Drug Resistant TB: Emergence of Resistant Strains

Intro

Considering that the TB treatment is so arduous, people often interrupt it. Exact data is hard to to get by, but at least 4% of all TB patients worldwide are resistant to at least one of the current first-line drugs. In parts of Eastern Europe, nearly half of all TB cases resist at least one first line drug.

MDR-TB, defined as resistant to at least Rifampicin and Isoniazid, the two most powerful drugs, might be spreading as fast as 250,000 to 400,000 new cases each year. The treatment relies on "second-line" TB drugs that have far lower efficacy and require even longer administration period, with much higher cost and much higher rate of adverse events.

Diagnosing MDR-TB is also extremely difficult. Most resource-poor settings do not have access to the necessary sophisticated diagnostic equipment. But even in the best of settings that do possess the equipment, it can take up to eight weeks to obtain a result. For patients who are co-infected with HIV; who are already ill, such delays can mean the difference between life and death. In places where lots of HIV/ AIDS cases are present, the risks of MDR-TB spreading like wild-fire is terrifying, but all too likely prospects. To further compound the problem we now have extremely drug resistant TB (XDR-TB). The 2006 XDR epidemic in South Africa sparked international concern about the extent of the crisis and the urgency of finding solutions. Now, concrete action needs to be taken. The WHO needs to take the lead to develop new strategies against the disease . MDR-TB and now XDR-TB are the tips of the iceberg of failing strategies to curb TB.

XDR-TB, which cannot be cured by either by first or second line drugs, is now in 35 countries including all G-8 countries. The case fatality rate exceeds 90% for XDR-TB. The worst hit countries are China, India, Russia and South Africa. The existence of XDR-TB is a serious and emerging public health threat needs to be tackled on a war footing. Population based surveillance data are needed to describe the magnitude of the problem and trends of XDR-TB worldwide. Activities to detect drug-resistant TB accurately and rapidly and treat it effectively should be expanded, including development of international standards for second-line drugs, susceptibility testing, new anti -TB drug regimens and better diagnostic tools. Such measures are crucial if future generations have to be protected from XDR-TB

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Introduction

Tuberculosis (TB) is among the most serious infectious causes of global morbidity and mortality. At present, epidemiologists estimate that one-third of the world population is infected with tubercle bacilli, which is responsible for 8 to 9 million new cases of TB and 2 million deaths annually throughout the world. Approximately 95% of new cases and 98% of deaths occur in developing nations, generally due to the few resources available to ensure proper treatment and where Human Immunodeficiency Virus ( HIV) infections are common.

Although standard anti-tuberculosis regimens have been established for decades, low success rates continue to hamper TB control, resulting in an increased prevalence of Multidrug-Resistance (MDR), mostly due to incorrect regimens and poor patient adherence. Drug-resistant TB may threaten global TB control efforts by reducing the effectiveness of standard short-course chemotherapy and by disproportionately absorbing TB control program resources. Moreover, the emergence of Multidrug-Resistant Tuberculosis (MDR-TB) and more recently, Extensively Drug-resistant Tuberculosis (XDR-TB), presents a formidable challenge to TB control in several settings.

Mycobacterium tuberculosis thus remains a worldwide health care challenge despite the availability of effective antituberculous medications and combination drug therapy.

Drug-resistant

Tuberculosis-Overview

The phenomenon of drug resistance was detected very soon after the introduction of Streptomycin for the treatment of tuberculosis in 1947. Today, with the greatly expanded efforts to strengthen tuberculosis prevention and control programmes worldwide, there is growing concern about the currently reported and potential future rates of drug-resistant tuberculosis, and more importantly, the emergence of multi-drug resistant TB.

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Definition

Drug Resistant Tuberculosis is defined as a case of tuberculosis excreting bacilli resistant to one or more anti-tubercular drugs.  Drug resistance develops either due to infection with a resistant strain, or as a result of inadequate treatment, such as when a patient is exposed to a single drug, or because of selective drug intake, use of inappropriate non-standardized treatment regimens, irregular drug supply, poor drug quality, or rarely, erratic absorption of the medications.

Multi-drug Resistant Tuberculosis is defined as disease due to M.tuberculosis that is resistant to Isoniazid (H) and Rifampicin (R) with or without resistance to other drugs. A strain of MDR-TB originally develops when a case of drug-susceptible tuberculosis is improperly or incompletely treated. This occurs when a physician does not prescribe proper treatment regimens or when a patient is unable to adhere to therapy. Improper treatment allows individual TB bacilli that have natural resistance to a drug to multiply. Eventually the majority of bacilli in the body become resistant.

Multi-Drug Resistant Tuberculosis is a growing hazard to human health worldwide and a threat to tuberculosis control. Management of MDR-TB is difficult, more expensive, challenging and quite often leads to treatment failure.

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