Why don't we stop tuberculosis?

Thought to be a disease of the past, tuberculosis has surged back with a vengeance, and now kills more people than any other infectious or communicable disease in the world--despite the fact that it is curable.

Tuberculosis, a disease many people associate with sequestered sanatoriums that were long ago abandoned or razed, has now reemerged as the number one killer among the world's infectious or communicable diseases. In 1993 alone, tuberculosis, also known as TB, killed 2.7 million people and infected another 8.1 million. In 1993, an estimated one-third of the world's population, or 1.7 billion people, were infected but had not yet developed the disease.

The current TB epidemic is expected to grow worse, especially in the developing world, because of the evolution of multi-drug-resistant strains and the emergence of AIDS, which compromises human immune systems and makes them more susceptible to infectious diseases. Since the medical knowledge exists to treat and cure TB, "this tragedy is totally unnecessary," Dr. Hiroshi Nakajima, Director-General of the World Health Organization (WHO) said in January.

The resurgence of tuberculosis comes at a time when other infectious diseases that were once thought to be well-controlled--malaria, cholera, and dengue fever among them--have increased and new diseases, notably AIDS, have emerged. Despite the advances in modern medicine, infectious diseases have persisted and continue to have a major effect on public health: in the 50 years following the discovery of antibiotics, efforts to control age-old epidemics have been overcome not by a lack of medical knowledge but by structural problems, including the lack of adequate health care in many parts of the world and increased rates of travel and migration.

Dengue fever, which causes hemorrhaging of the mucous membrane in the skin and abdomen, as well as aches, rash, vomiting, and fever, has been called "the epidemic waiting to happen." Dengue is endemic in Southeast Asia, Africa, and the Caribbean, while malaria is rampaging in sub-Saharan Africa, cholera is breaking out in South America, and the AIDS epidemic is sweeping through Africa, Asia, and the developing world. But the comeback of tuberculosis threatens more people than AIDS, cholera, dengue fever, cholera, and other infectious diseases combined. An estimated 2 to 3 million people were infected with HIV in 1993 worldwide, compared to WHO's estimate of 8 million people infected with TB.

By the year 2000, the global incidence of TB alone is expected to increase to 10.2 million cases per year--an increase of 36 percent over 1990's 7.5 million cases. Three-quarters of this increase can be traced to poor TB control programs, population growth, and the advancing age of the population; the remaining quarter is attributed to the interaction between the TB virus and the HIV virus. AIDS destroys the human cells that keep the TB virus dormant and accelerates the speed at which TB progresses from harmless infection to life-threatening disease. Overall, tuberculosis deaths are predicted to increase by one-sixth, to 3.5 million by the year 2000, killing 30 million people in this decade alone.

"The factors contributing to the increase in tuberculosis are multiple: it is not only HIV, it is not only the emergence of multi-drug resistant strains, and it is not only because of the undermining and weakening of public health services worldwide," says Dr. Jonathan Mann of Harvard University's School of Public Health. "It is all of these things combined." The world is suffering from such a severe epidemic of tuberculosis that the World Health Organization declared a global state of emergency in April 1993.

To complicate matters, the United States and other countries are combatting drug-resistant TB strains. The U.S. National Academy of Sciences' Institute of Health reported in 1992 that M. tuberculosis strains that are virtually resistant to all effective drugs have emerged in cities in the United States and elsewhere, with mortality rates over 50 percent. The academy concluded that a successful control program requires "an arsenal of vaccines and drugs" alongside diagnosis and surveillance.

Tuberculosis has special characteristics that set it apart from other infectious diseases, most of which rely on mosquitos, rats, or water to transmit infection. Tubercle bacilli only live in human tissues, and tuberculosis can only be transmitted by close contact with an infected person. In a healthy individual, the immune system is normally able to wall off and isolate the bacilli in a nodule. This essentially neutralizes the tubercle bacillus, so the person has what is referred to as an inert infection. If the immune system remains strong, there is only a 5 to 10 percent chance of developing TB from an inert infection. But if the immune system is under severe stress--from HIV, diabetes, or chemotherapy for cancer, for example--the chances that the infection will develop into disease increase to as much as 10 percent in a single year.

A person who has active TB can spread the infection simply by coughing, sneezing, singing, or even talking. Another person has only to inhale the bacilli to become infected. If the infection is not detected and treated promptly, one person with active tuberculosis can infect an average of 10 to 14 people in one year and sometimes many more.

The estimated 1.7 billion people who have inert TB infections may show no symptoms at all. Only if those infections are activated will these people be at risk of developing the disease and transmitting it to others. Unfortunately, little is known about what activates a latent TB infection beyond the fact that people with healthy immune systems run a low risk of developing an active case of TB.

Because the already poor and disenfranchised populations of the world carry a disproportionate burden of tuberculosis, the disease has a certain stigma attached to it. But the unsanitary and crowded living conditions that are often connected to poverty do not cause TB to spread; they increase the chances that the infection will spread from person to person and the chances that a person's immune system may already be weak and therefore less able to fight the infection. Despite the misconceptions, tuberculosis is exacerbated only by the failure to detect and treat the infection properly and by close contact with infected individuals.

More than 95 percent of TB cases reported in 1990 were in the developing world, an estimated two-thirds of them in Asia. India accounted for 2.1 million cases. Developing countries are faced with a disproportionate number of cases because AIDS is spreading quickly, health services are inadequate, and little money is available for treatment. But tuberculosis is not limited to the developing world: Eastern Europe, France, Spain, and the former Soviet Union have also reported increases. In the United States, the U.S. Centers for Disease Control and Prevention reported 26,000 cases in 1992, up nearly 20 percent from 1985.

EMERGENT AND RE-EMERGENT DISEASES:
WHAT'S GOING ON?

The New Ones...                    When They Were Noticed

Lyme Disease                               1975
Legionnaires' desease                      1975
Campylobacteriosis                         1977
Toxic shock syndrome                       1978
HIV/AIDS                                   1980
E. coli 0157:H7                            1982
Hantavirus infection           First recognized in U.S. in 1993

The Old Ones...                     Why They Came Back

Tuberculosis                 Erosion of disease control programs,
                                appearance of HIV/AIDS, and
                             increasing volume of immigrations.

Salmonellosis               Increased incidence and antimicrobial
                              resistance associated with animal
                                     husbandry practices.

Pneumococcus                 Increasing antimicrobial resistance.

Listeriosis                          Transport of food.

Dengue                        Spread and ineffective control of
                               mosquitos in tropical regions.

Measles                     Inadequate immunization programs.

Cholera                   Inadequate water supplies and sanitation.

Malaria                      Increasing antimalarial resistance.

Source: Health & Environment Digest, 1993 vol. 7, no. 7. The version printed
here is edited slightly.

Global monitoring by the World Health Organization and regional health NGOs to identify and diagnose TB must be combined with sufficient infrastructure and resources, such as vaccines, medicines, trained health personnel, and clinics. As with other diseases, funding for research and prevention and treatment programs is essential.

Thanks to modern medicine, there is a low-cost, effective TB treatment with high cure rates among infected adults. It relies on four inexpensive drugs (rifampicin, isoniazid, pyrazinamide, and ethambutol) that have a 90 percent success rate if used every day for six to eight months. But if patients don't take the drugs consistently or don't complete treatment, TB strains develop that are more resistant to medicine, and sometimes even untreatable. If this drug regimen were used throughout the world, it would reduce the rate of transmission and cut the number of deaths by half over the next 10 years, according to WHO. In 1993, the World Bank identified short-term tuberculosis treatment as one of the most cost-effective ways to reduce the global burden of disease. In China, it costs only $13 for a supply of all the drugs needed to cure one person. In most developing countries, it costs less than $30 to save a life and prevent further transmission of the disease. In the United States, it costs up to $10,000 to treat an active case of TB compared to $200,000 to treat an active TB infection that has become drug-resistant. Worldwide, early treatment could prevent nearly 12 million deaths in the next decade, and save vast amounts of money.

The growing TB epidemic is a classic case of a public health crisis that could be headed off easily and inexpensively. Its fate will largely depend on the willingness of government and public health officials to invest up front in prevention and early intervention. If we ignore the extraordinary opportunity that exists now to fight the epidemic, we will pay a high price in lives and extensive health care costs later.

Anne E. Platt is a staff researcher at the Worldwatch Institute, where she studies environmental health and fisheries issues.