Donkeys appear to be a natural host for the liver-affecting equine hepacivirus (EqHV), researchers in Germany report. They found that the virus infects both donkeys and horses in a similar way.
The virus was originally found to infect horses. However, it was recently also found in donkeys following the testing of blood samples collected between 1974 and 2016 in Germany, Spain, Bulgaria, Italy, France, Mexico, and Bulgaria.
In that study, viral loads were found to be comparable in both species, but slightly elevated levels of serum liver enzymes were apparent only in horses.
While the seroprevalence in donkeys (31.5% of 882 samples) was comparable to that of horses (30 to 40% in North America or Europe), viral RNA was detected in only three of the donkeys (0.3%), as opposed to 2 to 8% in horses.
André Gömer and his fellow researchers, writing in the journal One Health Outlook, said the absence of chronically infected donkeys and the lower rate of EqHV RNA-positive donkeys suggests the disease might be acute rather than persistent in the species. It also raises speculation over whether donkeys might be more resistant to the virus.
In their study, they inoculated two adult female donkeys and one control horse intravenously with the virus from a naturally infected horse in order to analyze the susceptibility and the course of EqHV infection. Liver biopsies were taken before and after inoculation to study changes.
“We were able to show that EqHV infects both donkeys and horses in a similar fashion,” the researchers reported. The course of EqHV-RNA levels was almost identical, they said, suggesting donkeys might be a natural host of this virus.
All animals were EqHV PCR-positive from day three. EqHV RNA-levels declined when the animals seroconverted and both donkeys cleared the virus from their blood by week 12. Liver enzymes serum levels were slightly elevated in the horse at the time of seroconversion, less so in the donkeys.
Infection did not have an impact on clinical findings and no significant liver differences were seen.
“Overall, we were able to show that immune responses, especially towards viral defense, were more pronounced in the horse than in the donkeys.”
Notably, one donkey showed only a weak response in general, while the other donkey mounted a stronger immune response.
“Interestingly, even though donkey 1 had a weak immune response and the slowest seroconversion, it was able to clear the infection within the same timeframe as donkey 2. This might indicate that other factors which were not activated at this early state within the liver, such as the adaptive immunity, were strongly involved in viral clearance.”
They subsequently analyzed the RNA response in pre and post-infection liver biopsies. Distinct patterns for each animal were detected instead of a uniform set of genes associated with disease or clearance, suggesting different mechanisms in reacting to hepaciviral infections between the animals.
The study team comprised Gömer, Christina Puff, Birthe Reinecke, Stephanie Bracht, Maria Conze, Wolfgang Baumgärtner, Jörg Steinmann, Karsten Feige, Jessika Cavalleri, Eike Steinmann and Daniel Todt, variously affiliated with the University of Veterinary Medicine Hannover, the Twincore Center for Experimental and Clinical Infection Research, the University of Duisburg-Essen and Ruhr University Bochum, all in Germany; and the University of Veterinary Medicine Vienna in Austria.
Gömer, A., Puff, C., Reinecke, B. et al. Experimental cross-species infection of donkeys with equine hepacivirus and analysis of host immune signatures. One Health Outlook 4, 9 (2022). https://doi.org/10.1186/s42522-022-00065-y