How Humans Cause Pandemics and How to Stop Them

Dr. Michael Greger explains how humans contribute to viral outbreaks and what we can do to prevent the spread of deadly diseases in the future.

Michael Greger, MD FACLM
6-minute read
survive a pandemic

QDT interviewed Dr. Michael Greger, M.D., to gain insights from his upcoming book, How to Survive a Pandemic, available now in audiobook format.

How coronavirus outbreaks happen

Where did the SARS-CoV-2 outbreak originate?

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Ground zero for the COVID-19 pandemic was the Hua’nan Market in Wuhan, China, to which most of the first human cases could be traced. First thought to be a SARS-coronavirus, it was found to be a virus later named SARS coronavirus 2 (SARS-CoV-2). It's the cause of coronavirus disease 2019, or COVID-19. Before it became known as SARS-CoV-2, however, it was known as the Wuhan seafood market pneumonia virus.

Described as the largest wholesale seafood market in Central China, the Hua’nan Market reportedly also sold seventy-five species of wild animals. Although there are fish coronaviruses, more than 90 percent of the samples that turned up positive for the virus were found in the section of the half-million-square-foot seafood market that trafficked in exotic animals sold for food.

The current theory is that COVID-19 originated in bats before jumping to humans after passing through an intermediate host, thought to be the pangolin. Between the demand for their meat as a delicacy and their scales for use in traditional medicines, pangolins are the most trafficked mammal in the world. Coronaviruses found in two different groups of diseased pangolins being smuggled into China were found to be about 90 percent identical with the COVID-19 virus. As well, the pangolin coronavirus spike protein’s critical receptor binding region is virtually identical to the human strain.

The current theory is that COVID-19 originated in bats before jumping to humans after passing through an intermediate host, thought to be the pangolin.

Regardless of which animal it was, that one meal or medicine may end up costing humanity trillions of dollars and millions of lives.

What are the links between animals/livestock and pandemic diseases? How do modern farming practices assist in the evolution of new viruses?

There is a single species responsible for the COVID-19 pandemic—humans. Over the last few decades, hundreds of human pathogens have emerged at a rate unprecedented in human history. Emerged from where? Mostly from animals.

The AIDS virus is blamed on the butchering of primates in the bushmeat trade in Africa. We created mad cow disease when we turned cows into carnivores and cannibals. SARS and COVID-19 have been traced back to the exotic wild animal trade. Our last pandemic, swine flu in 2009, didn't arise from a wet market in Asia; it was largely made-in-the-USA on pig production operations.

Animal agribusiness has become a breeding ground for disease.

Today’s factory farming practices typically overcrowd thousands or even tens of thousands of animals in cramped, filthy, football-field-sized sheds. Animals are intensively confined and live beak-to-beak or snout-to-snout atop their own waste.

Animal agribusiness has become a breeding ground for disease. The sheer numbers of animals, the overcrowding, the lack of fresh air and sunlight, the stress crippling the animals’ immune systems, and the ammonia from the decomposing waste burning their lungs—put all these factors together and you have a Perfect Storm environment for the emergence and spread of new “superstrains” of influenza. Factory farms can be thought of as viral incubators for disease—a potential recipe for disaster.

What are the similarities and differences between the 1918 influenza pandemic and the current outbreak?

In 1918, it is estimated that half the world became infected. Unlike the regular seasonal flu, which tends to kill only the elderly and infirm, the flu virus of 1918 killed those in the prime of life. Ninety-nine percent of excess deaths were among people under age 65, and mortality peaked in the 22-34 age group.

The 1918 influenza pandemic killed more people in a single year than the bubonic plague—the “black death” in the Middle Ages—killed in a century.

The best estimate currently stands at 50 to 100-million people dead. The 1918 influenza pandemic killed more people in a single year than the bubonic plague—the “black death” in the Middle Ages—killed in a century. The 1918 virus also killed more people in 25 weeks than AIDS killed in 25 years.

The virus did stop, though. It ran out of human fuel—accessible people to infect. Those who lived through it were immune to reinfection, so many populations were, for the most part, either immune or dead.

Where did the 1918 virus come from? Humanity’s greatest killer appeared to come from avian influenza—bird flu. Evidence now suggests that all pandemic influenza viruses—in fact, all human and mammalian flu viruses in general—owe their origins to avian influenza.

Both the 1918 virus and the more recent H5N1 bird flu threat seem to trigger a “cytokine storm,” an overexuberant immune reaction to the virus. In laboratory cultures of human lung tissue, infection with the H5N1 virus led to the production of 10 times the level of cytokines induced by regular seasonal flu viruses. The chemical messengers trigger a massive inflammatory reaction in the lungs. A similar storm can rage in severe cases of COVID-19.

Cytokines are small secreted proteins released by cells that have a specific effect on the interactions and communications between cells.

While cytokines are vital to antiviral defense, the virus may trigger too much of a good thing. The flood of cytokines overstimulates immune components like natural killer cells, which go on a killing spree, causing so much collateral damage that the lungs start filling up with fluid.

“It actually turns your immune system on its head, and it causes that part to be the thing that kills you,” explains Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “All these cytokines get produced and [that] calls in every immune cell possible to attack yourself. It’s how people die so quickly. In 24 to 36 hours, their lungs just become bloody rags.”

Why are there more outbreaks of unknown or newly-discovered diseases now than there were 30 years ago?

In this new age of emerging diseases, there are now billions of feathered and curly-tailed test-tubes overcrowded and intensively confined in filthy factory farms for viruses to incubate and mutate within. Today’s animal agricultural practices have given viruses billions of more spins at pandemic roulette.

We may be one bushmeat meal away from the next HIV, one pangolin plate away from the next killer coronavirus, and one factory farm away from the next deadly flu.

Preventing coronavirus outbreaks

Coronaviruses are the second-most common cause of the common cold. Why is this outbreak so different?

There were more COVID-19 cases in the first month of reporting than SARS ever caused. Why? The primary reason revolves more around when it is contagious than how contagious it is.

The microbes most likely to cause pandemics have three characteristics:

  1. Novelty (without pre-existing immunity)
  2. Respiratory spread
  3. Transmission before the onset of symptoms.

One hundred percent of SARS patients developed a fever, as did 98 percent of MERS patients. However, as many as 36 percent—more than one in three—of COVID-19 patients do not present with fever at the onset of symptoms and, more seriously, may be infectious while completely symptom-free during the incubation period.

We can potentially spread COVID-19 before even knowing we have it, which is why isolation and social distancing measures may slow the spread of disease.

Unlike other deadly coronavirus outbreaks like SARS and MERS, COVID-19 appears to be like the flu in that people can be contagious before showing symptoms. We can potentially spread COVID-19 before even knowing we have it, even while we’re feeling completely fine, which is why isolation and social distancing measures may slow the spread of disease.

Has there ever been a successful coronavirus vaccine?

We haven’t yet created a successful vaccine for any coronaviruses. It’s humbling to realize that, historically, the average vaccine has taken more than a decade to develop, with an average failure rate of 94 percent.

Even though there are more than a hundred COVID-19 vaccine candidates now in the pipeline, I believe we should not expect to have a vaccine available to the general public until the second half of next year at the earliest.

Without a vaccine, herd immunity is only achieved the hard way—through mass infection.

Without a vaccine, herd immunity is only achieved the hard way—through mass infection. So, we must take all the measures we can to reduce our risk and, even more importantly, to prevent the emergence of the next pandemic virus in the first place.

What can we do as a society to minimize the risk of future deadly outbreaks?

How can we stop the emergence of pandemic viruses in the first place? Whenever possible, treat the cause.

The largest and oldest association of public health professionals in the world, the American Public Health Association, has called for a moratorium on factory farming for nearly two decades. Its journal published an editorial entitled “The Chickens Come Home to Roost” that went beyond calling for a de-intensification of the pork and poultry industries:

It is curious, therefore, given the pandemic threat, that changing the way humans treat animals, most basically ceasing to eat them, or at the very least, radically limiting the quantity of them that are eaten—is largely off the radar as a significant preventive measure. Such a change, if sufficiently adopted or imposed, could still reduce the chances of the much-feared influenza epidemic. It would be even more likely to prevent unknown future diseases that, in the absence of this change, may result from farming animals intensively and killing them for food. Yet humanity doesn’t even consider this option.

Factory farms are a public health menace. We don’t tend to shore up the levees until after disaster strikes, but the bottom line is that it’s not worth risking the lives of millions of people for the sake of cheaper chicken and pork.

A recent Neuroepidemiology editorial by the editor-in-chief entitled “What the COVID-19 Crisis Is Telling Humanity” concluded:

Intensive confinement of animals in factory farm operations should be discontinued worldwide for the sake of animals, humans, and the environment, and we should rapidly evolve to eating other forms of protein that are safer for humans, including plant-based meat alternatives and cultured meat (produced by culturing animal cells).

About the Author

Michael Greger, MD FACLM

A founding member and Fellow of the American College of Lifestyle Medicine, Michael Greger, MD FACLM, is a physician, New York Times bestselling author, and internationally recognized speaker on nutrition, food safety, and public health issues. He has lectured at the Conference on World Affairs, testified before Congress, and was invited as an expert witness in the defense of Oprah Winfrey in the infamous “meat defamation” trial. In 2017, Dr. Greger was honored with the ACLM Lifestyle Medicine Trailblazer Award. He is a graduate of Cornell University School of Agriculture and Tufts University School of Medicine. His latest book How Not to Die became an instant New York Times Best Seller. He has videos on more than 2,000 health topics freely available at NutritionFacts.org, with new videos and articles uploaded every day. All proceeds he receives from his books, DVDs, and speaking engagements is all donated to charity.