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Animals of the Great War, Part 3: The Secret War on Horses


2014 marks the hundredth anniversary of the beginning of World War I.

In addition to humans, the war involved millions of animals - from horses to pigeons to slugs! 

In this special year, our Laura Brown, Auxiliary Veterinary Nurse, writes a series of articles remembering animal helpers, heroes and victims of the war.


The role of horses in World War I is well known. Eight million horses died in the war, and many others were wounded or traumatised. Horses faced all the same dangers as their riders: gunfire, bombs, gas, hunger, cold, and disease spread by unsanitary conditions. But horses were also the focus of a little-known campaign of biological warfare.

After the outbreak of war, it quickly became apparent that the Allies did not have enough horses to meet their needs. The United States, although still officially neutral, began supplying horses to Britain and France. Nearly 500,000  were sent across the Atlantic over the course of the war, including not just cavalry horses but farm animals and feral mustangs.

A horse being transported to war. Public domain image from the Australian War Memorial (

A horse being transported to war. Public domain image from the Australian War Memorial (

This provided a perfect opportunity for Dr Anton Dilger, an American citizen of German heritage. Having trained as a physician in Heidelberg, Dr Dilger was practicing in Washington. D.C. -- and he was also one of many German secret agents working within the U.S. to sabotage any aid given to the Allies. Between spring 1915 and autumn 1916, Dr Dilger created bacterial cultures in his basement laboratory that were used to infect more than 3500 horses with glanders and anthrax.

Anthrax will be familiar to many due to its use in terrorist attacks in the U.S. in 2001. Animals are infected when they breathe in bacterial spores or eat food with spores on it. Within two weeks, a horse with anthrax will develop a fever, colic, bloody diarrhoea and swellings throughout its body. Without treatment, death almost always results in two or three days.

Burying horses killed in battle. Copyright-free image from Library of Congress (

Glanders is less well known today; no cases have been reported in the UK since 1928 (although it remains a problem in many other parts of the world). But it is no less distressing. Animals catch it by consuming food or water contaminated with bacteria. Some horses suffer from an acute form, with high fever and trouble breathing. Unless they are treated, they usually die within a few days. But it is also possible for horses to get a chronic form of glanders, in which nodules develop in the mucous membranes or lymph nodes and the horse becomes very weak. Horses with this form of glanders may live for years, and they will be contagious the whole time.

Dr Dilger’s purpose in spreading these diseases was to make horses unfit for service. The Kaiser had specifically forbidden the use of biological weapons against humans. Nonetheless, Dr Dilger’s programme could still have had this effect, because both anthrax and glanders can spread from horses to people.

Fortunately, the German biological warfare programme was not very successful. In his book Spies of the Kaiser, which tells Dr Dilger’s story in detail, historian Thomas Boghardt estimates that only five cases of anthrax in the British Isles can be linked to German sabotage. It may be that the cultures of bacteria were too weak to cause widespread infection. At least two German agents were caught trying to infect horses in the UK, but their efforts also seem to have been unsuccessful.

Biological weapons were banned by international treaty in 1975, although there are still worries about their use by terrorists or rogue states. Anthrax and glanders remain dangerous, but can now be treated with antibiotics; there are also anthrax vaccines for both animals and humans. Scientists have become very conscious of the risk of diseases spreading from one species to another, and veterinarians and physicians increasingly work together to protect the health of both humans and animals.

And what became of Dr Dilger? Perhaps fittingly, he died in the worldwide influenza pandemic of 1918.


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