Medical Discovery NewsBy Drs. David Niesel and Norbert Herzog
Tuberculosis (TB), the world’s No. 2 killer from a single infectious agent, has a knack for becoming resistant to antibiotics. Scientists discovered combining antibiotics gave better results, until in recent years, TB evolved to become resistant to the currently used antibiotic cocktails. That may change with a new drug combination that seems to have promise.
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.
It’s the leading cause of death for people with HIV. The rise of HIV infections and the resulting immunosuppression is one reason for the reemergence of TB. An estimated 14 million people worldwide are co-infected with HIV and TB. Without treatment, most of them will die.
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.
Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professors David Niesel of the University of Texas Medical Branch at Galveston and Norbert Herzog of the Frank H. Netter School of Medicine at Quinnipiac University in Hamden, Conn. Learn more at www.medicaldiscoverynews.com.