What Have Horses Got to Do With It?

In the course of doing the research for my next Jenny Black Wolf – Curran TaZarin book, I’ve been reading a lot of books about virology, viral ecology, microbiology, and infectious diseases. That inevitably brought me to the poster child for infectious diseases, the 1918 influenza pandemic. Here’s something I didn’t know before that caught my attention, so I kept looking into it.

First, people aren’t the only ones who get the flu. Other animals can get it, too, including horses. During World War I, cavalry units were still being used. Also, most transport, both military and civilian, was horse-drawn. Field artillery was also horse-drawn.

Cavalry Unit At Fort Riley, Kansas, circa 1918

Equine influenza was a major problem for the military throughout the war, even before the pandemic began, killing or disabling many previously healthy horses. However, outside the army, veterinarians weren’t interested in the pandemic, and military veterinarians didn’t generally connect the horse version of the disease to influenza in humans—not even veterinarians who specialized in the parallels between veterinary medicine and human medicine. Further, most medical doctors weren’t interested in a possible connection between horse and human influenza, either.

Horse-Drawn Field Artillery

During the war, the Netherlands was neutral, but its army was mobilized. In the years prior to the war, Emile Bemelmans, one of the Netherlands top military horse veterinarians was actively involved in research aimed at discovering the cause of equine influenza and finding a treatment for it. In 1919, after the terrible autumn 1918 wave of the pandemic, Bemelmans wrote and published a paper in a Dutch medical journal, contending that human and equine influenza are identical diseases and noting their similarities and common features. He also presented his theory at a meeting of the Amsterdam Society for the Promotion of Physics, Medicine, and Surgery.

Bemelmans’ theory as presented in the medical journal was reviewed in an important veterinary journal but there were no further references to Bemelmans’s ideas in the journal, and no other publications about influenza in animals during the 1918–1919 influenza pandemic.

WWI Army Supply Wagons

In his paper, Bemelmans said he was unsure about the exact causes of the disease because he was unable to artificially infect horses with human influenza, or horses reciprocally with influenza. (Medical doctors researching the pandemic influenza in humans were having the same problem in trying to cause disease in lab animals.) Bemelmans thought that equine influenza and human endemic influenza (the mild seasonal variety) were the same, but he was uncertain about the relationship between endemic and pandemic influenza, again like many other influenza researchers of the period.

In an official report written by noted military physician, major general A.A.J. Quanjer, Quanjer referred to Bemelmans’ medical journal article in a section on etiology and related it to earlier observations of similarities between human and animal influenza in a medical textbook by Berlin medical professor August Hirsch (1817–1894). Hirsch had pointed out simultaneous historical outbreaks of influenza among people, horses, dogs, cats, and other animals and the relationship between human influenza epidemics and influenza epizootics in animals, remarking that there were so many such observations in history that the idea of a common etiology and possibly even a common pathology between those epidemics and epizootics seemed reasonable.

Quanjer also discussed a letter he had received from an army physician during 1918–1919 pandemic who noted that all of the influenza-infected soldiers from the artillery battery at his base in Ede had stayed in a hayloft above a stable housing army horses. The horses from this battery were also suffering from an influenza-epidemic.

Many similar observations of a relationship between human and horse influenza came from other countries involved in the war and also linked back to Bemelmans’ theory.

So when and where did the pandemic begin? There are lots of theories, but here’s the one I’ve read the most times.

Horse Corral at Fort Riley, Kansas

In 1918, Fort Riley, Kansas was the focal point of US Cavalry training — everything from horsemanship to tactics to veterinary medicine to the training of farriers, saddlers and harness makers. Attached to Fort Riley there was a nearby infantry training camp named Camp Funston. Between 35-50,000 soldiers and thousands of horses were there at any one time, then shipped out to other camps and eventually sent overseas.

The fort’s horses produced hundreds of tons of manure every week and the army’s way of dealing with it was to burn it. On March 9, 1918, while the daily manure-burning was going on, a huge dust storm was barreling across the prairie headed straight toward Fort Riley.

When the dust storm hit the fort, it produced a miasma of dust mixed with the ash from the burning manure, creating a stinging, stinking yellow haze that turned the Kansas day dark as night. It was so bad they had to halt trains on the tracks. When it was over, Fort Riley was covered in soot, ash and dust. No one seemed to consider what might have been in the dust and ash and the men who were assigned to clean up the mess didn’t wear masks.

Two days later, more than 100 men had reported sick to the infirmary at Camp Funston as the flu began to ravage the camp and it only got worse from there. During this outbreak, soldiers from Camp Funston and horses and personnel from Fort Riley were sent to other camps all over the country and eventually on to ships headed for France. For political reasons, quarantining at these two camps and the many other training camps where flu became rampant was never instituted, despite pleas from camp medical officers.

Infirmary at Camp Funston

By April the flu started to hit soldiers fighting in France.

The 1918 influenza pandemic caused an estimated 50 million to 100 million deaths worldwide. The virus that caused it probably came from North American domestic and wild birds. Fort Riley is located on the Kaw (Kansas) River which is on the Central Flyway and frequented by migratory birds. One source I read said that many other animal species also had influenza in 1918. In the fall of 1918, reports came from northern Canada that influenza was decimating big game. At Yellowstone National Park the bison, elk, and other animals were getting sick. Much later, a definitive link was made showing a common connection to horses, although Fort Riley was probably not the lone source of the virus.

Farriers at Fort Riley

Bemelmans’ theory was important for human influenza research and helped shape the development of ideas about a shared etiological relation between human and horse influenza. The knowledge developed by military veterinarians helped clarify the many historical reports on horses with influenza that microbiologists have now connected to the ecology and evolution of influenza. Based on these reports, biologists speculate that horses throughout history have been a reservoir for influenza virus maintenance and evolution as pigs are now in the modern era.