It's sobering to realize that the ancient scourge, tuberculosis, which has been found in 2,000-year-old mummies, remains a global health threat despite modern medicine. In fact, TB is the leading infectious disease killer in the world, causing nearly 3 million deaths in 1996.



Millions of people -- fully one-third of the world's population -- are infected with the TB bacterium. Five to 10 percent of those will develop the active disease, for reasons we only partially understand. The bacteria can lie dormant for many years, and become active when the host is weakened by factors such as stress, poor nutrition, diabetes, or HIV infection. Once active, TB destroys tissue in the lungs and becomes contagious. Because it is airborne, there is little that can be done to protect against infection.



Antibiotics and public health measures failed to wipe out TB, although until the mid-1980s its rates had been brought very low in the developed world. Then the TB bacteria acquired immunity to many drugs, spreading rapidly among homeless people, AIDS patients, and other vulnerable groups in the United States and abroad.



Several drugs can cure TB, but only if they are taken for many months. With abbreviated treatment, bacteria that have evolved ways of evading the drugs can escape eradication and proliferate as a resistant strain. Then, even when treated with the strongest drugs for two years, the resistant TB is fatal about 60 percent of the time.



Russian prisons are a major source of multi-drug-resistant TB. As tens of thousands of infected inmates re-enter the civilian world every year, TB spreads when they cough and sneeze.



Some experts fear that with the speed and frequency of modern travel, the resistant epidemic could spread to Europe and the United States. To counter the threat of a worldwide epidemic, Western public health officials, like Drs. Golfarb and Kreiswirth of the Public Health Research Institute, are aiding the effort to control resistant TB in Russian prisons.



They are supplying the costly second-line drugs and helping prison health workers ensure that infected inmates take their entire course of drugs -- even if it means the prisoners have to remain in confinement for up to two years past the start of treatment.