Solving the Emerging Infectious Disease Crisis*

Abstract

Today I speak to you as a witness from ‘‘ground zero’’ of the biodiversity crisis. I bring an urgent message. The human population grows daily, it’s on the move, and it’s carving a deep technological footprint on this planet. We alter landscapes and perturb ecosystems, inserting ourselves and other species into novel regions of the world, leading to potentially irreversible changes in the biosphere. This is not news. Half a century ago, Charles Elton, a founder of modern ecology, wrote, ‘‘We must make no mistake; we are seeing one of the greatest historical convulsions in the world’s fauna and flora.’’ We are also in the midst of an epidemiological crisis. Climate change alters movements and geographic distributions for myriad species. Transportation of people and goods carries countless pathogens around the globe. This brings isolated species into sudden contact. Pathogens encounter hosts with no resistance and no time to evolve any. This is also not news: Maladies rare or unknown 2 or 3 decades ago, like HIV (human immunodeficiency virus) and Ebola, West Nile virus and avian influenza, have become commonplace. In such a world—this world—events like these are ongoing. Scarcely a week passes without news of some freshly discovered strain of pathogen trading up to a human host...or bald eagles...or crop plants...or sea anemones. This is the crisis of emerging infectious disease (EID). We think of EID as isolated events, and we react only after the fact. We allocate massive resources to pathogens that have already made themselves known, while ignoring the far greater threat posed by those waiting in the wings. The ones we know are just the tip of the iceberg:—80–90% percent of the world’s pathogens haven’t been discovered yet. They’re discovering us easily enough—weekly outbreaks and endlessly mutating strains of recent years are ample evidence of that. This succession of crises is the new status quo. They’re far better at finding us than we have been at finding them. Why? The current EID crisis is a new manifestation of an old and repeating phenomenon. The rules have not changed. Every episode of global climate change and ecological perturbation throughout Earth history has produced new pathogens. More than a million years ago, our African ancestors moved from forest to savannah. Adopting a predatory lifestyle, sharing prey with grassland carnivores, early humans acquired pathogens previously found in hyenas, large cats, and African hunting dogs. They carried those pathogens out of Africa, where they added native hosts in new environments, while native pathogens returned the favor, infecting the newly arrived humans. Agriculture and urbanization brought people and animals into even closer contact, making infection and transmission easier than ever. In the past 100,000 yr, agriculture, domestication, and urbanization have disseminated EID risk on a global scale. If doctors had existed in those times, they would have remarked on a worrisome surge in the number of EIDs, responding to the crisis as best they could, after the fact. In the past 50 yr, exploding human population, rapid transit, and climate change have produced the real-time crisis you see on television daily. The EID crisis is a medical issue in only a superficial sense. It’s more fundamentally an evolutionary and ecological issue, a predictable consequence of separated species brought into close contact. The difference today is that human activity accelerates the rate of introductions, so outbreaks occur more frequently and over a wider geographic range than ever before. The potential for EID is a ‘‘built-in feature’’ of evolution. Research shows that those species best at surviving climate change will be the primary sources of EID. Pathogens are not only good at finding us, they are really good at surviving. There are many, not a few, evolutionary ‘‘accidents waiting to happen’’ out there, requiring only the catalyst of climate change, species introductions, and the intrusion of humans into areas they have never inhabited before. All of these are happening right now. * Speech given in acceptance of the Helminthological Society of Washington’s 2012 Anniversary Award. Comp. Parasitol. 81(2), 2014, pp. 152–154