Differential responses of Equus caballus and Equus asinus to infection with two pathogenic strains of equine infectious anemia virus.

This research examines the variation in reactions of horses (Equus caballus) and donkeys (Equus asinus) when infected with two strains of the disease-causing equine infectious anemia virus. It was found that although the horses demonstrated discernible disease symptoms, the donkeys remained largely asymptomatic, suggesting that factors other than host cell permissiveness might influence the observed clinical disparities.

Study Design and Methodology

• This study investigated the responsivity difference by infecting both horses (ponies included) and donkeys with two strains of equine infectious anemia virus (EIAV) known as EIAV(PV) and EIAV(WY), viruses reported to induce disease in horses.
• Four ponies and two donkeys were infected with the EIAV(PV) strain, while one horse and one donkey were infected with the EIAV(WY) strain.
• Following infection, the animals were observed for a 365-day period to assess and record any clinical indications of the disease.

Clinical Observations and Findings

• While all horses showed discernible disease signs, some quite severe, the donkeys remained asymptomatic except for minor temporary reductions in platelet counts.
• Test results from serological assays, virus isolation from plasma, and plasma-associated viral RNA detection using RT-PCR, indicated that initial replication of both EIAV(PV) and EIAV(WY) was less in donkeys than in horses.
• This conclusion was supported by competitive RT-PCR, which revealed that viral RNA levels in the plasma of infected ponies were up to 100,000 times higher than that in infected donkeys during the first 20 days post-infection.

In-vitro Experiments and Conclusions

• Through in-vitro infection of donkey and horse monocyte-derived macrophage cultures with EIAV(PV), it was shown that these cells were equally susceptible to virus-induced cytopathic effects and produced comparable levels of offspring virus.
• These findings suggest that factors other than host cell receptivity might be responsible for the observed clinical variations between horses and donkeys infected with EIAV(PV) or EIAV(WY).
• The differential responses of the animals could be a result of differences in immune system reactions, suggesting an avenue for further research into the nature of disparity and possible prevention strategies for equine infectious anemia.