Immunologic responses to West Nile virus in vaccinated and clinically affected horses.

The research compares the antibody response in horses that have been vaccinated against West Nile Virus (WNV) and horses that survived the disease naturally. It finds that some horses responded poorly to the vaccination, suggesting that more frequent vaccinations and other preventive measures may be needed.

Research Methods

• A cross-sectional observational study was conducted on 187 horses vaccinated with a killed WNV vaccine and 37 horses with confirmed clinical WNV infection.
• Serum from vaccinated horses was collected twice: once before and once 4 to 6 weeks after the initial vaccination. This was followed by another collection 5 to 7 months later.
• For horses that survived the infection, serum was collected 4 to 6 weeks after they were diagnosed and 5 to 7 months after the first sample was taken.
• The team utilised three tests for their analysis: the IgM capture ELISA, plaque reduction neutralization test (PRNT), and microtiter virus neutralization test.

Research Findings

• All horses that had survived the disease were found to have PRNT titers equal or higher than 1:100 at 4 to 6 weeks post-infection. 90% of them maintained this titer for 5 to 7 months.
• Post the second vaccination, 67% of vaccinated horses exhibited PRNT titers equal or higher than 1:100. However, 14% had considerably lower titers (< 1:10).
• 5 to 7 months later, only 33% of the vaccinated horses retained a PRNT titer of 1:100 or more. 29% showed much lower titers (< 1:10).
• The horses’ end point titers had dropped by 5 to 7 months post-vaccination regardless of whether they were vaccinated or naturally infected.

Conclusion

• The study concluded that a portion of horses vaccinated against WNV showed poor response. This suggests a need for more regular vaccinations—possibly as often as every 6 months—in some horses and in high-risk areas.
• Given the inconsistent vaccine response, additional preventative measures, like mosquito control, are recommended to inhibit WNV infection in horses.