How the 1918 Flu Pandemic Affected Animal Health

The Hidden History of How a Human Health Crisis Shaped Veterinary Medicine

Hey Vortex Fam!

Blessing here, and today we’re dusting off the history books (and probably a few pathogens too, just kidding… I hope) to dive into an untold tale from the infamous 1918 Spanish Flu pandemic. You’ve probably heard how this deadly virus swept across the globe, infecting an estimated 500 million people - over a third of the world's population and claiming an estimated 17 - 50 million human lives.

But here’s the kicker: while humans were coughing up a storm and quarantining before it was trendy, what was happening to our furry, feathered, and hooved friends?

Today on Throwback Thursday, we’re getting into the nitty-gritty of how the 1918 flu rocked the animal kingdom because trust me, the four-legged weren’t just innocent bystanders.

Wait… Did Animals Even Get the Flu in 1918?

Short answer: Not the same strain that devastated humans.

Long answer? Buckle up.

The 1918 flu was an H1N1 influenza virus believed to have originated in birds (yes, avian), which mutated, and then made a jump to humans. That’s called a zoonotic spillover, by the way. We see it all the time (think swine flu, avian flu, SARS, etc.). It was spread through coughing, sneezing, contaminated surfaces, and close contact much like today’s seasonal flu but with a much higher mortality rate, particularly among young adults.

But in a plot twist straight out of a sci-fi drama, animals weren’t infected with the human strain, at least, not in large, documented numbers. There were a few curious cases in domestic animals, especially dogs and cats, showing signs of illness in flu-affected households, but evidence remains anecdotal. Virologists now believe the virus evolved via reassortment, a process where genetic material is swapped between different influenza viruses possibly in a bird or pig host allowing it to "learn" how to infect humans. Once airborne, it traveled the world via troop movements and trade routes at the end of World War I.

So, what does this have to do with animals?

Everything.

How Did It Affect Animal Health?

Horses Were the Silent Workhorses (Literally)

Black and white 1918 photo of a masked military veterinarian with a horse during the influenza pandemic, set on a brick street with masked pedestrians and historic buildings in the background.

Back in 1918, horses were still critical for transport, agriculture, and even war logistics. When the pandemic hit, and human labor plummeted due to illness and death. Horses had to shoulder the extra burden, they were essential workers, pulling carts, ambulances, farm equipment, transporting goods, and even helping dig graves. These animals faced longer hours, fewer breaks and minimal care.

I mean, if your job is literally pulling a plague cart? That’s a rough year.

Some veterinarians from that era noted a rise in lameness, exhaustion and neglect in working horses. These issues often manifested as increased cases of colic, hoof abscesses, and nutritional deficiencies, conditions largely attributed to overwork and underfeeding, likely stemming from the physical strain and inadequate care provided by handlers who were already overwhelmed by the demands of the time.

As one historian put it: "The horses kept society moving while people lay still."

Imagine being a horse vet in 1918. Overworked animals, sick owners, and zero digital X-rays or sedation. Count me out.

Swine Were About to Star in Their Own Pandemic

Here’s where it gets juicy.

In the early 1900s, pigs were already under the microscope because of respiratory illnesses sweeping through barns and farms. Although the 1918 human flu wasn't conclusively proven to infect pigs at that time, modern analysis of viral genomes has since shown swine and human strains shared a common ancestor.

That means pigs may have been unwitting players in the flu's evolutionary journey, even if they weren’t keeling over in 1918. By 1930, a flu virus isolated from a pig turned out to be almost identical to the 1918 strain in humans.

This early link to pigs laid the groundwork for how we later understood zoonotic flu and how we manage modern outbreaks like H1N1 “swine flu” in 2009.

Oink if that freaks you out.

Dogs and Cats: Anecdotal But Not Immune

There are sparse records of domestic pets getting sick during the 1918 pandemic, but veterinarians noted that some cats and dogs in flu-affected homes developed respiratory signs, including coughing and lethargy. However, there’s no evidence they transmitted the virus back to humans.

It’s still debated whether these animals were truly infected or just coincidentally ill.

What Could Vets Do in 1918?

Let’s be honest: vets back then didn’t have diagnostic labs, antivirals, or even a solid grasp of virology. The first influenza virus wouldn’t be isolated until 1931. So how did vets cope?

Symptomatic care: Hydration, rest and feeding.
Isolation of sick animals to prevent suspected transmission.
Manual labor: Vets had to care for large numbers of overworked livestock with little support.

Despite their limitations, vets in 1918 served as early champions of disease surveillance and animal welfare, especially in agricultural settings.

What Can Pet Parents Do Today?

While the 1918 flu didn’t significantly impact pets, times have changed. Modern flu strains and viruses like COVID-19 have shown us that animals can be affected, especially in cases of zoonotic (animal-to-human) or reverse zoonotic (human-to-animal) transmission. So, if there’s a human flu outbreak or a novel respiratory virus making the rounds, here’s how pet parents can help protect their furry family members:

Watch for Symptoms in Pets:

Coughing, sneezing or nasal discharge
Lethargy or appetite loss
Fever (rare, but possible)

Practice Good Hygiene:

Wash hands before and after handling pets.
Avoid kissing, cuddling or sharing food with your pets if you're sick.

Isolate When Necessary:

If you’re ill with a virus that could potentially spread to animals, limit close contact with your pet.
If possible, have a healthy family member take over pet care duties until you recover.

By taking these simple steps, you’re not just protecting your pet, you’re helping break the chain of transmission in both directions.

What Can Vets Do?

Veterinarians today are far better equipped than their 1918 counterparts. Here’s how we handle suspected viral infections in animals during a flu or pandemic situation:

Diagnosis:

Nasal or throat swabs (PCR testing)
Chest X-rays if pneumonia is suspected
Blood work to check inflammation or dehydration

Treatment:

Supportive care: Fluids, rest, nutrition
Oxygen therapy in severe respiratory cases
Antivirals (rarely used and off-label)

Prevention:

Flu vaccines are available for dogs, horses, and pigs, but not for cats (yet).
Regular veterinary wellness exams.
Biosecurity practices in farms and shelters.

Zoonotic and Reverse Zoonotic Implications

The 1918 flu taught us a vital lesson: human and animal health are intertwined.

Zoonosis:

This occurs when diseases jump from animals to humans; like avian flu, swine flu, or the original spillover suspected in the 1918 pandemic.

Reverse Zoonosis:

This happens when diseases jump from humans to animals something we saw with COVID-19 in pets, mink farms, and even zoo tigers.

This dual threat highlights the essential role veterinarians play in pandemic prevention, disease surveillance, and public health education. In a world where viruses don’t respect species boundaries, vets aren’t just animal doctors; they’re frontline defenders of One Health.

Prognosis: Then vs. Now

In 1918:

Animals weren’t the virus’s primary target, but many suffered indirectly.

Working animals, especially horses, faced exhaustion, malnutrition, and neglect as their human caretakers struggled with illness and societal collapse. The limited veterinary infrastructure of the time made recovery difficult, if not impossible.

In 2025:

Today, flu in animals is typically mild and treatable—especially with early detection.

Thanks to modern veterinary care, diagnostics, and supportive treatment, the prognosis is excellent for most pets and livestock affected by influenza or similar
respiratory illnesses.

Split image showing evolution of veterinary care: a 1918 vet writing notes beside a horse versus a modern vet using a tablet while treating a dog and cat in a contemporary clinic

But one thing hasn’t changed:

vigilance is key, especially in multi-species households, farms or during outbreaks of new or emerging respiratory viruses. Early action can make all the difference.

A Century Later… We're Still Learning

Fast forward to my veterinary training (and late-night pandemic rabbit holes), I remember reading about the 1918 flu and thinking: “Thank God we’ve come so far.”

But then COVID-19 hit, and suddenly it was 1918 all over again, except this time with WiFi and sourdough starters. And yes, this time animals did get infected.

The 1918 flu may not have infected animals on a massive scale, but it set the stage for modern zoonoses. It taught us to keep an eye on our species-jumping viruses and reminded us that human and animal health are deeply connected, something we now call One Health.

Personal Vortex

Okay, real talk?

As a vet, I often reflect on the resilience of animals and people during historical health crises. In 1918, there was no WHO, no mass vaccination rollout, and minimal understanding of viruses.

Yet, vets still showed up. They took care of horses, cows, pigs, and pets. They cleaned up, stitched up, and kept calm. Even in the shadows of a global catastrophe.

Sometimes, I feel like I’m channeling those early 20th-century vets, just trying to make a difference for one more patient.

And honestly? I wouldn’t have it any other way.

Throwback Wrap-Up

Here’s what we learned from our dusty, flu-filled time machine:
The 1918 flu didn’t decimate animals, but it affected them indirectly; through overwork, neglect, and systemic chaos.
Horses bore a heavy burden during the pandemic while humans struggled to stay alive.
Swine flu’s origins may trace back to the same viral pool that created the 1918 pandemic.
Vets played a crucial role then and still do now, in bridging the gap between human and animal health.

Over to You!

Do you have any animal stories passed down from older generations during times of illness or crisis? Maybe your great-granny’s cow survived the flu and lived to be 20? Drop it in the comments. I love sharing real-life vet vortexes from across the ages.

Until next time, stay vortexy, stay curious, stay kind, and for the love of science, wash your hands (again).

Check out previous post - Joint Health in Dogs