Experimental cross-species infection of donkeys with equine hepacivirus and analysis of host immune signatures

Abstract

Background The Equine Hepacivirus (EqHV) is an equine-specific and liver-tropic virus belonging to the diverse genus of Hepaciviruses. It was recently found in a large donkey (Equus asinus) cohort with a similar seroprevalence (30%), but lower rate of RNA-positive animals (0.3%) compared to horses. These rare infection events indicate either a lack of adaptation to the new host or a predominantly acute course of infection. Methods In order to analyze the susceptibility and the course of EqHV infection in donkeys, we inoculated two adult female donkeys and one control horse intravenously with purified EqHV from a naturally infected horse. Liver biopsies were taken before and after inoculation to study changes in the transcriptome. Results Infection kinetics were similar between the equids. All animals were EqHV PCR-positive from day three. EqHV RNA-levels declined when the animals seroconverted and both donkeys cleared the virus from the blood by week 12. Infection did not have an impact on the clinical findings and no significant histopathological differences were seen. Blood biochemistry revealed a mild increase in GLDH at the time of seroconversion in horses, which was less pronounced in donkeys. Transcriptomic analysis revealed a distinct set of differentially expressed genes, including viral host factors and immune genes. Conclusion To summarize, our findings indicate that donkeys are a natural host of EqHV, due to the almost identical infection kinetics. The different immune responses do however suggest different mechanisms in reacting to hepaciviral infections.

Dose-Dependent Hepacivirus Infection Reveals Linkage between Infectious Dose and Immune Response

“…On the other hand, adaptive immune responses were shown to have a strong effect on virus replication. In this and previous studies, virus copy numbers decrease with the appearance of anti-EqHV antibodies ( 18 – 20 , 26 , 32 ). Similarly, HCV in chimpanzees and humans is often eliminated with co-occurrence of strong adaptive immune responses ( 38 , 55 , 56 ).…”

“…In previous EqHV infection studies, most animals were acutely infected and prolonged viremia was rarely observed. Inoculation techniques have varied, with inoculation volumes ranging from 1 to 500 mL serum or plasma, corresponding to approximately 2 × 10 4 to 3.9 × 10 9 RNA copies per infection ( 19 , 20 , 26 , 32 ). In addition, inoculation with serum or plasma often has the disadvantage that the host immune system, especially at high doses, could trigger an early and strong immune response that contributes to viral clearance.…”

“…In addition, inoculation with serum or plasma often has the disadvantage that the host immune system, especially at high doses, could trigger an early and strong immune response that contributes to viral clearance. To circumvent this, the viral inoculum can be ultracentrifuged to remove serum components, or in vitro -transcribed RNA can be injected intrahepatically ( 25 , 32 ). In our study, we inoculated with small amounts of plasma in the low-dose infections, which may prevent strong immune activation by plasma components and thus contribute to sustained viral replication.…”

“…Equids have been experimentally inoculated with EqHV in several studies ( 19 , 20 , 25 , 26 , 32 ). However, the majority of inoculated horses developed a self-limited acute infection, and only horses 8 months of age or younger—a phase in which the equid immune system is not fully developed yet—were persistently infected ( 20 , 22 ).…”