Induction of immune response and protection from equine viral arteritis (EVA) by formalin inactivated-virus vaccine for EVA in horses.

The research is about the testing and effectiveness of a vaccine against equine viral arteritis (EVA) in horses, including pregnant mares. The study demonstrates how the vaccine’s repetitive use can elicit a strong and persistent immune response, providing protection from the disease and preventing abortion in pregnant mares.

Methodology

• The trial involved thirty-nine horses, including three pregnant mares, which were all vaccinated with a formalin inactivated-virus vaccine for EVA.
• The vaccine efficacy was tested by administrating singular and multiple doses over specific time intervals. The antibody response was then gauged in terms of serum neutralizing (SN) titers, a measurement used to evaluate the amount of functional antibodies a patient’s blood can produce against a specific antigen.

Summary of Results

• After the first single dose of the vaccine, the resultant antibody response was found to be somewhat weak, indicating that the effective inoculum dose should contain 10(8.4) plaque-forming units (pfu) of virus before inactivation.
• A more robust immune response was observed when two doses of the vaccine were given, with a four-week gap between them. The horses developed high SN antibody titers (up to a dilution of 1:5,120).
• However, the elevated SN titers declined fairly rapidly over time. When supplemental doses were applied after two months, a quicker antibody response was provoked and steadier SN titers were maintained (ranging between 1:80 to 1:320) six months after the administration.

Conclusions and Recommendations

• The research indicates that repeated (every six months to one year) administrations of the EVA vaccine can maintain high SN antibody titers that provide immunity against EVA.
• The vaccine also protected the horses from showing clinical signs of EVA and, significant for the pregnant mares in the study, prevented abortion following exposure to the virulent virus.
• Clinical signs and viremia confirmed the protective dose, giving an SN titer of 1:43 as the fifty percent protective titration.