Donkeys as reservoirs of African horse sickness virus.

This research paper investigates whether donkeys can function as long-term carriers for the African horse sickness (AHS) virus, despite not showing observable clinical signs. The study found that donkeys do become infected with the virus but do not seem to harbor it in the long term.

Objective and Methodology

• The objective of this investigation was to understand the role of donkeys in the spread of African horse sickness (AHS), a viral disease affecting equine species.
• Researchers focused primarily on AHS virus serotype 4 (AHSV 4), and they infected donkeys to observe their reaction, followed by normal ponies for comparison.
• The tested subjects were thoroughly observed for clinical signs, virus presence in the blood (viraemia) and tissue (tropism), as well as for any pathological changes in the tissues post-mortem.

Findings

• Despite neither fever nor other observable signs, donkeys were found to become infected with AHSV 4, developing a viraemia that persisted for up to 12 days. This viraemia, however, had a significantly lower concentration than that observed in similarly infected ponies.
• AHSV 4 showed a similar tendency to infect specific tissues (tissue tropism) in both the pony and the donkey, but it appeared to reproduce less efficiently in donkey tissues.
• The main pathological changes found in donkeys after death were increased fluid accumulation in the serosal lined compartments, particularly in the peritoneal cavity, and small and large spots of bleeding on the left hepatic ligament.

Conclusions

• Post-mortem findings from 6 donkeys inoculated with AHSV and observed at 14 and 19 days post-inoculation showed no trace of the virus or viral antigens in any of the collected tissues.
• These findings suggest that while donkeys are susceptible to AHS infection, they are unlikely to act as prolonged carriers of the virus.
• An interesting observation was made when two donkeys were subjected to a second virulent virus, AHSV 5—neither donkey’s blood had any evidence of the virus, despite previous inoculation with AHSV 4. It is speculated that a subsequent primary antibody response was generated against AHSV 5 in the tested donkeys.
• Finally, tissue from a donkey recently infected with AHSV 4, when inoculated into a susceptible pony, caused a fatal, cardiac form of AHS, confirming the contagious nature of AHS within equines and the utility of donkeys in its potential spread.