Hepatitis C Virus in Horses

For many years there were no known relatives of Hepatitis C Virus that infected other species than primates. Then news arrived that a related virus was found in dogs (Canine Hepatitis C Virus or Canine Hepacivirus)[1]. Somewhat later variants were discovered in rodents (Murine Hepatitis C Virus or Murine Hepacivirus)[2] and horses (Equine Hepatitis C Virus or Equine Hepacivirus).

Equine Hepatitis C Virus or Equine Hepacivirus is a member of the Flaviviridae family that infects horses. Though the virus itself was known for some time, direct evidence that it causes hepatitis in horses was lacking. However, recently Equine hepacivirus was discovered in two horses that developed post-transfusion hepatitis. Plasma and serum from these horses were then used to experimentally transmit the virus to four other (already very ill) horses[3].

The result of that experiment demonstrated that Equine Hepatitis C Virus had infection kinetics similar to (Human) Hepatitis C Virus and that infection was associated with acute and chronic liver disease.

Although most of the animals were coinfected with Equine Pegivirus (EPgV), also a flavivirus, EPgV viral loads were much lower and often undetectable in both liver and blood.

To date, researchers found no less than eight closely related Hepatitis C Viruses in horses. Although most of these serotypes detected were genetically distinct from Canine Hepatitis C Virus infecting dogs, one (from New Zealand) was almost identical, providing evidence for an ability of Non-Primate Hepatitis Viruses (NPHVs) to jump species.

The fact that Hepatitis C Viruses in horses are found in geographically distinct areas suggests that horses are a reservoir of Non-Primate Hepatitis Viruses (NPHVs). It seems likely that dogs might acquire their NPHV infection from horses, as there are always ample opportunities for contact between the two animals on farms or in kennels.

It will be important to determine if Equine Hepatitis C Virus was the source of Human Hepatitis C Virus. There are six genotypes of Human Hepatitis C Virus, each of which is believed to have emerged at different times and geographic locations. Whether their emergence represent different cross-species transmissions remains to be determined[4].

[1] Kapoor et al: Characterization of a canine homolog of hepatitis C virus in Proceedings of the National Academy of Sciences - 2011
[2] Drexler et al: Evidence for novel hepaciviruses in rodents in PloS Pathogens - 2013
[3] Ramsay et al: Experimental transmission of equine hepacivirus in horses as a model for hepatitis C virus in Hepatology – 2015
[4] Scheel et al: Surveying the global virome: identification and characterization of HCV-related animal hepaciviruses in Antiviral Research - 2015