Equis ISSN 2398-2977

Liver: hepatitis - acute (Theiler's Disease)

Synonym(s): Theiler's disease


  • Acute fulminant hepatitis in adult horses with no proven toxic cause is known by both Theiler's disease and/or serum hepatitis when a blood product has been administered 4-10 weeks prior to the onset of clinical disease.
  • There appears to be two distinct historical scenarios (prior blood product administration or not) with identical clinical, laboratory and pathological findings.



  • A pegivirus was found in association of an outbreak of Theiler's disease that followed equine plasma administration. This is the presumed cause of Theiler's disease in adult horses that have received equine origin biologic administration 4-10 weeks earlier.
  • Further research is needed to confirm this and to determine if there might also be an association between the virus and the non-biologic associated cases of Theiler's disease.
  • Unknown.
  • Possibly - virus, mycotoxins   Mycotoxicosis  .


  • Some cases associated with administration of serum/biologic products.
  • If the recently discoveredpegivirus or Theiler's disease-associated virus (TDAV)   Theiler's disease-associated virus   is further confirmed to be the cause of Theiler's disease/serum hepatitis, it would be reasonable to propose the following pathophysiology:
    • Following infection with TDAV, the virus both circulates in the serum and has trophism for the liver.
    • In an unknown percentage of horses, antigen-antibody reactions may attempt to clear the virus causing an immune-related apoptosis and necrosis of hepatocytes.
    • If sufficient hepatocytes are lost such that more than 60% of functional mass is destroyed, clinical signs of acute hepatic failure would be expected.
    • Some infected horses may have biochemical evidence of liver disease but not have sufficient damage to cause liver failure. Other horses with TDAV infection may not have any biochemical or clinical effects from the virus and some may become healthy persistent carriers.
    • Horses with acute hepatitis/Theiler's disease that have no recent history of equine origin blood product inoculation may have different causes for the acute hepatitis or transmission of the presumed infection agent, TDAV, may be by means other than planned blood product administration. Interestingly, the non-biologic origin cases of Theiler's disease generally occur in late summer through late fall and often affect more than a single horse on the farm during this time period.


  • In horses with serum hepatitis, clinical disease occurs 4-10 weeks after equine biologic administration; mean is approximately 6 weeks. The onset of liver disease prior to the onset of clinical signs is brief, 1-7 days.
  • Most clinically affected horses either die of hepatic failure or gradually recover over 5-10 days.
  • Recovered horses do not have chronic liver disease and there are no reports of hepatic neoplasia in horses recovering from Theiler's disease.


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login


This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Chandriani S et al (2013) Identification of a previously undescribed divergent virus from the Flaviviridae family in an outbreak of equine serum hepatitis. Proc Nat Acad Sci USA 110 (15), E1407-1415 PubMed.
  • Bergero D & Nery J (2008) Hepatic diseases in horses. J Anim Physiol Anim Nutr 92 (3), 345-355 PubMed.
  • Aleman M, Nieto J E, Carr A E et al (2005) Serum hepatitis associated with commercial plasma transfusion in horses. J Vet Intern Med 19 (1), 120-122 PubMed.
  • Buecher-Maxwell V, DiGrassie W, Dascanio J et al (2003) Measurements of Equine Serum Hepatic Indices after administration of tetanus antitoxin. J Equine Vet Sci 23, 220-224 VetMedResource.
  • Peek S F & Divers T J (2000) Medical treatment of cholangiohepatitis and cholelithiasis in mature horses - 9 cases (1991-1998). Equine Vet J 32 (4), 301-306 PubMed.
  • Giglick M A, MacAllister C G, Ely R W & Edwards W C (1995) Hepatic disease associated with administration of tetanus antitoxin in eight horses. JAVMA 206 (11), 1737-1740 PubMed.