Virus previously linked to liver disease in horses appears to be largely harmless – study

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A virus previously linked by researchers to transmissible hepatitis in horses does not appear to be the cause of liver disease after all.

Transmissible hepatitis in horses, known as Theiler’s disease, has been known for 100 years without knowledge of the pathogen, or pathogens, that cause it.

Recently, two novel equine pegiviruses (EPgV) were discovered.

Whereas EPgV-1 was not associated with disease, the other was identified in an outbreak of acute serum hepatitis in horses, reported in a study in 2013. It was therefore named Theiler’s disease-associated virus (TDAV).

“This finding was surprising since human and monkey pegiviruses typically cause long-term infection without associated clinical disease,” Joy Tomlinson, Raphael Wolfisberg and their colleagues reported in the open-access journal, PLOS Pathogens.

Indeed, pegiviruses are generally not associated with clinical disease.

“Although no subsequent reports link TDAV to disease, any association with hepatitis has not been formally examined,” the study team noted.

The researchers from Denmark and the United States set out to learn more about EPgV-1 and TDAV, examining more than 20 tissue types from horses screened for the viruses.

“We consistently detected high viral loads only in serum, bone marrow and spleen, and viral RNA replication was consistently identified in bone marrow,” they reported.

Some blood cells and lymph nodes were sporadically positive, but not liver tissue.

The authors concluded that the two equine pegiviruses cause persistent infection in horses, but they are not associated with hepatitis.

They appear to have an affinity with bone marrow. This was identified as the primary site of replication for both viruses. There was no evidence of replication in the liver.

“These findings call into question the connection between TDAV, liver infection, and hepatitis in horses,” they reported. “Based on these findings, it may be appropriate to rename the group of TDAV and related viruses as EPgV-2.

“Collectively, these findings are highly indicative that EPgVs are not associated with liver disease, but are bone marrow tropic and non-pathogenic.”

The study team noted that a recently discovered parvovirus (EqPV-H) appears to be responsible for several Theiler’s disease cases in horses. It has been identified in many investigated cases of acute serum hepatitis, as well as other cases of acute liver disease in horses, they said.

The 17-strong study team hailed from a range of institutions, including Cornell University in New York, the University of Copenhagen in Denmark, the Rockefeller University in New York, and the Research Institute at the Nationwide Children’s Hospital in Columbus, Ohio.

Tomlinson JE, Wolfisberg R, Fahnøe U, Sharma H, Renshaw R, Nielsen L, et al. (2020) Equine pegiviruses cause persistent infection of bone marrow and are not associated with hepatitis. PLoS Pathog 16(7): e1008677. https://doi.org/10.1371/journal.ppat.1008677

The study, published under a Creative Commons License, can be read here

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