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New book by �鶹��Ѱ�����Boulder historian Thomas G. Andrews documents the forgotten epidemic that hobbled America and had wide-ranging effects on society

When Americans picture the 1870s, they likely imagine an age defined by railroads, steamships and rapid industrialization. Yet, �鶹��Ѱ����� historianThomas G. Andrews argues those familiar images obscure a more important reality: 19th century North America still ran on horsepower.

“Horses were doing essentially all of the things that internal combustion engines do for us today,” says Andrews, who serves as the director of the Center of the American West and whose research focuses on the environmental and social history of the American West. “As someone recently said to me, horses were the forklifts of the 19th century and that’s exactly right.”

�鶹��Ѱ�����Boulder history Professor Thomas G. Andrews, whose research focuses on the environmental and social history of the American West, is the author of the new book, The Great Horse Flu: A Forgotten Contagion and the Fate of Reconstruction America, which documents how America’s horse-powered economy was paralyzed by horse influenza.��

That dependence upon horses, donkeys and mules explains why a largely forgotten outbreak, which Andrews calls the Great Horse Flu, proved so devastating at the time. The disease, which first appeared in 1872 and did not let up until late 1873, infected as much as 90% of North America’s equine population, hobbling transportation systems, slowing commerce, complicating public safety efforts and contributing to an economic depression in the United States.

The disease and its consequences are the subject of Andrew’s new book, , which places the outbreak at the center of a transformative moment in North American history.

Origin of the outbreak

Andrews acknowledges there is a lot historians and scientists still don’t know about the Great Horse Flu, in part because no physical samples of the virus exist today. However, he says his research does point to the origins of flu, which began in an inland farming area outside of Toronto, Canada.

Why there?

While it’s impossible to say with 100% certainty, Andrews speculates that it had to do with the confluence of settlers introducing improved breeds of livestock from different regions, which brought new influenza variants with them, and the area’s extensive wetlands near Lake Ontario that supported vibrant populations of wild waterfowl, which are known carriers of influenza diversity.

“You had humans, domestic animals and wild birds all interacting in one environment. In retrospect, it’s easy to see how an influenza variant could emerge there,” he says. “What’s much harder to explain is why it happened there instead of somewhere else with similar conditions.”

Because the outbreak occurred in a rural area not near a major sea or lake port, and because there are no reports of major outbreaks from elsewhere in the world during the same period, Andrews says it seems clear that “rather than being imported, this seems to be something that evolved in that place and time.”

While the particular circumstances of the flu’s origins remain a mystery, Andrews says the infection rates in equines strongly suggest this was a novel form of virus.

“Any influenza strain that reaches those kinds of infection rates is either striking a population that has never encountered that type of virus before or one that has never seen that particular variant,” he explains. “Once this novel variant emerged, it easily bypassed the immune defenses horses would normally have.”

Virus spreads across the U.S.

Once the horse flu crossed the border from southern Canada into the United States, it quickly spread to major East Coast population centers such as New York, Philadelphia, Baltimore and Boston and then fanned out to the south and west.

“This outbreak spread so quickly because it was perfectly suited to exploit the economies and societies of North America,” Andrews explains. “Virtually everyone depended on horses, donkeys and mules for transportation. Horses were everywhere. They worked constantly, came into contact with other horses, and often did so in confined spaces like stables, city streets and farmyards.

“Sometimes, the virus traveled with horses being moved by rail or steamship, creating what looked like leapfrog outbreaks,” he adds. “In other cases, there were apparent super-spreader events, such as a traveling circus troupe that crossed from Ontario into New York and was blamed for introducing the disease into several communities.”

Once horse influenza reached a community, it tended to spread like wildfire.

“In places where we have detailed records, the outbreak generally infected at least of 90 percent of horses, donkeys and mules,” Andrews says. “There were reports from Brooklyn claiming that virtually every horse in the city had contracted the disease. Similar infection rates appear in rural areas.”

Andrews estimates the overall mortality rate was somewhere between 1% and 4%, amounting to anywhere between 112,500 and 540,000 horses, in addition to tens or even hundreds of thousands of mules and donkeys. Donkeys seem to have been affected most severely, although the reasons remain unclear, he adds.

“The vast majority of animals recovered,” Andrews says. “However, there is clear evidence of what I would call ‘long flu.’ Some horses remained sick for months. Some never regained their previous strength. There are scattered reports of horses dying more than a year after their initial infection. Those patterns look remarkably similar to what we now see in post-viral syndromes, such as long-COVID.”

Impacts on everyday life

Horses and other equines might most commonly be associated with agriculture and ranching in the 1870s, but in truth they fulfilled many other vital functions, Andrews says. As a result, horse flu impacted most areas of transportation, commerce and industry.

“The outbreak was so disruptive because it was highly infectious, horses were essential to so many aspects of everyday life and people responded by removing their sick animals from service,” Andrews says.

They were used extensively on farms to work fields and transport crops. Even on farms where horses did not get sick, Andrews says farmers were often reluctant to transport their produce into cities for risk of exposing their horses to the contagion, slowing commerce.

In cities, streetcar companies reduced transportation services. Meanwhile, commerce slowed to a crawl, as horses were used to haul freight and move canal boats. Horses were also used heavily for coal mining, logging operations and some aspects of manufacturing.

“While cotton presses were often steam-powered, horses were essential for moving materials within warehouses and industrial facilities,” Andrews says. The combined effect of so many horses out of commission, he says, was that “production slowed, goods moved more slowly and trade networks became constrained.”

Typically, the onset of horse flu reduced conditions in impacted areas to a crawl for a week or two, but Andrews says it often took several more weeks for things to begin to return to normal.

Flu and a great fire��

The Great Horse Flu also played a role in the disastrous of November 1872, which destroyed 776 buildings across 65 acres and caused estimated property damage of between $66 million and $73 million.

For reasons that remain unclear, the Great Horse Flu originated outside of Toronto, Canada, and then quickly spread to major U.S. East Coast population centers before fanning out to the south and west. According to Andrews, horse flu contributed to the Great Boston Fire of November 1872 and it played a part in the Panic of 1873, which resulted in a years-long depression.

“Horse flu was an important contributor to the fire, but the relationship is more complicated than people often assume,” Andrews says. “The simple version of the story is that horses pulled fire engines, the horses got sick and therefore the fire spread. There’s some truth to that, but it’s not the entire explanation.”

It was precisely because of horse flu that the transport of most commercial goods had ground to a halt in the city, causing highly flammable materials such as cotton, leather, oil and paper to accumulate in warehouses in the downtown area, Andrews says. He says the Boston Fire Department recognized the problem at the time and had developed a contingency plan, which involved having dozens of volunteers pull fire engines using ropes.

“Over short distances, humans could move the equipment almost as quickly as horses. The problem arose over longer distances,” Andrews says. “As fire alarms increased and fire engines had to travel from farther away, people simply could not match the stamina of horses.”

The horse flu outbreak also made it difficult to deliver coal needed to power the engines and prevented many residents from saving their property because there were too few healthy horses available to move their belongings, he adds. What’s more, he says downtown Boston at the time did not have enough modern fire hydrants or upgraded water pipes.

“The horse flu absolutely contributed to the disaster, but it interacted with many other factors,” Andrews says.

He adds that horse flu, combined with the Great Boston Fire and the Great Panic of 1873, led to a years-long economic depression.

“When the horses became sick, everything became slower, more expensive and less efficient. Those effects spread throughout the economy,” he says. “The Panic of 1873 was the trigger (for the depression), but the horse flu outbreak imposed economic costs for roughly a year. When you add together its effects across different regions and industries, the consequences became significant.”

Lessons learned and forgotten

Andrews says that the Great Horse Flu ultimately seems to have petered out after 1873 as it moved farther south, into Mexico, Cuba and Central America. Still, in the years immediately following, Americans continued to reflect on the impact the contagion had on the country, often relating it to timely breakdowns in transportation, commerce and industry, he says.

“Unlike the 1918 flu pandemic, which many historians argue faded quickly from public memory, the Great Horse Flu continued appearing in public discussion into the 20th century,” Andrews says. “I think that’s because the experience was so unusual; it turned life upside down.”

Still, in time, memories of the contagion faded.

Andrews believes some of that is due to the way history is taught. He notes the late 19th century is usually remembered as the age of railroads, factories and steam power. Horses receive comparatively little attention despite remaining essential to daily life. He says another factor is that relatively few people realize horses can contract influenza.

“Finally, the outbreak was diffuse. It was disruptive, but it didn’t have the catastrophic mortality we often associate with events that become central to collective memory,” Andrews says. “The goal of the book is to show that this seemingly forgotten event actually had profound consequences.”

Why it matters today

For Andrews, the story of the Great Horse Flu is more than an exercise in historical recovery. It’s a reminder of how dependent societies can become on a single piece of infrastructure—and how vulnerable they can become when something goes wrong.

Researching his book during and after the COVID-19 pandemic reinforced that lesson.

“It (horse flu) reminds us that influenza remains a remarkably adaptable and powerful disease,” Andrews says. “We need to recognize that diseases moving between humans and animals will continue to pose serious challenges. The history of disease isn’t simply a story of scientific triumph. It’s also a story of ongoing adaption and vulnerability.”

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