German doctor Robert Koch made medical history on 24 March 1882 when he announced that he had isolated the bacilli that caused tuberculosis (TB). But today, 126 years later, TB continues to be the world’s single largest infectious killer. What’s more, the face of TB has changed—it’s no longer a disease equated with poor hygiene and nutrition. Instead, new risk factors are making more and more people, both in developed and developing countries, susceptible to this killer disease. For instance, new studies have highlighted that in India the biggest consequence of smoking is not cancer, but the risk of contracting TB.
Studies also reveal that anything that compromises the immune system of the body puts one at increased risk of TB. Even as the incidence of pulmonary TB remains high, the number of non-pulmonary TB cases—for instance, of the skeletal system and of the stomach—has shown an alarming increase. For the medical and scientific community, one of the biggest challenges is to deal with the increasing number of drug-resistant TB cases. A new World Health Organization (WHO) report estimates that there are about 500,000 new cases of multidrug resistant TB annually, or about 5% of the nine million total new TB cases each year. India and China together account for 40% of all TB cases in the world.
‘Mint’ spoke to T. S. Balganesh, vice-president and head of research, AstraZeneca R&D, which has invested in a multi-million-dollar dedicated research facility in Bangalore to develop a new TB drug.
TB still remains a global challenge. What are the reasons for our failure to eradicate it?
WHO estimates that one-third of the world’s population—that’s about two billion people—is exposed to TB, carry the bug or microbe. The immune system keeps the bug under control. But when the immune system is disturbed, the bug gets reactive. Reactive TB is much more common in patients with conditions such as HIV/AIDS. In fact, HIV/AIDS, which came in the late 1980s, destroyed TB programmes all over the world. In addition, there are factors such as drug-resistant strains of TB—which are more common in Russia and the Baltic states.
Apart from HIV/AIDS, what are the other factors that could weaken the immune system and make you susceptible to TB?
One of the fears which we have in India is the large number of diabetic patients. Improper sugar levels can compromise the immune system. Organ transplant patients who are on immunosuppressive drugs are potentially at risk. Immunomodulatory drugs that are sometimes used in treatment of arthritis can disturb the immune system.
Everything that leads to a compromised immune system can lead to a TB reactivation. So, even the toxic air you breathe—in fact, studies have shown how workers in asbestos factories or miners who inhale dust particles are all at increased risk.
How long does it take for TB to get reactive after exposure?
It could be as low as a month from exposure to disease. And it can be as extended as a lifetime. However, in people with HIV/ AIDS exposed to TB, there are 10% chances of the disease flaring up within a year. But diagnosis in such cases is also more difficult and treatment, too, takes longer time.
What is the biggest challenge in the development of a TB drug?
• The new TB drug has to be compatible with other existing drugs.
• Reducing the duration of treatment is a key challenge—(currently, treatment takes at least six months to a year, leading to poor compliance).
• It has to work on drug-resistant forms of TB.
• The new drug has to be compatible with HIV/ AIDS and diabetes drugs.
• Safety is one of the biggest issues—the new drug should not have any side effects (hepatotoxicity—or liver toxicity—to anti-TB drugs is often a complication).
So, how close are you to developing the new drug?
Well, we hope to have a candidate drug by 2010 and, optimistically speaking, it should take us another two or three years before we can bring it to the market.