Equine vaccine for West Nile virus.

The research reveals the development of a killed vaccine against West Nile Virus (WNV) for horses, which has proven safe and effective in generating an immune response and minimizing the occurrence of viraemia (the presence of the virus in the bloodstream).

About the West Nile Virus Vaccine

• The study aimed to develop a vaccine to control the infection of West Nile Virus (WNV) in horses.
• A killed form of the WNV was used to formulate the vaccine.
• The vaccine was administered twice, through intramuscular doses, at low, medium and high levels, with a three-week interval between the doses.

Dose Titration and Antibody Response

• The researchers initially conducted a dose titration study to assess the production of serum neutralizing antibodies against WNV in horses.
• Neutralizing antibodies are a part of the body’s immune response, and their presence signifies an effective reaction against the infectious agent – in this case, WNV.
• Serum samples were collected periodically for analysis using a plaque reduction neutralization test, a standard method for measuring the concentration of antibodies that can neutralize viruses.
• Significant increases in neutralizing antibodies were reported 14 days after the second dose across all dosage groups.

Experimental Challenge and Vaccine Efficacy

• A year after the second vaccination, both vaccinated and non-vaccinated horses were exposed to WNV.
• While a large percentage (81.8%) of the non-vaccinated horses developed viraemia, only a small percentage (5.3%) of the vaccinated horses showed transient viraemia.
• This result indicates a 94% preventable fraction, demonstrating the efficacy of the vaccine in preventing a systemic WNV infection.

Safety of the Vaccine

• A separate study was also carried out to evaluate the safety of the vaccine under actual field conditions.
• A total of 648 horses, including 32 pregnant mares, were part of the safety study.
• No adverse reactions were noted in 96% of the horses during the two weeks post-vaccination period. Mild, transient injection site reactions were seen in a small proportion of vaccinated horses.
• The absence of serious adverse reactions indicates that the vaccine is safe for use.

Conclusion

• The research, therefore, concludes that the killed WNV vaccine developed by Fort Dodge Animal Health was successful in provoking a significant immune response in vaccinated horses while maintaining a high level of safety.