When smallpox was eradicated in 1980, AIDS was still unknown as a cause of mortality. But in the early 1980s, outbreaks of “slim disease,” the local name for people displaying the symptoms of AIDS, were reported across much of Southern Africa.5 Only a few years later, in 1989, I spent time teaching in a school in rural Bulawayo in Zimbabwe, and all of the students were encouraged to give blood. The country was one of the first in the world to test all blood donations for HIV, and when the results of that test were passed back to a student in the school, a letter announcing positive status was an invitation to pariah status and death —there wasn’t yet any effective treatment.6
Just as the Black Death and cholera spread along trade routes, so did AIDS. The University of Chicago’s Emily Oster studied the spread of HIV in Africa and found that countries that exported more saw higher rates of infection—with HIV cases concentrated in regions with good road networks. She suggests truckers moving the export goods spread HIV at the same time.7
By 1990, AIDS was responsible for around three hundred thousand deaths worldwide a year. And in 2010, the annual death toll was 1.5 million. AIDS still kills as many people yearly as suicide, murder, manslaughter, and war combined. Especially in Sub-Saharan Africa—home to about two-thirds of the world’s AIDS sufferers—HIV was a tragic force for reversal in health and broad-based development.8 Life expectancy in some countries declined by ten years or more thanks to the disease, wiping out decades of previous progress.
Nonetheless, the annual global death toll from AIDS reached a plateau around 2005, and is falling—thanks in no small part to a growing antiretroviral drug industry in developing countries as well as the support of antiretroviral treatments from donor governments including the US.9 The progress in treatment and prevention has been dramatic, with some hope for an AIDS-free generation in the next decades. In 2013, for the first time ever, fewer people worldwide were newly infected than put on the antiretroviral drugs that keep HIV victims alive and help prevent them from infecting others.
The global response to HIV was unprecedented—too small and two decades too late, but massive and effective in comparison to previous anti-plague efforts. And progress against AIDS is one sign of why we’re in a far better place today in the battle against infection than we were fifty, five hundred, or five thousand years ago. The AIDS crisis demonstrated the risk of new threats but also highlighted the potential effectiveness of strong national health systems, research capacity, and coordinated international response to control disease.
The early stages of the Covid-19 pandemic augured a similar combination of slow reaction and opportunities missed alongside the stirrings of a historically unprecedented response. Hopefully, next time, we’ll act faster and save more lives. Because the other lesson driven home by the four decades between HIV and Covid-19 is that, thanks to expanding agriculture, dense populations, and global links, there’ll be a next time.
* * *
Evolutionary biologist Katherine Smith and colleagues at Brown University studied more than twelve thousand reported disease outbreaks worldwide since 1980 and concluded that both the number of diseases and the number of outbreaks have been increasing over time (though the good news is that the cases of illness in each outbreak have declined thanks to better surveillance, prevention, and treatment).10
Since 1970, we’ve seen the emergence of new infections, including severe acute respiratory syndrome, avian influenza, Nipah virus, Hendra virus, Ebola, Marburg fever, Lassa fever, variant Creutzfeldt-Jakob disease, cryptosporidiosis, cyclosporiasis, Whitewater Arroyo virus, hantavirus, and (of course) Covid-19. That’s not to mention resurging or reemerging diseases, including multidrug-resistant tuberculosis, monkeypox, dengue and yellow fever, drug-resistant malaria, and even plague.11
Some new diseases emerge from forests as HIV did. The 1998 Malaysian Nipah virus epidemic demonstrated how the continued spread of human activity puts us in contact with new zoonotic illness: fruit bats carrying the disease were displaced by deforestation and ended up sharing fruit with pigs crammed into large pens near orchards. As the pigs trampled the fruit bat’s droppings, they aerosolized the excrement, and breathed it in. The pigs were infected with the Nipah virus, which was then passed on to human handlers. The condition can cause swelling of the brain, coma, and death—sometimes years after exposure.12 (Covid-19 also emerged from bats.)
Other diseases mutate and evolve from the existing stock of infections that accompany people and their livestock. Humans only reproduce after more—often considerably more—than a decade and a half of growth. The average virus produces thousands of offspring in one or two days.13 That means microbes can evolve a lot faster than their hosts.14 And even minor mutations can have dramatic implications. Rapid evolution is why previously (comparatively) unthreatening infections can quickly become big killers.15
Consider, for example, another recent outbreak: in the week of April 13, 2009, two unrelated children in Southern California fell ill, coughing, sneezing, and running a temperature. Both sets of parents took them to separate clinics. Both children were tested and found to have flu of an unidentified strain. The children went home with the usual assortment of drugs and both felt better within a week. But according to standard protocols, the United States Centers for Disease Control was alerted. On April 17, four days after the children had visited clinics, the CDC declared that the children had contracted a previously unknown flu virus, swine influenza A H1N1. It was labeled swine influenza because this was a strand that had jumped species from pigs to cause illness in humans. “Concern exists that… a large proportion of the population might be susceptible to infection, and that the seasonal influenza vaccine… might not provide protection” against the swine influenza variant, reported the CDC.16
By the end of the month, the World Health Organization had declared a global pandemic of swine flu. Mexico, at the epicenter of the outbreak, reported 949 laboratory-confirmed cases, including 42 people who’d died of the disease. The country closed schools and banned large public gatherings.17 By the first week of May, a total of twenty-one countries had reported cases across Asia, Europe, and the Americas. Despite the development of a vaccine to fight the flu strain, deaths from influenza shot up—one estimate is that the pandemic caused 12,469 deaths in the US alone by April 2010.18
The risk of infection from livestock has been magnified by factory farming. While “only” 376 million pigs were slaughtered worldwide in 1961, by 2012 that number had climbed to 1.4 billion.19 And the pigs are grown in increasingly massive lots. The average pork producer in the United States owned fewer than fifty hogs in 1964. Today, that producer owns more than eleven hundred.20 Big farms that produce most of the pork and bacon we consume are a multiple of that size. It isn’t just pork: the number of chickens worldwide has climbed from 3.9 billion in 1961 to 21.7 billion today. More than three-quarters of all chicken is factory-farmed.21
Though the very existence of such farms is, in part, a sign of our success in controlling livestock disease, these operations still expand the space for viruses and bacteria to evolve new threats. Take Malaysia’s Nipah outbreak: the country saw dramatic economic growth in the 1980s, and rising incomes increased demand for meat. Malaysia’s agricultural sector scaled up massively, replacing family production with factory farming. With thousands of pigs packed into close quarters, a disease that previously jumped from bats to pigs in isolated cases multiplied in sheds of a thousand-plus hogs—and then spread to humans.
The Malaysian government responded by killing 1 million pigs in a mass cull, and Nipah retreated. But it has re-emerged across Asia since then, and it also appears to have become more deadly, killing up to 70 percent of infected pig populations and sometimes spreading directly from one human to another.22
And diseases that jump from animals to humans are far more likely to escape the farm or forest village because the world is more connected than ever before.23 A single crowded New York subway car can hold about 250 people. Through muc
h of history, the great majority of humans have lived in communities no bigger than that. And in an age before motorized transport or decent roads, many people barely left their village. We’ve seen that this tendency to stick close to home was a protection against the spread of epidemics and pandemics, including the plague.
But not even the poorest people on the planet today travel so little anymore. In 1960, there were around 122 million vehicles on the world’s road network. Today, there are about ten times as many vehicles, and the road network is far more extensive, especially in developing countries.24 With a human population at least 250 times that of four thousand years ago, some living in cities more than five hundred times the size of Ur at that time, diseases are far more likely to find new hosts before they burn out.
Over longer distances, the old mechanisms of disease spread have sped up as well: in August 1519, a flotilla of four Spanish ships under Ferdinand Magellan set off on the first circumnavigation of the globe. In September 1522, three years later, one of the ships made it back into home port. In 1873, Jules Verne published the novel Around the World in Eighty Days in which Londoner Phileas Fogg travels via Suez, Bombay, Calcutta, Hong Kong, San Francisco, and New York to arrive back home. And sixteen years later, Nellie Bly, a reporter for the New York World, actually managed the feat for real in seventy-two days. In 1976, a Pan Am 747 carried ninety-six passengers around the world in forty-six hours. Give or take, that’s one-five-hundredth of the time of the Magellan expedition.25
When tourists can travel around the world in a day or two, so can their diseases. If the origin story relating to Columbus’s crew is correct, syphilis was record-setting in the 1500s for making it from the Americas to India in only six years. Five hundred years later, microbes were taking round-the-world tours in weeks rather than years. In 2002, severe acute respiratory syndrome, or SARS, emerged in the wet markets of Guangdong Province in China, where live animals are sold to be eaten. It had jumped species from one of those animals—possibly the Himalayan civet cat.26 Three months later, a doctor from the province who’d contracted the disease spent one day in a Hong Kong hotel during which he infected sixteen guests. Three of them traveled by plane to Toronto, Singapore, and Vietnam. Within weeks the infection had reached eight thousand people in twenty-six countries across five continents.27
And in late 2019, Covid-19 may have spread via a Chinese wet market as well. On December 30, the Wuhan city government began to track cases, and on January 5, 2020, a Shanghai lab detected the cause as a novel coronavirus. The first death was recorded on January 11. By the 13th, a case was confirmed in Thailand and by the 20th there was a case in the US. By January 31, there were a total of around ten thousand reported cases in twelve countries.28
Given how many infections we share with animals, how many animal diseases may be only a few mutations away from infecting humans, and how rapidly viruses and microbes in particular can mutate and then spread in a connected world, new global pandemics will surely continue to hurl themselves at humanity.
Ronald Barrett and colleagues from the Department of Anthropology at Emory University in Atlanta have gone as far as to suggest that the emergence and re-emergence of disease threats owing to globalization and antibiotic resistance is a sign that we’re entering a “third epidemiologic transition” comparable to the rise of infection at the dawn of civilization and its fall in the last century and a half.29 That (hopefully) goes too far, but it certainly suggests the scale of the risk we need to confront. The fight against disease made our modern, urban, and connected world possible—but it didn’t remove the risk that agriculture, urbanization, and globalization have always presented when it comes to new infectious threats.
* * *
If the risk of new infection is still a major concern, so is our reaction to that risk should it emerge. Because our earliest instincts regarding infection are increasingly ill-matched to a connected world.
As we saw with smallpox in Japan, new or irregularly occurring diseases in particular can spark fear and the exclusion instinct. Flu may kill far more people every year than Ebola ever has, but unless we give a new variant a new name (swine flu, as it might be), it doesn’t raise as much concern. This may help explain why a November 2014 survey in the US ranked Ebola as the third most urgent health problem facing the country—just below the cost of healthcare and ahead of cancer and heart disease. That fear was accompanied by widespread calls for travel bans, even though there’d been only two cases of Ebola transmission inside the United States, neither of which were fatal, and all experts were saying there was little risk of spread.30
Again, we’ve seen that the exclusion instinct is based on evolutionary reality. Staying away from strangers is a rational reaction in the face of an unknown infectious threat. If it isn’t clear who is sick, the only strategy that works is to reduce contact with everyone.
Today, though, when most of the world lives in cities and only a small minority of the planet’s population is in any way self-sufficient when it comes to producing food (or anything else), total isolation simply isn’t an option. Testing and isolating the sick, along with tracing their contacts, was a successful strategy against Ebola in 2014 and against Covid in 2020. “Social distancing” was a necessary but expensive fallback in 2020 when we didn’t know who was infected.
Distancing and stay-at-home orders worked to reduce the average number of people infected by each person with Covid-19 to below one, meaning that infection rates decreased. But an early estimate of the effects of the coronavirus lockdowns on the US economy from just the one month of April 2020 suggests an average cost of $5,000 per household. (The effects were far larger for some families: more than 20 million people were thrown out of work in the US during April alone.)31
And the associated health impacts of the early coronavirus response were considerable worldwide. Those with conditions other than Covid-19 were kept away from hospitals, routine immunization programs were paralyzed, and millions were sunk into poverty where they suffered from malnourishment and the illnesses that are its by-product. Early estimates suggested that in some developing countries the response to Covid-19 might kill more than the infection itself.
Lockdowns were never designed to be a stand-alone solution. Rather, they were a short-term strategy to buy time for better strategies and to prevent hospitals from being overwhelmed by patients. And it’s worth repeating that people sensibly and instinctually want to stay away from others when there’s a new disease spreading with no cure. At the start of Covid-19’s spread, it didn’t take regulations from above for people to stop going to restaurants and cut back on shopping. But for whatever highly contagious, often asymptomatic novel infection that comes next, every country needs to be efficient at using the time provided by lockdowns to come up with less restrictive methods to slow spread and build confidence. Those methods should include mass testing and tracing that allows for selective isolation.
Notably, exclusion at the border is far more expensive and far less effective in a world based on global exchange. Quarantines and border controls probably helped reduce the spread of plague, but they proved considerably less useful against cholera and yellow fever in the nineteenth century. Today, even while isolation of the individual sick tourist can be a practical emergency strategy, and short-term travel bans may sometimes have a role to buy extra time to respond to a new pandemic, the world is simply too connected for even the greatest build-a-wall fantasist to think diseases can long be kept out by closing borders.
In 1986, for example, AIDS was added to the list of infections that would prohibit permanent entry under the US Immigration Act. Even tourists with HIV had to apply for a waiver that, if granted, involved an indelible stamp in their passport announcing to all their HIV status. This despite the fact that in 1987 the World Health Organization had concluded that screening or banning international travelers wasn’t an effective tool to reduce the HIV burden. You can tell that travel limits didn’t work to stop the spread of AIDS b
ecause it was first identified in the US (rather than in the Congo Basin) and quickly reached the countries most cut off from international travel and commerce, including Burma under the Junta.
Similarly, travel controls put in place over the H1N1 virus led to a 40 percent drop in air traffic to and from Mexico following the international alert, but had no effect on the spread of the disease. Epidemiologist Paolo Bajardi and colleagues argue that the evidence from the H1N1 outbreak suggests that even a comprehensive travel ban would, at best, have delayed the spread of the condition by twenty days.32
The limited efficacy of travel bans in the face of a frequently asymptomatic and rapidly spreading disease was on full display with Covid-19. While it’s good to avoid people congregating in airports or in airplanes as much as it is in trains or factories during efforts to reduce the spread of a disease, there’s no cross-country evidence that countries that introduced travel bans saw lower rates of coronavirus infection in the first few months of 2020.33 Early estimates of the overall impact of travel bans suggest they slowed the spread of the virus from between two to three weeks at maximum and zero days at minimum.34
The US government issued its first partial travel restrictions on January 31. In the time between the coronavirus emerging in China and the United States travel ban, 390,000 people flew from China to the US. There’s some evidence that Covid-19 may have spread during the Las Vegas Consumer Electronics Show between January 7 and 10, attended by 170,000 people.35 There was a coronavirus case in the US on the 20th of January. And there was at least one Covid-19 death in California on February 6, suggesting an infection two weeks prior.36
Even in the two-month period after the US travel ban was introduced, a further 40,000 people (including US citizens and green card holders) made the journey from China to the US.37 Worldwide, between January and early April, nearly 11 million people flew into the US from countries with confirmed cases of Covid-19.38 And the threat of wider travel bans meant that millions of people rushed home before they were enforced. That led to packed immigration and customs halls, crushing thousands of people together in a small space for many hours. Crowded terminals at JFK and Newark were likely a factor in the severity of the outbreak that hit New York City.39
The Plague Cycle Page 16
