Killer Diseases—The War Between Man and Microbe

Revenge of the Microbes

CDC, Atlanta, Ga.

The 20th century has seen marvelous advances in medical science. For thousands of years, humans have been virtually helpless against the scourge of deadly microbes. But things began to change in the mid-1930's when scientists discovered sulfanilamide, the first substance that could defeat bacteria without seriously harming the infected person.*

In the years that followed, scientists developed powerful new drugs to fight infectious diseases-chloroquine to attack malaria and antibiotics to subdue pneumonia, scarlet fever, and tuberculosis. By 1965 more than 25,000 different antibiotic products had been developed. Many scientists concluded that bacterial diseases were no longer of great concern or research interest. After all, why study diseases that would soon no longer exist?

In the world's developed countries, new vaccines dramatically decreased the toll of measles, mumps, and German measles. A mass polio vaccination campaign, launched in 1955, was so successful that cases of the disease in Western Europe and North America plummeted from 76,000 in that year to fewer than 1,000 in 1967. Smallpox, a major killer disease, was eradicated worldwide.

This century has also seen the invention of the electron microscope, a device so powerful that it enables scientists to see viruses that are a million times smaller than a man's fingernail. Such microscopes, along with other technological advances, have made it possible to understand and fight infectious diseases as never before.

Victory Seemed Assured

In the wake of these discoveries, the medical community was full of confidence. The microbes of infectious disease were falling to the weapons of modern medicine. Surely the victory of science over microbe would be swift, decisive, complete! If a cure for a specific disease was not already available, it soon would be.

As early as 1948, U.S. secretary of state George C. Marshall boasted that the conquest of all infectious diseases was imminent. Three years later, the World Health Organization (WHO) asserted that Asian malaria could soon be a disease "no longer of major importance." By the mid-1960's, the belief that the era of plague and pestilence had passed was so widespread that U.S. surgeon general William H. Stewart told health officers it was time to close the book on infectious diseases.

Old Diseases Return

However, the book on infectious diseases was in no way ready to be closed. Microbes did not vanish from the planet just because science had invented drugs and vaccines. Far from being defeated, well-known killer microbes returned with a vengeance! In addition, other deadly microbes surfaced-microbes previously unknown to doctors. Thus, microbes both old and new are on the rampage, threatening, afflicting, or killing countless millions of people worldwide.

	"In hospitals alone, an estimated one million bacterial infections are occurring worldwide every day, and most of these are drug-resistant." World Health Organization

Killer diseases once thought to be under control have surfaced again, more deadly than ever and more difficult to treat with drugs. One example is tuberculosis (TB). WHO stated recently: "Since 1944, TB drugs have been put to extensive use in Japan, North America and Europe to dramatically reduce TB cases and deaths. However, TB control efforts in less developed countries have been neglected, . . . enabling the disease to return to wealthy countries in more dangerous, multidrug-resistant forms." Today TB, usually caused by airborne bacteria that lodge in the lungs, kills about three million people every year-over 7,000 per day. By the year 2005, the death toll could soar to four million each year.

Other old-time killers are also on the rise. Cholera is now endemic in many parts of Africa, Asia, and Latin America; it afflicts and kills increasing numbers of people. An entirely new strain has emerged in Asia.

Dengue, spread by the Aëdes aegypti mosquito, is also rapidly on the rise; it now threatens 2.5 billion people in over 100 countries worldwide. Since the 1950's, a deadly new hemorrhagic form of the disease has emerged and spread throughout the Tropics. It is estimated that it kills about 20,000 people each year. As with most viral diseases, there is no vaccine to protect against the disease and no drug to cure it.

Malaria, which science had once hoped to eradicate, now kills about two million people each year. Both the malaria parasites and the mosquitoes that carry them have become increasingly difficult to kill.

Devastating New Diseases

Perhaps the best known of the new diseases that have recently arisen to plague humankind is deadly AIDS. This incurable disease is caused by a virus unknown only a dozen or so years ago. Yet, by late 1994 the number of people worldwide who were infected with the virus was between 13 and 15 million.

Other previously unrecognized infectious diseases include hantavirus pulmonary syndrome. Transmitted by field mice, it appeared in the southwestern United States and proved fatal in more than half the reported cases. Two types of hemorrhagic fevers-both new, both fatal-have developed in South America. Other dreadful diseases have also arisen-viruses bearing strange, exotic names-Lassa, Rift Valley, Oropouche, Rocio, Q. Guanarito, VEE, monkeypox, Chikungunya, Mokola, Duvenhage, LeDantec, the Kyasanur Forest brain virus, the Semliki Forest agent, Crimean-Congo, O'nyongnyong, Sindbis, Marburg, Ebola.

When Microbes Fight Back A small microbe known as a bacterium "weighs as little as 0.00000000001 gram. A blue whale weighs about 100,000,000 grams. Yet a bacterium can kill a whale."-Bernard Dixon, 1994. Among the most feared bacteria found in hospitals are drug-resistant strains of Staphylococcus aureus. These strains afflict the sick and the weak, causing deadly blood infections, pneumonia, and toxic shock. According to one count, staph kills about 60,000 people in the United States each year-more than those who die in car accidents. Over the years, these strains of bacteria have become so resistant to antibiotics that by 1988 there was only one antibiotic effective against them, the drug vancomycin. Soon, however, reports of vancomycin-resistant strains began to surface from around the world. Yet, even when antibiotics do the job they're supposed to do, other problems may arise. In mid-1993, Joan Ray went to a hospital in the United States for a routine operation. She expected to be home in just a few days. Instead, she had to remain in the hospital for 322 days, primarily because of infections she developed after surgery. Doctors fought the infections with heavy doses of antibiotics, including vancomycin, but the microbes fought back. Joan says: "I couldn't use my hands. I couldn't use my feet. . . . I couldn't even pick up a book to read it." Doctors struggled to find out why Joan was still sick after months of antibiotic treatment. Laboratory work showed that in addition to staph infection, Joan had another kind of bacteria in her system-vancomycin-resistant enterococcus. As the name suggests, this bacteria was unharmed by vancomycin; it also seemed to be immune to every other antibiotic. Then doctors learned something that flabbergasted them. The bacteria not only resisted the drugs that should have killed it but, contrary to what they expected, it actually used vancomycin to survive! Joan's doctor, an infectious-disease specialist, said: "[The bacteria] need that vancomycin in order to multiply, and if they don't have that they won't grow. So, in a sense, they're using the vancomycin as food." When the doctors stopped giving Joan vancomycin, the bacteria died, and Joan got better.

Why Are New Diseases Emerging?

With all the knowledge and assets possessed by modern medical science, why are killer microbes proving so difficult to defeat? One reason is the increased mobility of today's society. Modern transportation can quickly make a local epidemic global. Jet travel makes it easy for a deadly disease to move, harbored inside an infected person, from one part of the world to any other part of the world within hours.

A second reason, which favors the microbe, is the explosive growth of the world's population-especially in cities. Of course, garbage is produced in cities. Garbage contains plastic containers and tires filled with fresh rainwater. In the Tropics, that results in the multiplication of mosquitoes that are carriers of killer diseases such as malaria, yellow fever, and dengue. In addition, just as a thick forest can fuel a fire, so high-density population provides ideal conditions for the rapid spread of tuberculosis, influenza, and other airborne diseases.

A third reason for the return of the microbe has to do with changes in human behavior. Microbes that are transmitted sexually have flourished and spread as a result of the unprecedented scale of multiple partner sex relations, which have characterized the latter part of the 20th century. The spread of AIDS is just one example.^#

A fourth reason why killer microbes are proving so difficult to defeat is that man has invaded the jungles and rain forests. Author Richard Preston states in his book The Hot Zone: "The emergence of AIDS, Ebola, and any number of other rain-forest agents appears to be a natural consequence of the ruin of the tropical biosphere. The emerging viruses are surfacing from ecologically damaged parts of the earth. Many of them come from the tattered edges of tropical rain forest . . . The tropical rain forests are the deep reservoirs of life on the planet, containing most of the world's plant and animal species. The rain forests are also its largest reservoirs of viruses, since all living things carry viruses."

Humans have thus come into closer contact with insects and warm-blooded animals in which viruses harmlessly reside, reproduce, and die. But when a virus "jumps" from animal to human, the virus may become deadly.

The Limitations of Medical Science

Other reasons why infectious diseases are making a comeback relate to medical science itself. Many bacteria now defy antibiotics that once killed them. Ironically, antibiotics themselves have helped to create this situation. For example, if an antibiotic kills only 99 percent of the harmful bacteria in an infected person, the surviving one percent that resisted the antibiotic can now grow and multiply like a superstrain of weeds in a newly plowed field.

Patients aggravate the problem when they do not finish a course of antibiotics prescribed by their doctor. Patients may stop taking tablets as soon as they begin to feel better. While the weakest microbes may have been killed, the strongest survive and quietly multiply. Within a few weeks, the disease reoccurs, but this time it is harder, or impossible, to cure with drugs. When these drug-resistant strains of microbes invade other people, a serious public-health problem results.

Experts at WHO stated recently: "Resistance [to antibiotics and other antimicrobial agents] is epidemic in many countries and multi-drug resistance leaves doctors with virtually no room for manoeuvre in the treatment of an increasing number of diseases. In hospitals alone, an estimated one million bacterial infections are occurring worldwide every day, and most of these are drug-resistant."

	Blood transfusions spread deadly microbes

Blood transfusions, used increasingly since the second world war, have also helped to spread infectious diseases. Despite the efforts of science to keep blood free of deadly microbes, blood transfusions have contributed significantly to the spread of hepatitis, cytomegalovirus, antibiotic-resistant bacteria, malaria, yellow fever, Chagas' disease, AIDS, and many other dreadful diseases.

State of Things Today

While medical science has witnessed an explosion of knowledge during this century, there remain many mysteries. C. J. Peters studies dangerous microbes at the Centers for Disease Control, America's foremost public-health laboratory. In an interview in May 1995, he said concerning Ebola: "We don't know why it's so virulent for man, and we don't know what it's doing [or] where it is, when it's not causing these epidemics. We can't find it. There's no other virus family . . . that we have such a profound ignorance about."

Even when effective medical knowledge, drugs, and vaccines exist to fight disease, applying them to those in need requires money. Millions live in poverty. WHO's World Health Report 1995 states: "Poverty is the main reason why babies are not vaccinated, why clean water and sanitation are not provided, why curative drugs and other treatments are unavailable . . . Every year in the developing world 12.2 million children under 5 years die, most of them from causes which could be prevented for just a few US cents per child. They die largely because of world indifference, but most of all they die because they are poor."

By 1995, infectious diseases and parasites were the world's biggest killers, snuffing out the lives of 16.4 million people each year. Sadly, countless millions of people live in conditions that are ideal for the emergence and spread of deadly microbes. Consider the lamentable situation today. Over a billion people exist in extreme poverty. Half the world's population lack regular access to medical treatment and essential drugs. On the streets of polluted megacities wander millions of abandoned children, many of whom inject drugs and practice prostitution. Millions of refugees languish in unhygienic camps amid cholera, dysentery, and other diseases.

In the war between man and microbe, conditions have increasingly favored the microbe.

* Sulfanilamide is a crystalline compound from which sulfa drugs are made in the laboratory. Sulfa drugs can inhibit bacterial growth, allowing the body's own defense mechanisms to kill the bacteria.

^# Other examples of sexually transmitted diseases: Worldwide there are some 236 million people infected with trichomoniasis and about 162 million people with chlamydial infections. Each year there are approximately 32 million new cases of genital warts, 78 million of gonorrhea, 21 million of genital herpes, 19 million of syphilis, and 9 million of chancroid.