A wise man should consider that health is the greatest of human blessings, and learn how by his own thought to derive benefit from his illness.
—HIPPOCRATES
THE EARLIEST HUMAN or hominid ancestors are four to five million years old. Modern humans date back at least several hundred thousand years. A tick or two on the evolutionary clock, but a respectable span of time nonetheless. During those years humans have endured infectious disease. They have suffered through the great pestilences—smallpox, bubonic plague, tuberculosis, cholera, typhus, malaria, influenza, yellow fever, and others. At the dawn of human evolution we can only guess at the nature of the diseases that afflicted our ancestors.
One great “civilizing” event that produced many new and deadly infections for humanity about ten thousand years ago was the introduction of agriculture. Nomadic hunter-gatherers settled down with their domesticated animals—cattle, pigs, horses, sheep, goats, chickens—and received a healthy dose of their microbes. To quote Arno Karlen in Man and Microbes, “Agriculture brought humans so many new pathogens that it seems wondrous they survived.” The most prevalent infectious disease, the common cold, made the cross-species leap from horses to humans four to five thousand years ago. Hundreds of other diseases have made a similar jump from animals to humans.
As populations steadily increased and big cities developed, communities became large enough to permanently sustain certain disease germs. Circulating among the people, these pathogens would always find new susceptibles to infect. Society had entered the age of crowd diseases and epidemics.
The human species has survived. Will it continue to do so in the face of emerging and extremely virulent pathogens? In all likelihood, yes. Logic dictates that if we have survived to this point, largely without the benefit of antibiotics, immunization, public sanitation, or an understanding of the germ theory or the nature of disease transmission, we will survive whatever future pestilence nature fashions to infect us with. Still, circumstances exist today that have not existed in the past, greatly increasing the survival threat.
First of all, there are more people in the world today than there have ever been—6.2 billion compared to 2.5 billion a mere fifty years ago. The figure increases daily. More people means a greater population density—overcrowding. Very often there is inadequate living space or food to support the number of people living in a given area. The economy of the region cannot provide adequate health care or sanitation. This is a recipe for disaster. Infectious diseases are spread most rapidly among individuals living in close quarters, with poor sanitation, whose systems have become immunocompromised by poor nutrition and who are unable to receive proper health care. These conditions are obviously most pronounced in developing nations, where vaccine-preventable diseases such as measles, mumps, and polio and controllable diseases such as cholera, malaria, and worm infections still kill millions of people each year.
Developed nations, however, are not exempt. In the United States it is surprising how poorly standard public health services are conducted. Some of the statistics are astonishing. In 1993 an adviser to the World Health Organization announced that the United States had fallen behind Albania, Mexico, and China in childhood vaccination. The United States ranks twenty-ninth in the world on infant mortality and an incredible forty-ninth in the world on child immunization for nonwhite children. Laurie Garrett sums it up in The Coming Plague: “We kill our children.”
Fifty million people drink unfiltered water in America. Not surprisingly, waterborne microbes—such as rotavirus, the world’s leading cause of diarrhea—continue to infect, sicken, and kill. Each year thousands of people die in the United States from infections by the familiar food-borne bacteria salmonella and shigella. The reason: improperly inspected and handled eggs, poultry, and beef.
Tuberculosis and AIDS remain serious threats in the United States, Canada, and Europe—and they are uniting in a frightening scenario that makes each much more deadly in combination than alone.
Jet travel has brought the human population—all six-plus billion of us—together. We live increasingly in a world community where no one is more than a half day away from anyone else. The doors of most nations are open to globe-trotters. It is a phenomenon that did not exist before the mid-twentieth century.
It creates a melting pot for pathogens and for disease transmission. The extremely virulent viruses emerging from the rain forests—Ebola, Marburg, Lassa—are not isolated to those areas. Air travel has brought Lassa and Ebola across the Atlantic from Africa to the United States. AIDS evolved in Africa in monkey primates and is now a global problem. The geographical barriers—oceans, mountains, and sheer distance—that once isolated an outbreak of disease, providing “regional quarantine,” no longer do. To quote one epidemiologist, “We are all in it together.”
And then there is bioterrorism. The battle to defeat the pathogens is difficult enough; add to that the human incentive to destroy other humans through disease infection, and the task becomes daunting, especially in light of the “global togetherness” that air travel has brought about, and the ease of manufacture and dissemination of lethal germs in today’s highspeed, high-tech world.
To this point we have been lucky on all fronts. Mass infection through bioterrorism has not occurred. The most common yet potentially dangerous bacterial infections—strep and staph—remain susceptible to at least one antibiotic, vancomycin. The most virulent or most lethal infections—Ebola, Marburg, AIDS—are not easily transmitted. But what if common pathogens become resistant to all antibiotics? Enterococci that cause many ear infections are already demonstrating this capability, and they can easily pass their vancomycin-resistant genes to other, deadlier bacteria. What if AIDS or Ebola becomes airborne and as easily spread as the flu or the common cold? Given the conditions that exist today, it is a chilling thought.
The latter part of the twentieth century brought, along with extensive air travel, an unprecedented tampering with the environment. Governments are learning the hard way that dam building, deforestation, and the like all create new opportunities for microbes and their natural hosts to interact with humans. In the case of Lyme disease it was not the deforestation, but reforestation of treeless tracts of land in New England that brought us into intimate contact with the deer tick. Pretty, wooded suburban areas were created that attracted people as well as deer and rodents. The Lyme bacterium was not newly evolved—sporadic cases of Lyme disease had appeared for decades—but the disease became epidemic when changed environments afforded the bacterium new opportunity to infect.
In short, any sort of ecological change engenders a risk of disease to humans. Legionnaires’ disease was another “new” ailment that struck as an epidemic in 1976, killing 34 of 221 people who fell ill. But the Centers for Disease Control and Prevention (CDC) investigation of frozen blood samples from unusual or unexplained pneumonias revealed that Legionella pneumophila had been around causing occasional and isolated cases of disease since 1947 or earlier. It was, however, the introduction of artificial environments in the form of cooling towers and hot tubs that bred and released Legionella into the air. It is now common throughout the world and is a significant cause of hospital pneumonia.
“To write about infectious disease is almost to write about something that has passed into history.” These words were expressed by Nobel Prize-winning virologist Sir Macfarlane Burnet in 1962 (A Dancing Matrix, Robin Marantz Henig). Clearly he was mistaken. Forty-odd years later the message is evident: we must maintain a constant vigil. It has been estimated that improved public sanitation has extended the average life expectancy in the United States twenty years, and the advent of antibiotics and other drugs another ten. These efforts must continue and be broadened to the world stage. Programs must be implemented nationwide and worldwide by organizations such as WHO, the NIH, and the CDC to vaccinate people and to provide and properly administer antibiotics and chemotherapies. Improvements must be made in living conditions and public sanitation—especially water and food supplies. Global computer information networks must be set up to provide surveillance of infectious disease outbreaks, patterns of transmission, and mortality. Statistics must be collected and evaluated continually. And we must be more respectful of our environment and tread on it more lightly.
It is a task much easier said than done. The commitment in money and manpower would be enormous and could be accomplished only with worldwide cooperation. Richer nations would have to shoulder the greater load financially. But there is no alternative. To quote from an article in the New York Times (June 10, 1994), “The devastating appearance of AIDS as a worldwide epidemic put this generation on notice that it could face new or rapidly emerging threats from infectious disease. The resurgence of tuberculosis has reminded us that diseases once vanquished can return with a vengeance. These are horrible reminders that the fight against pathogens is never over.”
There is little doubt that the fourth horseman—pestilence—has saddled up and is charging at us with lance poised. Hopefully we can parry his thrusts.