New Weapons Against TB

Jan. 18, 2013

By Medical Discovery News

Tuberculosis (TB), the world’s No. 2 killer from a single infectious agent, has a knack for resisting antibiotics. Doctors discovered combining antibiotics had better results, until recent years when TB evolved beyond existing antibiotic cocktails. That may change with a new drug combination that seems to work. 

The new therapy couldn’t come at a better time. Even though TB had been well controlled, it began to make a dramatic comeback in the 1980s. TB, caused by a bacterium called Mycobacterium tuberculosis, infects one person in the world every second. It’s among the top three killers of women and left 10 million children orphaned in 2009.

TB is also the leading cause of death for people with HIV because their weaker immune systems make them vulnerable to the disease. The rise of global HIV infections is largely to blame for the reemergence of TB. Currently, an estimated 14 million people worldwide are co-infected with HIV and TB, and most of them will die without treatment.

TB’s resurgence is also due to drug resistance. To treat people with active, extensively drug resistant strains of TB, doctors prescribe a combination of four drugs: isoniazid, rifampin, pyrazinamide, and ethambutol. Yet in recent years completely drug resistant strains of TB have developed and pose a global threat.

TB is transmitted by inhaling the droplets of an infected person’s sneeze or cough, but also through ingestion. Most infections start in the lungs and initially have no symptoms or at worst feel like the flu. The immune system can wall off the bacteria in what is called a granuloma, a round structure with a core that encases the bacteria and infected cells. Nine out of 10 infections stop at this stage, but some people live with a latent infection for years.

In about 5 percent of cases, the latent TB bacteria reactivate after one to two years. The bacteria replicate rapidly and spread throughout the body. Signs and symptoms of active TB include long-lasting cough bringing up sputum and blood, unexplained weight loss, fatigue, fever, night sweats, chills, loss of appetite, pain with breathing or coughing, and chest pain. Though TB most often affects the lungs, it can also involve the genitourinary system, bones, joints, lymph nodes, and peritoneum.

If TB bacteria’s proliferation is not controlled by the immune system, a severe form of the disease called miliary TB develops. The bacteria eventually cause extensive and progressive damage to the structure of the lungs and ultimately death.

With the new drug combination, fewer people will suffer these ravaging consequences. One new cocktail is called PA-824 and consists of moxifloxacin, a relatively new antibiotic, and pyrazinamide, an older TB drug. The combination works faster than current therapies, and doesn’t seem to interact with HIV drugs.

At least three other drugs or combinations are in the testing phase, just in time to treat multiple-drug-resistant forms of this deadly disease. If effective, the drugs will help a global initiative to reverse the spread of TB by 2015.

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