TB:
- Tuberculosis is caused by various strains of mycobacterium, usually Mycobacterium tuberculosis.
- It usually attacks the lungs but can also affect other parts of the body.
- It is spread through the air when people who have active MTB infection cough, sneeze, or spit.
- In most cases the disease is asymptomatic, latent infection, and about 10% latent infections eventually progresses to active disease.
- If untreated, it kills 50% of its victims.
- One third of the world’s population is thought to be infected with M. tuberculosis, and every second a new infection occurs.
- About 80% of the population in many Asian and African countries test positive in tuberculin test.
DRUG RESISTANT TB
- Until 50 years ago, there were no medicines to cure TB.
- Now, strains that are resistant to a single drug have been documented in every country surveyed.
- Drug-resistant TB is caused by inconsistent or partial treatment, when patients do not take all their medicines regularly for the required period because they start to feel better, because doctors and health workers prescribe the wrong treatment regimens, or because the drug supply is unreliable.
- A particularly dangerous form of drug-resistant TB is multidrug-resistant TB (MDR-TB), which is defined as the disease caused by TB bacilli resistant to at least isoniazid and rifampicin, the two most powerful anti-TB drugs.
- Rates of MDR-TB are high in some countries, especially the former Soviet Union, and threaten TB control.
MDR-TB
- TB that is resistant at least to isoniazid and rifampicin the two most powerful first-line anti-TB drugs are called the Multidrug-resistant tuberculosis (MDR-TB).
- It develops because the when the course of antibiotics is interrupted and the levels of drug in the body are insufficient to kill 100% of bacteria.
- This means that even if the patient forgets to take medicine, there are chances of developing MDR-TB.
- MDR-TB is treated with second line of anti-tuberculosis drugs such as a combination of several medicines called SHREZ (Streptomycin+isonicotinyl Hydrazine+Rifampicin+Ethambutol+pyraZinamide) +MXF+cycloserine.
XDR-TB
- When the rate of multidrug resistance in a particular area becomes very high, the control of tuberculosis becomes very difficult.
- This gives rise to a more serious problem of extensively drug-resistant tuberculosis (XDR-TB).
- XDR-TB is caused by strains of the disease resistant to both first- and second-line antibiotics.
- This confirms the urgent need to strengthen TB control.
- Thus, Extensively-drug resistant TB (XDR-TB) is a sub-set of MDR-TB which is further resistant to at least two more drugs which are second line drugs and is thus virtually incurable.
TDR-TB
Totally drug-resistant tuberculosis (TDR-TB)
- It is TB which is believed to be resistant to all the first and second line TB drugs.
- TDR-TB has resulted from further mutations within the bacterial genome to confer resistance, beyond those seen in XDR- and MDR-TB.
- Development of resistance is associated with poor management of cases. Drug resistance testing occurs in only 5% of TB cases worldwide.
- Without testing to determine drug resistance profiles, MDR- or XDR-TB patients may develop resistance to additional drugs.
- TDR-TB is relatively poorly documented, as many countries do not test patient samples against a broad enough range of drugs to diagnose such a comprehensive array of resistance.
- The United Nation’s Special Program for Research and Training in Tropical Diseases has set up a TDR Tuberculosis Specimen Bank to archive specimens of TDR-TB.
