A One Health Approach to Preventing the Next Pandemic
Instead of waiting for the next deadly microbe to spill over into humans, public health experts and policy-makers must confront the drivers of zoonotic diseases.
China and India have much in common. Both are developing countries with populations of over 1 billion. Both have live animal markets. Both have issues with public sanitation and hygiene. Both are major users of antibiotics and have severe problems with antimicrobial resistance. But China has a long tradition of people eating wild animals and using them in traditional medicines—practices that likely increase the transmission risks of microbes from animals to humans, causing what are called zoonotic diseases. In India, by contrast, 40% of people are vegetarian, the largest fraction of vegetarians of any country. India certainly has its share of infectious disease problems, but it has not suffered coronavirus spillover events from wild animals the way China has. Examining the origins of recent pandemics sheds light on why this may be the case.
Although the precise transmission of the novel coronavirus that causes COVID-19 from animals to human is unclear, scientists generally agree that the pandemic originated in China. The earliest inkling of a new coronavirus was posted on December 30, 2019, on a global online disease surveillance system called the Program for Monitoring Emerging Diseases, or ProMED, run by the International Society of Infectious Diseases. Four individuals with unusual pneumonias unresponsive to antibiotics were hospitalized in the city of Wuhan. The first patient with the unexplained pneumonia had reportedly visited a wholesale seafood market in Wuhan, the largest live animal market in central China. The symptoms of these early patients suggested a coronavirus, a family of viruses that cause respiratory tract illnesses, including the common cold. The serious symptoms of this novel coronavirus raised alarm bells for public health officials.
The beginning of this pandemic is reminiscent of another disease caused by a coronavirus, severe acute respiratory syndrome (SARS), which also originated in a live animal market in China. A chef who regularly cooked with exotic animals was one of the earliest persons to be diagnosed with SARS. He subsequently infected his wife, sisters, and health care workers. Ultimately, SARS infected more than 8,000 people and killed 774 of them. Epidemiologists believe that SARS is less easily transmitted but more deadly than the novel coronavirus.
Genomic studies suggest that Rhinolophus affinis (Chinese horseshoe) bats are the reservoir host species for the SARS and COVID-19 viruses. It appears that these coronaviruses spread to people through intermediate animal hosts. In the case of SARS, civet cats were the intermediate hosts. Pangolins, which are scaly anteaters, may be the intermediate hosts for the new coronavirus, named SARS-CoV-2. Highly coveted for food and traditional medicines, pangolins are the most heavily trafficked mammal in the world.
A coronavirus is also responsible for causing the Middle East respiratory syndrome (MERS). But researchers believe MERS originated with either Tylonycteris or Pipistrellus bats, with domesticated dromedary camels serving as intermediate hosts. MERS viral genomic studies suggest that the virus is endemic to camels in Saudi Arabia. Domesticated dromedary camels are an integral part of Saudi Arabian culture and have been used as beasts of burden and for meat and milk products for centuries. Similar to SARS and COVID-19, the MERS coronavirus causes primarily respiratory illnesses including fever, cough, shortness of breath, and pneumonia. With a mortality rate estimated at nearly 35%, MERS is much deadlier than its coronavirus cousins, but more difficult to contract. For MERS, the initial camel-to-human transmission appears to have occurred via nasal secretions from four sick camels.
The common element between SARS, MERS, and COVID-19 is close human contact, including consumption, with wild or domesticated animals. This isn’t a new phenomenon; these risks have existed since the dawn of animal domestication. Today, three-quarters of new or emerging infectious diseases are zoonotic.
But instead of conducting microbial surveillance in animals, particularly wild animals, and prohibiting the sale of those harboring potentially dangerous microbes, public health experts and other policy-makers wait until after deadly microbes spill over into humans before acting. If experts had been paying attention, they may have been able to prevent zoonotic disease spillover events such as SARS and COVID-19. Instead, policy-makers rush around putting out viral fires after they’ve spread. Society’s approach to public health needs to proceed strategically, not reactively, if humans are to sustainably meet dietary needs for meat and other animal proteins. Human health is tied to the health of animals and the environment. This means society will need to recognize the inextricable links between human, animal, and environmental health, and it will require sharper examination of humans’ relationship with and consumption of domesticated and wild animals in order to reduce zoonotic disease risks. The One Health Initiative focuses on these goals.
Meat and other animal proteins are important sources of essential micronutrients, and eating meat is an integral part of many cultures and religions. Global demand for meat and other animal proteins has been increasing, and to meet demand, global production has been increasing as well. The world’s population of nearly 8 billion people maintains roughly 30 billion food animals. People and their domesticated animals produce an estimated 4 trillion kilograms of fecal matter each year, with animals accounting for about 80% of it. (A back-of-the-envelope calculation estimates that all this fecal matter would fill 1.6 million Olympic-sized swimming pools each year.) Most manure is applied as fertilizer to agricultural fields, where it mixes with the soil microbes. This fecal matter can contaminate crops, streams, and coastal waters contributing to foodborne and waterborne diseases. Making matters worse, antibiotic use in intensive animal farming gives rise to antibiotic-resistant bacteria, which also pose a major public health challenge. In short, raising animals for food in enormous quantities is changing the planet’s microbial ecosystems in profound and potentially dangerous ways.
Americans eat more meat per capita than any other nation, and are in no moral position to tell people in other countries what they can or cannot eat. Including such iconic meals as Thanksgiving turkeys and Fourth of July hot dogs and hamburgers, meat is an important part of American culture. It is unrealistic to expect Americans or the rest of the world’s population to become vegetarian. However, that doesn’t mean that people shouldn’t reduce their meat consumption. Many people live perfectly healthy lives as vegetarians or vegans as long as they supplement their diets with vitamin B12 and other primarily meat-derived nutrients. It’s possible that large populations of vegetarians or vegans might even reduce zoonotic disease spillover risks, as the comparison of China and India indicates.
So what can be done to prevent the next zoonotic pandemic?
The One Health model provides a strategy. Researchers must examine the human, animal, and environmental components of zoonotic spillover events before they can effectively address them. The most profound way that humans interact with the environment is by eating it—in this case, in the form of animal protein. Although it’s unrealistic to expect the United States or other nations to become vegetarian or vegan, there are ways to reduce animal protein consumption. For example, plant-based meat alternatives are now available. Although many people consider the newest of these products more palatable than earlier iterations, they are expensive and unlikely to replace animal-derived meat products any time soon. Laboratory-grown, cell-based meat provides meat without the animals. These products are currently in research and development, and it’s unclear if they will ever be affordable or desirable to the general public.
Two billion people around the world eat insects. Insects provide high-quality protein and vitamins, are extremely efficient, and need very little feed or space. They produce minimal waste and emit much less greenhouse gases than livestock. They would be a perfect solution, except for one important thing—the “ick” factor. In affluent countries, insects are viewed with revulsion, with one exception: lobsters. As “insects-of-the sea,” lobsters were once viewed as vermin and fed to prisoners. That sentiment changed slowly. By the mid-twentieth century, lobsters became gourmet food and cost top dollar. With clever advertising, edible insects have the potential to become fashionable too.
Much has been written about the need to reduce the wild animal trade for food and other products. Many such animals, including pangolins, coveted for their meat and scales, have become extremely endangered. To counteract problems, some observers have suggested banning wildlife trade entirely. But the problem with banning trade is that it goes underground as long as demand remains, making surveillance and control of zoonotic pathogens even more difficult. Changing culture and demand is more difficult, but in the long run provides a much more effective strategy than the alternative, as the world is discovering with COVID-19.
In addition to society’s efforts to reduce global demand for animal protein, scientists and pharmaceutical companies need to rapidly develop and produce antimicrobials against zoonotic bacteria and viruses. Antimicrobial resistance is a worsening global problem. The pipeline to develop new antibiotics has dwindled to a trickle for a variety of reasons, including the lack of pharmaceutical industry interest and the high R&D costs. Since 1963, the US Food and Drug Administration has approved 90 antiviral drugs for nine diseases. Of these diseases, however, only HIV and influenza have known zoonotic spillover origins. A boost in R&D funding for antivirals from public and private sources is likely, but this must be maintained even after the COVID-19 crisis has been addressed.
Another important component of preventing zoonotic disease transmission is through vaccines. Depending on the microbe’s reproductive lifecycle, three preventive strategies could be used: vaccinating both humans and domesticated animals, vaccinating only domesticated animals, or vaccinating wild animal reservoirs. The key to success, of course, is widespread political and public support for the development and use of these vaccines. In the case of COVID-19, vaccinating animals to prevent spillover events might be a tougher sell than vaccinating people after a spillover event has already occurred.
Finally, and perhaps most importantly, societies need to improve global sanitation and hygiene. This is particularly important for the fecal matter produced by domesticated animals. In many countries, animals live in close proximity to humans and share their microbes with people. Developed countries manage livestock manure, but developing countries often do not. Technologies such as methane digesters, which collect methane from fecal matter and convert it to biogas, can be important in reducing the environmental impact of global manure production. They may help to incentivize better management of manure. More innovative technologies targeting fecal waste are needed.
In essence, a One Health approach focuses on the upstream drivers of potential zoonotic diseases to prevent spillover events from occurring. It includes microbial surveillance of animals and vaccines for domesticated animals to reduce their risk of acquiring diseases from wildlife. It includes efforts to reduce deforestation and other human activities that are destroying wildlife habitats. Reducing human contact with wildlife reduces opportunities for microbial transmission.
We live in a microbial world. We inhale microbes. We eat microbes. The sooner we figure out how to meet our nutritional needs while preventing deadly zoonotic microbes from infecting us, the better off we’ll be.