Over the course of the next year an American is more likely to die from a car accident (1 in 9,100), a shark attack (1 in 3.7 million), a bee sting (1 in 5.2 million), a lightning strike (1 in 9.6 million) or a plane crash (1 in 11 million) than from Ebola (1 in 13.3 million).
Why do we continue to experience such an exaggerated fear of Ebola here in the United States?
Why do many support measures that could worsen the problem, such as closing our borders or imposing quarantines on returning health care workers?
Why, despite constant media coverage, do so many people seem not to understand the key facts about Ebola transmission?
The answers to these questions relate to an immune system most people have never heard of. An understanding of this protective biology could inform how we might respond to the Ebola epidemic more successfully.
Humans are highly social animals. Given the physical superiority of our predators, survival depended on it. However, group living was a mixed blessing. The safety afforded by living in close proximity came with the dangers of physical attack and contagious disease.
The capacity to detect risk and respond in a way that maximizes survival is an essential talent. Evolutionary pressures therefore favored both a desire for affiliation and a capacity to identify potentially threatening characteristics in our neighbors. Like many danger detecting systems, it is biased in a risk-averse manner erring toward caution.
Thousands of years of adaptation have provided contemporary humans with a hardwired infectious disease threat management system composed of two divisions. I will call one the biological immune system (the body's cellular response to infection) and the other, the less familiar, behavioral immune system. Unlike the biological immune system that kicks in after an infectious agent has invaded our bodies, the behavioral immune system functions to avoid the possibility of infection.
Emotions play a central role in any human precautionary system. We are exquisitely attuned to people exhibiting perceptible cues of possible infection such as excessive sweating, skin lesions, vomiting and diarrhea. Not surprisingly, research has consistently demonstrated that threats to our physical safety elicit fear and the sight of diseased people triggers disgust. These emotions mobilize an adaptive reaction on multiple levels. There is not only the behavioral response of distancing oneself from the sick, but a cellular one in which white blood cells become more reactive to bacterial infection.
Certain factors can amplify these signal emotions. Categories of people who are unfamiliar (strangers and foreigners) are more likely to elicit these defensive feelings. This has given rise to the long-held perception of infectious disease as a problem caused by outsiders. Such heightened vigilance can breed xenophobia.
Syphilis provides an amusing case in point. It was called the French disease in Italy, Poland and Germany, the Italian disease in France, the Spanish disease in Holland, the Polish disease in Russia, the Christian disease by the Turks and the British disease by the Tahitians. The more distant the origin of a malady and the more exotic the name, the greater the emotional response it generates. And this intensified emotion drives more extreme avoidance behaviors.
In addition, anything that increases a sense of vulnerability boosts the behavioral immune response. The imagery provided by the 24/7 media scores a bull's eye for this system. Victims, wet with fever, are viewed as the life literally pours out of them in blood, diarrhea and vomit. Health care workers shrouded in Hazmat suits, like astronauts on a distant planet, could not appear more alien.
So Ebola provides the perfect scenario for a maximal behavioral immune response. The exotic name, far away origins, outsider populations, conspicuously ill victims and extreme lethality all play a part. Unfortunately, like many hard-wired pychobilological systems, it can produce maladaptive behavior. This is due in large part to differences between our contemporary environment and the one in which the behavioral immune system evolved.
The immune system is the body's homeland security. Its most fundamental function is to distinguish between self and other. Immunology is all about identity. The mission is to destroy what is foreign. The language of immunology is martial, illness as war. We fight infection, mobilize defense systems, develop a resistance, and seal off the "foreign body" (the medical term for anything found in an organ or tissue in which it does not belong under normal circumstances).
Historically, epidemics have accompanied war. Until the Second World War more victims of war died of war-borne microbes than of battle wounds. The victors were not always the armies with the best generals and weapons but often those bearing the nastiest germs to transmit to their enemies.
Tolerance, in the immunology realm, refers to not attacking potential targets allowing some foreign elements an adopted equal status within the organism. Recent research on the microbiome (the bacteria living in our gut) has demonstrated the importance of such foreign populations that reside within us. This symbiotic relationship is essential to our health.
The opposite of tolerance in the immunological world is autoimmunity. Here the immune system misidentifies self as other and turns on itself. This provides a fitting metaphor for what we are doing when we think of Ebola as the problem of others.
Much of our survival as a species can be attributed to biologically evolved threat management systems. This wiring directs events from the cellular to the cultural level. The desire to seal off borders and quarantine the health care workers is driven to a large extent by our ancestral behavioral immune system. Cues that once improved survival have become maladaptive behaviors in our contemporary world.
Ebola is the ultimate demonstration of globalization. Our species originated in Africa. Our ancestors' exodus from that continent brought human life to every conceivable habitat and gave birth to the remarkable diversity of our species. Despite differences of appearance, belief and behavior, we are all part of an extended African family. And modern life has obliterated the distances that once separated this family's members.
To prevent further Ebola losses our energy and resources might best be directed to helping our African brothers and sisters, not isolating them and those who help them. They are us. In the modern world, serious infectious disease in one population is everyone's problem. If homo sapiens (the wise man species) are to survive, we will need the wisdom to overcome aspects of our biology that got us this far.