Some years ago, humans won the war against smallpox, following its demise could be any of poliomyelitis or measles. All credit to the vaccines, medical scientists, and efforts by the World Health Organization (WHO) and other bodies that make such achievements possible. But there is a darker side to humankind’s confrontation with communicable disease — they retreat never to surrender. Raging on many fronts, this is a battle that will never be completely won. It is one in which our enemies are ever likely to challenge us in ways to which we simply cannot respond.
The awesome power of microbes such as viruses and bacteria over human affairs is extensively illustrated by the great epidemics of the past. In the 14th century, the Black Death killed one third of the entire population of Europe within about four years. Later, as Napoleon’s armies marched back and forth across the continent, typhus and other infections killed far more men than were lost in battle. Even during World War I—and despite considerable progress in medical science during four decades before the war—typhus alone was responsible for over two million deaths.
Vaccines and antibiotics have since transformed our capacity to combat these and many other conditions. In particular, the elimination of smallpox during the 1970s is rightly applauded as one of the most spectacular feats ever achieved by applied science. Thirty years ago, in light of widespread immunization, the “antibiotic revolution,” and other advances, it seemed that the conquest of dangerous viruses and bacteria was drawing to a close as a triumphant phase of human history.
Any complacency that might have existed at that time has long since been shattered by the resurgence of diseases, such as tuberculosis, which were thought to have been defeated, and by the appearance of a long catalogue of hitherto unknown or unrecognized infections. These include Campylobacter food poisoning, legionnaires’ disease, Lassa fever, Listeria food poisoning, Lyme disease, HIV/AIDS and of recent the Ebola virus. As the World Health Organization said recently: “A host of new and re-emerging diseases are now threatening the health of the world.”
There are three principal reasons to fear that, despite the unquestioned successes of the past, the future could see the emergence of an uncontrollable infection with devastating consequences for society. One is the widespread proliferation of bacteria unaffected by antibiotics, and the rapid spread of resistance (to ten or more different antibiotics) in bacterial populations.
The main explanation for the declining power of these drugs is simply that they have been used excessively, often being prescribed indiscriminately for trivial conditions. This over-use has led to the emergence of bacteria able to resist attack by antibiotics. To make matters worse, resistant bacteria can also pass on resistance (without losing it themselves) to initially sensitive bacteria.
A second reason for very serious concern about infectious disease in the future is that microorganisms are relentless opportunists. Because of their astronomical numbers, their phenomenal growth rate and their adaptability, they can often exploit new circumstances to grow and cause disease. For example, the bacterium responsible for legionnaires’ disease occurs in streams and lakes, where it has no effect on human health, but when the same microbe is released into the air as an aerosol, it can prove deadly. Breathed into the lungs, this otherwise innocuous bacterium causes a virulent type of pneumonia which is often fatal. Yet we simply did not know about this deadly possibility until the first outbreak of legionnaires’ disease occurred in Philadelphia in 1976.
One particular reason why microbes adapt so quickly to new circumstances is their considerable capacity to ferry genes between one organism and another. Not only genes responsible for drug resistance, but those bestowing many other traits too, are constantly being passed around in the microbial world.
The third source of anxiety about our vulnerability to infections is that our surveillance over the behavior of microbial populations is far from adequate, especially with regard to the monitoring of genetic changes in disease-causing organisms. At present, only a vanishingly tiny fraction of infections are properly diagnosed and the organisms identified. This means that we are simply ill-equipped to detect, let alone anticipate, potentially catastrophic changes in the microbial world, the outbreak and spread of the Ebola virus being a suitable example. Although a world network of influenza reference centers, coordinated by the WHO, provides some information about the emergence of new influenza viruses, overall the level of surveillance is not sufficient to detect as quickly as possible many other possible alterations in the microbial world.