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10 of the Worst Pandemics in History: Is COVID the Worst?

February 15, 2022

It’s difficult to know exactly how many pandemics have taken place throughout human history since they have been happening for as long as humans have existed as a species.

How Many Pandemics Have There Been? 

It’s difficult to know exactly how many pandemics have taken place throughout human history since they have been happening for as long as humans have existed as a species. In 2015, a team of researchers discovered a house in China that dates from 3,000 BC filled with the prehistoric remains of dozens of humans from all age groups, possibly killed by a pandemic. For much of human history, such mass death could easily have spelled doom for entire communities. Thankfully, advances in epidemiology and medicine mean that pandemics can often be better controlled as long as proper precautions are taken. Yet despite these advances, we are placing ourselves at risk due to the ways that farmed animals are housed and treated and slaughterhouses are run. Close proximity to unhealthy animals increases the likelihood of spillover diseases. And deforestation globally, primarily driven by animal agriculture,  is another source of spillover diseases from nonhuman animals to humans. 

Is COVID the Worst Pandemic in History? 

At the time of writing, COVID-19 has killed over 5.5 million people worldwide, including nearly a million in the US. This number is still increasing as the pandemic rages on. Though the number of lives lost is staggering, there have been pandemics with even higher death tolls including the HIV/AIDS pandemic and the Black Death. Thankfully governments and individuals all over the world took action by implementing and abiding by stay-at-home and other public health  orders to prevent the COVID-19 death toll from rising. 

What Was the Biggest Pandemic before COVID-19? 

There have been several pandemics that rivaled COVID-19 for size. The measures taken to control the spread and severity of COVID-19 have prevented it from becoming as destructive as pandemics could be before modern advances in epidemiology and disease treatment. For example, though many lives have sadly been lost to COVID-19, and individuals continue to die the world over, the confirmed death toll is just a fraction of that of the Spanish Flu, which impacted one-fifth of the world’s population. In just six years the Black Death—a disease originally spread by fleas carried by rats—killed between 30 and 60 percent of the population of medieval Europe. 

10 of the Worst Pandemics in History

Black Death

The origin of the Black Death, a bubonic plague pandemic, has long been debated, but the predominant modern theory is that the disease originated from the fleas that live on rats. These rats (and fleas) stole away on ships and spread the disease from Asia to Europe and then from city to city. The disease was especially deadly because in addition to being spread this way, it became airborne and began infecting its victims even more efficiently. Those that contracted the Black Death endured horrendous pain and suffering. Their bodies became covered in boils which were accompanied by vomiting, diarrhea, fever, and chills. Though modern medicine has created antibiotics and treatments for bubonic plague, it has never truly been eradicated, with between 1,000 and 3,000 cases reported yearly. 

Spanish Flu

The Spanish Flu infected an estimated 500 million people around the world, killing between 20 and 50 million of them. Like COVID-19, the Spanish Flu spread worldwide and resulted in the shuttering of a number of establishments such as theaters and schools. The pandemic occurred in two waves. The first was mild and most patients recovered in a few days. The second, however, was deadly, with victims dying in mere hours or days following the development of symptoms. In 1918 alone, the average life expectancy in the United States fell by 12 years. The 1918 flu is believed to have spilled over from bird populations.

Plague of Justinian

Another pandemic outbreak of bubonic plague, the Plague of Justinian, was also spread by fleas and rats aboard trade ships along trade routes of the Byzantine Empire. The rats were especially interested in the large grain stores that were shipped from North Africa to Constantinople, and reached the rest of the empire along both shipping and land routes. The plague resulted in a weakening of the once-mighty empire. The military struggled to recruit and maintain soldiers due to the rapid spread of disease and death.

HIV/AIDS Global Epidemic

The HIV/AIDS Global Pandemic persists to the present. In 2020, 37.7 million people globally had HIV, 1.5 million people acquired the disease, and it caused the deaths of 680,000 people. AIDS-related deaths have steadily dropped from the 1.9 million that died from the disease in 2005. 

COVID-19 Pandemic

The ongoing COVID-19 pandemic is a perfect example of the ties between human and animal health. It is theorized that the disease spread directly from animals to people, potentially at an illegal wildlife market at which animals are often housed in unsanitary conditions. Throughout the pandemic, there have been numerous occurrences of animals contracting COVID-19, with the chance of it being spread back to people. Concern over this resulted in the mass slaughter of minks in Denmark, who were being raised on factory farms for their fur.  

Third Plague Pandemic

While the Third Plague Pandemic touched countries all over the world in the middle of the 19th century, the largest impact was felt in China, where tens of thousands fell victim to the plague. From there it spread to the United States, Europe, and South and Central America reflecting the world’s growing interconnectedness. However, science and medicine were also improving, allowing for the development of treatments that have helped to prevent future pandemics of bubonic plague. 

Cocoliztli Epidemic of 1545–1548

The Cocoliztli Epidemic killed an estimated 45 percent of the entire native population of Mexico (then New Spain). The symptoms were like nothing doctors had seen at the time and included jaundice and blood spilling from the nose and ears followed by death just a few days later. An analysis done in 2018 suggests that the disease may have been salmonella introduced to native populations by colonizers and the animals that they brought with them. Despite the new evidence pointing to salmonella, researchers are hesitant to say that is what killed so many natives, and also suggest that the mass death may have been due to a number of diseases combining to cause the epidemic.

Antonine Plague

The Antonine Plague has been recognized by historians as one of the factors that contributed to the decline and eventual end of the Roman Empire. The plague impacted every facet of society—from religion to military strength and the economy.

1520 Mexico Smallpox Epidemic

Disease decimated indigenous populations in Mexico when Spanish colonizers arrived. In 1520, smallpox killed 40 percent of the population of Tenochtitlan, the center of the Aztec Empire and home to 200,000 people. Without the introduction of smallpox, the conquest of the great island city would have been impossible.

1918–1922 Russian Typhus Epidemic 

Between 1918 and 1922, typhus swept through Serbia and Russia resulting in 30 million cases and 3 million deaths. The spread of the disease weakened the Russian military and extended World War I, as Germany withdrew troops from the Eastern Front and strengthened its Western Front. 

What Role Can Animal Advocates Play in Preventing Pandemics? 

As animal advocates, we should recognize and keep in mind the ties between animal welfare, animal agriculture in general, and public health. Below are just some of the issues related to animals that can have an impact on human health. 

Factory Farming

Animals on factory farms are kept in conditions that create the perfect breeding ground for the spread of disease. Workers at one Russian chicken farm were perplexed when tens of thousands of birds fell ill and died in December 2020. Following testing, it was revealed that the birds had died of a new strain of avian flu. To make matters worse, when the workers were tested for the disease, seven were found to have a mild case, the first time this strain was known to have made the jump from chickens to humans. Despite the cause for concern, little was done about the spread due to the ongoing COVID-19 pandemic.

On factory farms, thousands of animals are housed in cramped conditions, often standing in their own waste, and fed a steady supply of antibiotics. Mass-breeding means these animal are nearly genetically identical. These conditions are ripe for the start of yet another pandemic.

Fur Farming

Like animals farmed for food, on fur farms animals are kept in cramped conditions with little concern for cleanliness. These conditions are especially risky on mink farms. Over 400 mink farms in the United States and Europe have been impacted by COVID-19, resulting in the culling of over 20 million minks. The concern surrounding minks specifically is due to the ability of COVID-19 to jump back and forth from humans to minks with the possibility of mutation prior to being transmitted back to humans. 

Wildlife Trade 

During COVID-19 there have been continued efforts to stop the illegal wildlife trade. The illegal transport and sale of wildlife may have contributed to the present pandemic, with its unsanitary conditions and close contact between humans and a variety of animal species. To help ensure that this trade shuts down permanently, we can each do our part by eliminating the demand for these exotic animal species.

Deforestation and Destruction of Habitat

The primary cause of deforestation in the most diverse ecosystems on the planet, like the Amazon rainforest, is animal agriculture—both to grow soy and corn to feed animals on factory farms in the United States, China, and other countries, and to graze cows during the first part of their lives as factory farmed animals. Loss of habitat for the millions of wild animals in these ecosystems causes massive biodiversity loss and forces multiple species to live closer together and fight for limited resources, puttings them into closer proximity with humans. Several recent high mortality human diseases resulted from spillover from wild animals due to humans being in close proximity with them.


Animal health and welfare are intrinsically tied to public health and the prevention of future pandemics. Throughout history, animals have had a hand in spreading disease whether they be fleas, rats, farmed animals, or wildlife. To prevent future pandemics we must take the crucial steps of increasing animal welfare in every area, ending the confinement of large numbers of animals, and preserving habitat for wild animals wherever possible. We can help by choosing to consume more plant-based foods and reducing our meat consumption to protect not only the animals but also ourselves and those we love.