A field study of persistence of antibodies in California horses vaccinated against western, eastern, and Venezuelan equine encephalomyelitis.

The research investigates the persistence of antibodies in vaccinated horses against various types of equine encephalomyelitis in California, and evaluates the feasibility of incorporating revaccination against Venezuelan equine encephalomyelitis (VEE) into routine vaccination practices.

Study and Findings

• The study was set in the backdrop of an ongoing threat of Venezuelan equine encephalomyelitis (VEE), a highly infectious and often fatal disease for horses to understand the effectiveness of its vaccine and evaluate if it could be combined with routine vaccinations.
• The experiment involved horses who were given an annual vaccination for two types of encephalomyelitis – western equine encephalomyelitis (WEE) and eastern equine encephalomyelitis (EEE). It was observed that 57% of these horses retained detectable serum-neutralizing (SN) antibody titers for VEE 18 months after the initial VEE vaccination was given.
• 100% of the horses with no record of previous WEE-EEE vaccination retained detectable VEE SN antibody titers over the same 18 months period.
• In absolute terms, the VEE antibody titer was 25 times higher in horses not previously vaccinated against WEE-EEE as compared to the horses that were given the annual WEE-EEE vaccination at the time of VEE vaccination.

Implication

• These findings indicate that the common antigens that trigger immune response in case of VEE could possibly be present in bivalent WEE-EEE vaccine as well. This was evidenced by a sharp increase in VEE geometric mean titer from 4 to 70 at 48 days after initial WEE-EEE vaccination in horses previously vaccinated against VEE.
• Consequently, the study concluded that the most effective serum-neutralizing (SN) antibody response to VEE revaccination occurred when VEE vaccine was administered simultaneously with the bivalent WEE-EEE vaccine.
• A total of 150 serum samples were tested by both the SN and the hemagglutination-inhibiton tests which rendered a comparative result of 70% for VEE, 81% for EEE, and 87% for WEE at greater than or equal to 1:10.

Summary

• This study could potentially guide a policy change relating to equine vaccinations, implying that the revaccination for VEE and annual WEE-EEE vaccinations could be given together. This has wider ramifications for disease control and animal health management.