Wuhan’s coronavirus, now officially called COVID-19, reveals how vulnerable humanity remains to virulent pathogens. A century after the devastating Spanish flu pandemic, public health officials are scrambling to prevent the latter plague – which has infected more than 79,000 people in at least 29 countries, most in China since February 24 – from becoming a other pandemic. As they do so, it is worth taking a step back to consider the stubborn resistance of infectious disease. Far from being an anomaly, this outbreak is the shape of things to come.
Humanity is currently experiencing its fourth major wave of infectious diseases. The first coincided with the agricultural revolution about 10 millennia ago. A more sedentary lifestyle, a greater population density, a greater proximity to domestic animals and the appearance of parasitic species such as rodents and insects in human settlements have allowed more pathogens to jump between species. A second great wave began during classical antiquity and lasted throughout the Middle Ages, as commercial and military contacts between the main centers of civilization exposed previously isolated societies to new diseases and created new vectors – rats, fleas – that spread pestilence in the Mediterranean and Asia. Between the fourteenth and seventeenth centuries alone, over 200 million people died of bubonic plague. The third phase took place after 1500, when explorers, conquerors and colonists from Europe brought new pathogens to the Americas, Africa and Australasia, and sometimes returned again, with devastating results.
Today, development and globalization are driving a new era of infectious diseases. Since 1980, scientists have discovered new human pathogens at a rate of over three per year. Almost three quarters are viruses and the vast majority are zoonoses, or diseases that jump from one animal tank to another, often recombining DNA along the way. As humans exploit and destroy once isolated ecosystems, they and their servants inevitably come into close contact with the wild species and new pathogens they host. Recent viruses that have affected humans from animals include HIV / AIDS (chimpanzees and mangabeys), Marburg (bats), Ebola (bats), hantavirus (mice), Nipah virus (bats, pigs), H5N1 (birds wild), H1N1 (pigs), SARS (bats, palm civets), MERS (camels), West Nile (wild birds, horses), Zika (monkeys and rodents), and now COVID-19 (bats). The booming trade in food for wildlife often sees the sale of more living species in the immediate vicinity, such as in the Wuhan market where COVID-19 take-off is suspected, increasing the opportunities for viral exchanges.
Humans are not simply taking advantage of new ecosystems, obviously. We travel the world in record numbers and at unprecedented speeds, potentially bringing new diseases with us. In 2017, more than 20,000 cities were connected by regular air service and the total number of air passengers exceeded 4 billion, a figure that is expected to double by 2037. The arrivals of international tourists, meanwhile, have risen 56 times since 1950, from 25 million to 1.4 billion in 2018. The speed and complexity of modern transport has eliminated geographical distance as a barrier to disease. A decade ago, most experts, including yours, predicted that Ebola outbreaks would continue to explode in remote places without endangering global health. The 2014 epidemic in West Africa, which killed over 11,000 people in mainly urban contexts and which could easily have spread by plane, concluded this comfortable hypothesis.
The increase in human mobility, as well as the dependence of the global economy on complex supply chains, puts public officials in a terrible situation, complicating the drawbridge strategy that companies have historically used to control epidemics. In Boccaccio’s “Decameron”, a group of 14th century noble men and women turn their yarns outside Florence, waiting for a plague in the city to loosen. The same word “quarantine” is of Italian origin, indicating the forty days:cuaranta days—That a ship arriving from an infected port had to sit at anchor before its passengers disembarked.
The more we invade and transform the planet’s ecosystems, the greater the chances that we will unknowingly return home with a microbial carryover.
Today, the World Health Organization advises member states of the United Nations against severe trade and travel restrictions, considering them expensive and counterproductive in preventing the transmission of infectious diseases. Few governments seem to listen. In an effort to stop the disease, China has imposed draconian policies, with travel blocks and travel restrictions affecting at least 760 million citizens, more than half of its population. Meanwhile, over 50 countries have restricted travel from China, including Russia, which banned all Chinese citizens from entering the country last week.
Beyond pure panic, scientific uncertainty is guiding these steps. The overall risk posed by any particular pathogen, including COVID-19, is a function of virulence, ease and speed of transmission. Infectious diseases with the greatest pandemic potential are those that spread easily and quickly, have a silent incubation period and kill most of those they infect. The Spanish flu pandemic of 1918-1919 affected the trifecta, affecting around 500 million people, or nearly a third of the world’s population, and caused a decline in life expectancy worldwide of nearly 10 years. It remains the greatest epidemiological catastrophe of modern times, accomplishing in one year what the Death Star did during the entire fourteenth century and what the HIV / AIDS pandemic moved slowly in its first 25 years.
While scientists are still studying the epidemiology of COVID-19, what they have learned so far is at least somewhat reassuring. The most relevant comparison is with severe acute respiratory syndrome (SARS), a previous coronavirus that emerged in southern China’s Guangdong province in November 2002, which eventually infected over 8,000 people in 17 countries. Although COVID-19 has already killed at least 2,623 people, more than triple the 779 deaths from SARS, its mortality appears to be significantly lower, perhaps 2 percent instead of 10 percent. The bad news is that COVID-19 seems to spread more easily, with early estimates suggesting that it produces an average of two secondary infections per initial infection, roughly the reverse of SARS.
As my colleague Tom Bollyky points out in his indispensable book, “The plagues and the paradox of progress”, humanity has made great strides in the fight against infectious diseases. Modern sanitation, widespread immunization and disease-specific interventions have reduced mortality rates, particularly for infants and children, reducing the almost unimaginable suffering that had been part of the human condition since time immemorial. Increasingly, the global burden of disease, even in developing countries, is made up of non-communicable afflictions of relative turnout, such as diabetes and heart disease.
However, this coronavirus outbreak reminds us that humanity’s evolutionary struggle with infectious diseases is far from over. Nature seems to have an endless supply of viral surprises to throw. The more we invade and transform the ecosystems of the planet and expose ourselves to wild species, the greater the possibility that we will unknowingly return home with a microbial carryover.
Stewart Patrick is James H. Binger, senior member of the Council on Foreign Relations and author of “The Sovereignty Wars: Reconciling America with the world” (Brookings Press: 2018). His weekly WPR address book appears every Monday.