Francesca Tomasi received her B.A. from the University of Chicago in 2015 and currently does microbiology research.
I took a History in Philosophy and Science course in college that examined the birth and evolution of medicine. Just as most history classes go, our professor started us off with ancient texts and we worked our way through the centuries into modern literature. We raised eyebrows at the claims that pestilence was a form of divine intervention and that the plague discriminately infected only those who sinned. We chuckled sagaciously at Aristotle and Hippocrates, who proposed that illness had only to do with a discordance between the four humours in our bodies (blood, phlegm, black bile, and yellow bile). Our professor told us we were wrong to laugh, though; as naïve as ancient thinkers were to the intricacies of the human body, they actually had an impressive grasp on the big picture. Hippocrates in fact predicted that public health was contingent on environmental factors around 400 BCE. 2000 years later, an Italian physician named Giovanni Maria Lancisi propagated the idea that humans, animals, and the environment are inextricably linked (amongst other major medical contributions, he proposed the use of mosquito nets as malaria prevention). During the French Revolution about a century later, public hygiene became practice and health less of an exception and more of a rule in communities. By the turn of the 20th century, the term “zoonosis” was coined by the Germans: diseases could (and often did) arise from animals infecting humans.
One hundred years later in 2003, the Washington Post published an article titled Africa’s Apes Are Imperiled, Researchers Warn. The third paragraph gives the overt cause: “With hunters venturing ever deeper into the forest along newly cut logging roads, and the Ebola virus poised to sweep into parks…disaster is close at hand.” Ebola was a dangerous hemorrhagic fever to apes well before it spilled into humans. A decade before the Ebola epidemic in West Africa, scientists were scrambling to slow the virus’s spread, “in large part because they don’t know whether it is passed only from ape to ape or via other animals,” according to the Washington Post. The link between man and ape then became increasingly immutable as demand for food, land, and work went up. Today we know at least part of the answer to a question posed in 2003. Yes, Ebola is spread from and amongst various mammals: non-human primates, bats, and humans. In this case, as is the case with many other diseases, the health of one species is no longer independent of the health of another. The Washington Post article ended with an augury whose words bear this very implication. William Karesh, head of the field veterinary program of the Wildlife Conservation Society, was quoted: “Human or livestock or wildlife can’t be discussed in isolation anymore. There is just one health. And the solutions require everyone working together on all the different levels.”
Modern health issues have been linked time and again to the increasing contact (and intensification thereof) between humans and animals. Changes in land use (such as the deforestation described in the Washington Post article), large-scale emissions, and massive food production units are all significant environmental changes with substantial health impacts. The twentieth century saw an alarming surge in emerging infections that were rapidly attributed to zoonoses. International travel and globalization as a whole only made it easier for an emerging infection that 100 years ago would have been confined to a single region to infiltrate any pocket of the globe. According to a literature review published in 2001, there are at least 1,415 species of infectious agents known to be pathogenic to humans (this number is likely higher now). Of these, 868 are transmitted between animals and humans: about 61 percent of known human infectious diseases have been linked to animals. The authors of this study also examined 175 emerging infections at the time and found that 132 (75%) of them were zoonotic. The conclusion? “Overall, zoonotic pathogens are twice as likely to be associated with emerging diseases than non-zoonotic pathogens.” What would the conclusions of a similar analysis have been a century earlier? Five centuries? A thousand years ago? Scientists would not have been aware of the vast majority of these pathogens, by virtue of the fact that they would still have been confined deep in the throes of Mother Nature’s most species-rich and isolated rainforests. But today, we know that rodents brought about the bouts of Plague that inundated the Middle Ages. We know that measles, mumps, and pertussis arose from the domestication of livestock. We know that HIV came from chimpanzees. A 1999 outbreak of West Nile virus in New York City killed off wild crows about a month before people started getting ill, yet it was the same exact infectious agent that ultimately sickened both species. We know the flu is a disease of birds, pigs, and people, and that the interactions between these three species are what bring about novel flu strains every year – some more dangerous than others.
None of this would be known today if it weren’t for the marriage of multiple fields: human medicine, veterinary medicine, ecology, and environmental studies. Partnerships between doctors, veterinarians, ecologists, and epidemiologists are exactly what brought about the commissioning of the One Health initiative in 2007. One Health seems a campaign inevitable in the 21st century, but it’s really a concept that has been millennia in the making, starting with the Greeks observing a relationship between people’s environment and their well-being. One Health is “a worldwide strategy for expanding interdisciplinary collaborations and communications in all aspects of health care for humans, animals, and the environment.” It goes without saying that such a synergism will “accelerate biomedical research discoveries, [enhance] public health efficacy…and [improve] medical education and clinical care.” There are now over 1000 scientists, physicians, and veterinarians around the world who have endorsed One Health. In addition, countless organizations – from the CDC to the National Oceanic and Atmospheric Administration to the European Union – support it. The World Bank in 2012 published a cost-effectiveness study of a One Health approach to global health, concluding that the “early control of zoonotic disease is both cost-effective and prevents human disease.”
I am writing this article with my beautiful cat Charlotte purring contentedly by my side, blissfully unaware of the fact that her health and mine are in fact inextricably connected. Her ancestors and mine didn’t share a roof; ancient humans would be hard-pressed to kiss a feline’s head, let alone share their pillow with a cat. Yet here we are today, two species sharing a couch, propagating each other’s mental and physical health. One Health. It bears a vague resemblance to the ancient Greek idea that illness comes from disharmony between four distinct humours within our bodies. But instead of phlegm, bile, and blood, the humours are animals, humans, and the environment. The body is Earth. In college, we found humor in the humours. The fact of the matter, however, is that the Greeks get the final laugh.