Why can\'t we be free of disease?

by Jonathan Briggs

Why can't we be free of disease? Despite the best efforts of scientists, bacterial and viral infections continue to plague people all over the world.

Tuberculosis (TB) has infected humankind for at least 7,000 years; malaria for perhaps half that time. AIDS, on the other hand, has reached epidemic proportions within only the past 25 years. With the first advent of vaccines and antibiotics, physicians and health officials had hopes of controlling and even wiping out infectious disease, but, so far, only one smallpox has been officially declared "eradicated."

The Chinese first used vaccination to combat smallpox in the16th century. But it took more than another century for the technology to be used in the West, when the British physician Edward Jenner successfully inoculated a child against "the pox" in 1796. And although it took nearly another 200 years, smallpox was the first communicable disease to be eliminated worldwide. The last reported case was in Somalia in 1977, and the World Health Organization (WHO) declared the disease eradicated in 1980. Only two living samples of the virus that causes the disease still exist, locked away in laboratories.

WHO set the year 2000 as the target date to also eradicate polio, using global immunization with a vaccine. But what about malaria, yellow fever, and AIDS? Why can't they be eradicated as well? The problem lies in the fact that there's more to eradicating a disease than just designing and distributing a vaccine two steps that are seldom simple, easy, or quick. Producing a safe and effective vaccine and then distributing and administering it requires extensive research and enormous resources, not to mention worldwide cooperation.

What do we really mean by eradication? In the case of smallpox, eradication means that the virus has been removed from both people and the environment. What the WHO calls "eradication" of polio refers only to elimination of the virus from people; some scientists believe there will still be live poliovirus in the environment. Eradication of all traces of a disease like smallpox requires the presence and coordination of many factors, including:

• Worldwide interest in the project
• A disease with a relatively long incubation period
• A disease that is easy to detect and is not highly contagious
• A disease in which humans are the only reservoir for the causative virus and there is no intermediary carrier
• A resilient vaccine that is easy to provide to less developed nations

Few of the other well known infectious diseases, including polio, share this profile. Many are either difficult to diagnose, have short incubation periods, are transmitted easily from human to human, or are carried by insects or animals. Some have all these characteristics. And for many there are no vaccines.

Then, too, there are the new scourges. Human immunodeficiency virus (HIV), which came on the scene only about 25 years ago, continues to wreak havoc, particularly in Africa. Although more limited geographically, the Sin Nombre Hanta virus of the American southwest appeared only about 10 years ago.

And if that's not enough bad news, the incidence of several of the familiar infectious diseases we thought we had under control, including malaria and diphtheria, is on the rise.

In addition, some strains of the bacteria that cause syphilis, gonorrhea, pneumonia, meningitis and many other infections are developing resistance to antibiotics. The Institute of Medicine (IOM), a unit of the National Academy of Sciences, predicts that despite our best scientific efforts, many of these communicable diseases will persist, and even increase, in the near future.

Funding makes a difference, too. TB is a case in point. According to an IOM report released in May 2000, control of TB in the United States has been marked by a pattern of neglect that should not be repeated. When medical advances led to a decline in the number of cases, Congress responded in 1972 by eliminating all funding dedicated to fighting the disease. As a result, TB public health systems collapsed, infection rates jumped during the late 1980s, and deadly drug-resistant strains emerged. It took high-cost control measures to deal with the outbreak, and the disease is now at an all-time low in this country about 68 active cases per million with the rate dropping by about 7% each year.

The reasons that we've not yet been able to completely eradicate infectious diseases are many and varied, but nearly all have to do with human activities, such as:

• Increases in population density and urbanization
• Increases in the numbers of people whose immune systems are suppressed or compromised
• Changes in agricultural practices and conditions
• The presence of humans in previously unpopulated areas
• Global warming
• Worldwide travel and trade
• Changes in the microbes that cause, and the insects and animals that carry, these diseases
• Deterioration of public health systems because of wars and complacency

Obviously, the problem is wide in scope. And agencies such as the IOM, the WHO, and the Centers for Disease Control and Prevention (CDC) are responding by increasing surveillance of these diseases so that outbreaks and their sources are identified and controlled more quickly. To complicate things further, airplane travel makes it possible for a person infected in one hemisphere to carry a disease to the other side of the world in a matter of hours, or for a person with no natural immunity to a regional disease to encounter it unprepared. Fortunately, surveillance, rapid response, and continually improving medical care are sufficiently able to keep these diseases contained or controlled.