Scientists are battling two highly dangerous forms of the disease that threaten millions.

Last summer’s news that Andrew Speaker, an American with drug-resistant tuberculosis, had taken two transatlantic flights sent travelers into a panic. Like the common cold, TB spreads through the air, so when someone infected with the disease coughs, sneezes, or even speaks, TB germs, or bacilli, are propelled into the atmosphere. In theory, passengers on Speaker’s flights had only to inhale a small number of bacilli to be infected.

Health officials initially feared Speaker had an especially virulent strain of TB known as extensively drug-resistant TB, or XDR-TB, but they later confirmed he had multidrug-resistant TB, or MDR-TB. Both strains are highly dangerous, says Zhenhua Yang, professor of epidemiology at the School of Public Health, who has been studying TB for more than a decade. “These are the two major challenges that are complicating TB control worldwide.”

A third of the world’s population today is infected with Myobacterium tuberculosis, the bacterium that causes most cases of TB. Of those, only five to ten percent will develop the active disease. But the incidence of both XDR-TB and MDR-TB is on the rise, particularly among patients with HIV. In some parts of the world, as many as 70 percent of TB patients have MDR-TB.

In an effort to develop better strategies and methods for TB prevention and control, Yang and a multidisciplinary team of researchers, including colleagues at SPH and the University of Arkansas for Medical Sciences, are combining comparative genomics with epidemiological data analysis and mathematical modeling to try to understand the microbial, host, and environmental factors that affect ongoing TB transmission and the clinical presentation of M. tuberculosis infection.

The group is also working with colleagues at the University of Copenhagen to determine the genetic mechanism that allows M. tuberculosis to survive in a host for decades, despite host immune defense. Noting that TB can develop as long as three decades after infection, Yang says it’s critical that health officials understand how latent infections work if they are to control future transmission of the disease. “If we can identify the primary model for TB survival,” she says, “then we can develop diagnoses and new treatments for latent TB infections.” Latent TB, she adds, “is the major knowledge gap we need to fill.”

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factCHECK, 2007

  • Left untreated, a person with active TB will infect on average between 10 and 15 people every year.
  • Health officials estimate that 1.6 million deaths resulted from TB in 2005.
  • TB is a leading cause of death among people who are HIV-positive.
  • Rates of multidrug-resistant TB (MDR-TB) are especially high in Russia.