The ups and downs of tuberculosis

Tuberculosis is no longer a leading cause of death in the U.S. thanks to the discovery of effective drugs. But recent history reminds us that we must stay vigilant to keep this health threat under control.

Tuberculosis, once called consumption and today often referred to as TB, is a disease caused by the bacterium Mycobacterium (M.) tuberculosis. Although infection usually strikes the lungs (a condition known as pulmonary tuberculosis), the disease can affect other parts of the body: the heart, brain, spine or other bones, intestines, abdomen, kidneys, adrenal glands, or lymph nodes.

M. tuberculosis is a hardy bacterium. It has a tough, waxy cell wall that protects it against a person’s defense mechanisms.

During the 1600s and 1700s, the incidence of tuberculosis increased significantly in both Europe and North America.

Then it declined, possibly due to

• better nutrition and overall improved living and working conditions
• public health advances
• the recognition that tuberculosis is an infectious disease and that patients should be quarantined.

The BCG vaccine makes the scene

Tuberculosis remained the third most common cause of death in the U.S. until the 1900s—topped only by cardiovascular disease and the flu or pneumonia. In 1904, the National Association for the Study and Prevention of Tuberculosis was formed. This organization evolved into the American Lung Association.

Four years later, in 1908, two scientists, Calmette and Guérin, developed a vaccine against tuberculosis. The vaccine was at first called Bacille Bilié Calmette Guérin. (Bacille refers to bacteria and bilié refers to bile, because a growth in ox bile played a role in the vaccine’s development.) This name was soon shortened to BCG. Millions of people have been immunized with BCG. It provides approximately 50% protection against tuberculosis and is especially effective in infants.

A rocky start for antibiotics

In 1944, a team of scientists discovered the antibiotic streptomycin. It could kill 22 different bacteria—including M. tuberculosis. However, it didn’t take long for M. tuberculosis to build up a resistance to streptomycin, and the antibiotic did have some toxic side effects. Another antibiotic, para-aminosalicylic acid (PAS), took the place of streptomycin in the treatment of tuberculosis, but bacterial resistance again developed. Then, the British Medical Research Council discovered that PAS and streptomycin could be used effectively in combination.

Amazingly in 1951 two separate pharmaceutical research groups—one in Germany and the other in the U.S.—simultaneously announced their development of the same agent: isoniazid, a safe and effective antibiotic.

Doctors soon found out that a combination of streptomycin, PAS, and isoniazid could cure most people with pulmonary tuberculosis. While streptomycin could be stopped after several months, a person took the two other antibiotics for 18 to 24 months. That “triple therapy” was the standard of treatment for the next 15 years—allowing hospitals for the treatment of tuberculosis to shut their doors.

Short-course chemotherapy for tuberculosis arrived in the mid-1960s, when rifampin was discovered, and an older drug, pyrazinamide, was reintroduced. Today, the disease can be cured more than 95% of the time as long as people take their medications as prescribed.

Troubling resurgence

All remained quiet on the tuberculosis front in the U.S. until 1986 when, for the first time in more than 3 decades, the number of newly reported cases of tuberculosis started to climb. The trend continued through 1992.

Four factors appear to have driven this turn of events:

• more people immigrating from countries with high tuberculosis rates
• the spread of the human immunodeficiency virus (HIV) infection, which makes people more susceptible to other infections
• the presence of environments in which tuberculosis was more easily spread to others, such as prisons, hospitals, and shelters
• a decline in efforts to control tuberculosis, based on the misconception in the early 1970s that the disease was no longer a health threat.

Then, with the realization of more cases of TB, control efforts were stepped up and the numbers of infected people again began to decline. But, multidrug-resistant strains of tuberculosis bacteria have emerged worldwide.

From American Journal of Respiratory and Critical Care Medicine