Resistance of castrated male horses to attempted establishment of the carrier state with equine arteritis virus.

This research studied the resistance of castrated male horses (geldings) to the equine arteritis virus (EAV), demonstrating that geldings are less likely to harbor a persistent infection of EAV due to the role of testosterone in the establishment and maintenance of the virus carrier state.

Study Method and Procedure

• The authors tested the vulnerability of twelve geldings to EAV by intranasally inoculating them with the KY-84 strain of the virus. This strain had previously been shown to be capable of creating a persistent carrier state in stallions.
• Following the inoculation, the researchers monitored the animals for clinical signs of equine viral arteritis (EVA), periods of fever or viremia (the presence of viruses in the blood), and nasal shedding of the virus. These observations were made to assess the course of infection and the body’s response to the virus.

Observations and Results

• Except for one horse that only developed a fever, all of the geldings presented with characteristic clinical signs of EVA.
• The infected geldings experienced periods of fever ranging from 2 to 10 days post inoculation. Viremia was observed from day 2 onwards, lasting between 9 to at least 19 days. Nasal shedding of the virus began 2-4 days after inoculation, indicating the period of active infection and potential contagion, and continued for 7 to 14 days.
• All geldings had seroconverted to EAV by day 11, showing an immune response against the virus. The serum neutralization titres, a measure of the immune response, ranged from 8 to 64. After 4 weeks, the titres were between 8 and 32, indicating a gradual decrease in the immune response over time.
• Trace amounts of EAV were found in the kidney and blood of one horse euthanized 30 days after inoculation, and in the blood of another horse euthanized after 57 days. However, no virus was isolated from any tissue or fluid sample collected from the remaining ten geldings, all of which were euthanized between days 30 and 148.

Research Conclusion

• The researchers concluded that the lack of EAV persistence in geldings supports previous studies indicating testosterone’s essential role in establishing and maintaining the viral carrier state. This finding indicates that castrated male horses are less likely to become long-term carriers of EAV, potentially contributing to disease control strategies.