (directly observed therapy short course) system in which patients are closely monitored continuously for six months. However, statistics from a study in Baku, Azerbaijan (reported in Lancet 353 369-973, 1999) show that only 71% of those who completed DOTS were cured, many of the patients turning out to have harboured drug-resistant strains before the start of the treatment (a clear distinction between relapse and re-infection in such patients is yet to be established). To sum up, the need to develop new drugs against M. tuberculosis remains an important one; and basic research on the biochemistry and molecular biology of the organism is essential if we are to have any hope of doing so.

Metabolism and chemotherapy : Beginnings
The XIV International Tuberculosis Conference was held for the first time in India in New Delhi in 1957 under the presidentship of P V Benjamin, Advisor to the Government of India and architect of the National TB Programme. One of us (TR) attended the conference and in the same year started work on the metabolism of M. tuberculosis H37Rv and other mycobacteria in the then Pharmacology Laboratory of the Indian Institute of Science, Bangalore. M Siris had set up facilities there for testing on tubercle bacilli, grown both in vitro and in experimental mice and guinea pigs, compounds synthesized in the Department of Organic Chemistry by B H Iyer and his group. The work that was initiated in 1957 had three aims : (i) To study the enzyme systems of virulent bacilli and compare them with those reported in the human host, so that any differences could be exploited for a possible chemotherapeutic attack against TB; (ii) to compare the enzyme systems of the drug-sensitive and drug-resistant strains and to study the mechanism of resistance to drugs such as isoniazid and streptomycin India and (iii) to compare the enzyme systems of virulent and avirulent strains to find out the possible cause of virulence.
Compared to the situation at present, during the early years after independence research in India had to be carried out under somewhat demanding circumstances. Two examples may suffice to drive home the point. It was difficult to obtain even a standard biochemical like adenosine triphosphate (ATP); the worker had to prepare it from rabbit muscle after anaesthetizing the animal by repeated injection of magnesium sulphate solution into the ear vein and isolating its muscle. Another common situation was that it often became necessary to calibrate capillary glass tubes with mercury because micropipettes were not readily available in the country. Apart from overcoming such hurdles, until 1961 the work had not yielded any significant results on market differences between the enzyme systems of the virulent and avirulent strains of mycobacteria, on the one hand, and between virulent mycobacteria and a commonly occurring bacterium like Escherichia coli on the other.
In that year, a fortuitous meeting at Delhi with Jacques Monod convinced TR that only the application of the newly emerging area of molecular biology could clarify the mechanism of virulence and drug resistance of M. tuberculosis H37Rv. At the time the obvious place to learn the techniques connected with this discipline was the USA . TB, however, had cased to be a menace there and there was no prominent laboratory in the USA carrying out research on the disease (a situation that prevailed until the emergence in the 1980's of AIDS and its attendant complications). The necessary techniques had to be learnt while working on E. coli in the universities of Yale, California (Berkeley) and Michigan with the hope of adapting them later to M. tuberculosis.