He described in 1919 what is now known as Theiler's disease (acute serum hepatitis, postvaccination hepatitis or idiopathic acute hepatic disease) - one of the most common causes of acute hepatitis in horses - when he observed the symptoms of liver disease in animals vaccinated against African horse sickness with a combination of live virus and equine antiserum.[2] This disease is now known to be caused by a parvovirus.[3]