Development and Preclinical Evaluation of a Lyophilized Vaccine Against Equine Herpesvirus Type 4 (EHV-4).

The research article discusses the development and evaluation of a freeze-dried vaccine for equine herpesvirus type 4 (EHV-4), a serotype responsible for equine rhinopneumonia, mainly in Kazakhstan. The vaccine, developed using attenuated EHV-4 and various stabilizers, showed promising outcomes for safety, stability, longevity, and immunogenicity.

Vaccine Development

• The scientists emanate from an existing EHV-4 strain, which underwent attenuation through serial passaging in primary lamb testicle cell cultures. This process generates a less virulent form of the virus that could activate the immune response without causing disease.
• The resulting viral biomass was then mixed with different stabilizers and freeze-dried, creating a lyophilized vaccine. The lyophilization helps extend the vaccine’s shelf life and improves its thermotolerance, crucial for regions with challenging storage conditions.
• Following a series of tests, the researchers selected a combination of sucrose, gelatin, and lactalbumin hydrolysate as the most effective stabilizers, as it ensured the highest retention of viral titer post lyophilization.

Numerous Stages of Evaluation

• Mice, guinea pigs, rabbits, donkeys, and horses were used to assess the vaccine’s safety and immunogenicity.
• The evaluation revealed that the vaccine retained infectivity for at least six months at 4° Celsius, making it suitable for climates with limited cold-chain infrastructure.
• All test species showed no adverse clinical signs, suggesting the vaccine’s safety.
• Furthermore, immunized animals demonstrated strong neutralizing antibody responses, establishing the vaccine’s immunogenicity (ability to provoke an immune response).

Protective Efficacy

• A reproductive challenge model with guinea pigs was utilized to evaluate the vaccine’s protective efficacy. After being vaccinated and then exposed to a virulent EHV-4 strain, all pregnant females retained their pregnancies, showing complete fetal viability.
• This outcome suggests the potential value of the vaccine in preserving animal health and preventing economic loss due to disease-induced abortions in the equine industry.

Conclusion

• Overall, this research presents a promising candidate for a freeze-dried, live-attenuated EHV-4 vaccine.
• Its safety profile, immunogenicity, thermotolerance, and protective efficacy, particularly against fetus loss during pregnancy, make it a beneficial tool for preventing EHV-4 infections, notably in young horses and in regions with limited cold-chain capacities.