How History Can Help Us Understand and Cope With COVID-19

Throughout history, we have gotten many diseases from animals. Here are lessons.

Posted Apr 10, 2020

Why bats?

Over the centuries, humans have acquired scores of infectious diseases from other species. COVID-19 is the latest. 

Rodents gave us 32 disorders (most famously bubonic plague), pigs 42 (including influenza), horses 35, sheep and goats 46, cattle 50, dogs 54 (including rabies and ringworm), and poultry 26. Coronaviruses, including SARS and now COVID-19, live in bats. COVID-19 probably leaped from these winged mammals to humans via an intermediary species, such as pangolins.

As humans progressively domesticated and interacted with animals, we acquired new infections that then altered civilizations. Every microbe has a "natural reservoir"—one or more species in which it lives in balance. In these natural habitats, these bacterias and viruses thrive in healthy and harmonious synergy, generally without causing disease—what scientists call symbiosis. The human gut, for instance, nourishes billions of E. coli bacteria, digesting our food for us into more basic proteins and sugars that we can then absorb.

Any microbe that kills all its natural hosts would lose its comfortable niche and go extinct. To persist, infectious agents need one or more species they can inhabit without destroying. Over time, these hosts have usually developed an immunity.

Yet when different species suddenly interact closely outside of the natural habitats in which they've evolved over millions of years, their microbes can leap between them and cause so-called zoonotic disease. Eventually, members of the new host species develop resistance or go extinct.

Smallpox, for instance, results from variola viruses that turn out to have a natural reservoir in rodents and occasionally infect cows, causing cowpox, which then mutated and spread to humans, causing smallpox. Several thousand years ago, after Indo-Europeans domesticated cows, smallpox epidemics erupted, periodically ravaging humanity, killing 35 percent of patients and permanently scarring survivors' faces.

In 1492, when Columbus and his Spanish crews entered the Caribbean, they brought smallpox with them. Native populations, never having been exposed to cows and thus to this disease, lacked immunity. The microbe quickly decimated villages and cities, racing along indigenous trading roads, including those that stretched from the Caribbean coast down the Andes Mountains into Peru. By the time Spanish explorer Francisco Pizarro reached Peru in 1531, roughly 40 years after Columbus, smallpox had killed both the Incan king and his heir, causing civil war, weakening the empire. Pizzaro, with his ragged army of only 180 men, thus had little difficulty conquering one of the greatest civilizations the Earth had yet seen.

In 1798, the British physician Edward Jenner and others noticed that milkmaids got blisters on their hands touching pustules on cows' udders, but had pure complexions, never acquiring smallpox. Jenner took pus from a milkmaid's hand and injected it into a small boy. Two weeks later, Jenner inoculated the boy with smallpox and discovered that the child was now immune. Since the Latin word for cow is Vacca, and cowpox is vaccinia, Jenner dubbed this new procedure vaccination—the term now, of course, applies when this process is used to prevent other diseases as well.

Over the centuries, wars and trade disseminated pathogens between far-flung populations, causing recurrent plagues. Eventually, however, these microbes spread to all interconnected regions. Over the past few centuries, scientists in many countries—the U.S., Canada, Europe, Japan, Australia, Korea, and elsewhere—worked together, sharing ideas and data to conquer many ailments. Governments and military-backed leaders supported science in new ways.

As an example, after the French abandoned their efforts to build the Panama Canal due to workers' deaths from malaria and yellow fever, the U.S. government and military took on the task, devoting enormous resources to studying and then combatting these diseases. By the 1970s, effective antibiotics and vaccines against polio, measles, and other diseases were discovered. Humanity had conquered or survived these infectious enemies. Many leading physicians boasted that the Age of Infectious Disease was over, and the field of infectious diseases lost prestige.  

Yet in the 1980s, HIV emerged, followed by Mad Cow disease, Avian Flu, extremely resistant tuberculosis, SARS, MERS, and now COVID-19.

What happened to cause these new zoonoses? New technologies provided additional ways for germs to pass between species. Around 1950, Belgian doctors introduced hypodermic needles into the Congo to deliver newly available antibiotics. But physicians had limited numbers of needles and therefore reused them without cleaning them. African monkeys turn out to harbor a microbe that, around the 1920s, jumped to a human—probably a hunter cutting and eating a chimpanzee. The virus, now known as simian immunodeficiency virus (SIV), mutated slightly to become human immunodeficiency virus (HIV). Around 1950, a doctor stuck a needle into a patient with HIV and into other people, spreading the virus. Eventually, HIV infected over 40 million people worldwide and continues to spread.

Technological developments outside of medicine can also spread microbes between species. In the 1970s, large corporations began industrializing meat production, replacing small cattle farmers. To cut costs, factories began grinding up and chemically processing sheep bones and leftover scraps as cattle feed, for protein. The price of beef soon dropped 50 percent.

But sheep harbor small infectious proteins called prions that sometimes cause a fatal disease called scrapie. In the 1980s, following a chemical explosion in such a processing plant, Prime Minister Margaret Thatcher lowered regulations governing the chemical processing. Sheep scraps containing scrapie were then fed to the cattle, who for the first time then developed bovine spongiform encephalopathy or Mad Cow disease. Hundreds of humans ate beef from these cows and died. 

With COVID-19, technological changes disseminated a virus once it jumped species. The Chinese have long prized and eaten exotic species and used parts of them in traditional medicine. But for millennia, Wuhan, China, where COVID-19 appears to have hopped from pangolins to people in a wet market, was relatively isolated from the rest of the world. In the past 20 years, however, as China has grown as an economic superpower, more of its population has become middle class and able to travel. In 2016, over 20 million passengers flew in and out of Wuhan—along with their pathogens.

What should we do about such inter-species leaps? We can't reverse time and interact less with these varied animals, but should better prepare ourselves for inevitabilities such as COVID-19. Modern science now gives us tools, but we need to use them better—as early and preemptively as possible.

After SARS, researchers observed that bats harbored additional strains of coronaviruses that also had abilities to attack human cells. It was only a matter of time before these microbes did so. But governments ignored the threat and did not fund research to develop vaccines.  

The kind of cooperation between scientists that helped humanity in most of the last century is currently under threat. The Chinese government, for instance, now refuses to allow genetic data from any of its citizens to leave the country. Crucial information is unavailable to outside researchers regarding whether certain people's genetics make them more susceptible to this new plague or provides invulnerability—the kind of phenomenon Edward Jenner observed. Such information could help in developing treatments and vaccines and targeting preventative lockdowns throughout the world.

Over the past 30 years, corporations have also replaced governments as the main funders of biomedical research, but are also increasingly refusing to share patients' genetic and other data, seeing this information as strictly proprietary and putting profits first. Unfortunately, many not-for-profit hospitals and academic institutions, too, are now selling their patients' information to companies, which then hawk it.

History illuminates how epidemics transcend national borders and are social, cultural, and political, not just medical events, and must be seen as such. Humans have defeated microbes in the past through bravery and close international collaboration. Efforts to conquer COVID-19, too, could potentially bring us together, uniting us as a species. But we need to work to learn these lessons of history soon, certainly before the next microbe jumps from its natural hosts to us, as it surely will.