Protection of horses from West Nile virus Lineage 2 challenge following immunization with a whole, inactivated WNV lineage 1 vaccine.

This research investigates the effectiveness of a West Nile virus (WNV) vaccine, originally developed to tackle its Lineage 1 form. The study finds that this established vaccine can also provide protection against the newer Lineage 2 variant of WNV that has spread from Africa to Europe.

Study Overview

• The research involved 20 horses that had never been infected by WNV. They were divided into two groups: the first group remained unvaccinated (T01), and the second group was vaccinated with the Equip WNV vaccine (T02).
• Each horse in the vaccination group was given two doses of the vaccine on day 0 and day 21, and then all horses were exposed to WNV Lineage 2 on day 42.
• Throughout the study, the researchers who were taking clinical readings were not made aware of which horses had been vaccinated and which had not, to ensure the results remained unbiased.

Findings

• 60% of the unvaccinated horses had to be euthanized after exposure to the virus, while none of the vaccinated horses required euthanization.
• The percentage of sickness instances among vaccinated horses was significantly lower when compared to the unvaccinated horses.
• While 80% of the unvaccinated horses were infected and showed a presence of the virus in their bloodstream (viremia), only one vaccinated horse tested positive in a single occurrence.

Antibody Response and Histopathology Scores

• Vaccinated horses began creating antibodies against WNV Lineage 2 starting from day 14, that is, two weeks after receiving the initial dose of vaccine. By day 42, the time at which the horses were exposed to the virus, all vaccinated horses had developed a strong antibody response.
• A histopathology examination, which looks at microscopic changes in tissues due to disease, showed all unvaccinated horses had degrees of damage that ranged from mild to severe in sampled tissues (cervical spinal cord, medulla, and pons).
• On the other hand, eight out of ten vaccinated horses showed no tissue damage; the remaining two had minimal lesions in one tissue type.

Conclusion

The study concluded that the Equip WNV vaccine, initially formulated to combat Lineage 1 of West Nile virus, is also significantly effective in reducing the presence of virus in the blood, the duration and severity of disease symptoms, and mortality rates in horses exposed to WNV Lineage 2.