The history of Theiler’s disease and the search for its aetiology.

This research article explores the history and causes of Theiler’s disease, an often fatal viral infection in horses often associated with receiving biologics of equine-origin, comparing historical epidemic data to recent studies, and suggesting equine parvovirus-hepatitis as the likely cause.

Overview of Theiler’s Disease

• The article starts by discussing the nature of Theiler’s Disease, also known as serum hepatitis. This condition tends to occur either in outbreaks or as individual cases of acute hepatitis.
• The disease is often associated with the administration of equine-origin biologics, such as vaccines and antitoxins, roughly 4-10 weeks before the onset of clinical symptoms.
• However, cases have also been described where Theiler’s disease has developed without any prior administration of blood products.
• The disease affects only adult horses and has a low morbidity but high mortality. the course of the disease is typically short, with horses either dying or recovering completely within a few days.

Exploration of Disease Pathology

• Pathologically, the disease primarily causes centrilobular hepatocyte necrosis (cell death in the liver) with mononuclear (single nucleus) cell infiltration in the less affected periportal regions of the liver.
• There are also subclinical cases of Theiler’s disease, in which the horse is infected with the virus but does not exhibit symptoms.
• Based on its epidemiology and pathology, Theiler’s Disease has long been suspected to be caused by a virus similar to the human’s hepatitis B.

Historical and Recent Findings of Theiler’s Disease

• The paper reviews both historical and recent findings on Theiler’s Disease, covering reported epidemics in the early 20th century.
• The early outbreaks of the disease are compared to outbreaks of serum hepatitis in humans after yellow fever virus vaccinations in the 1930s and 1940s, suggesting similarities in their causes and presentations.
• Recent metagenomics-based studies, which investigate the genetic material of all microorganisms in a particular sample, are discussed in relation to determining the cause of Theiler’s Disease.

Equine Parvovirus-Hepatitis as a Likely Cause

• The paper concludes with both clinical and experimental findings suggesting that Equine Parvovirus-Hepatitis (EqPV-H) is the likely cause of Theiler’s Disease.
• The EqPV-H is a fairly newly discovered virus and the statement is supported by the similarities in the presentation of illnesses caused by other known parvoviruses.
• Therefore, this paper provides significant support for this virus being the culprit behind Theiler’s Disease that has puzzled scientists for over a century.