Immunologic relationships between equine herpesvirus type 1 (equine abortion virus) and type 4 (equine rhinopneumonitis virus).

The research aims to examine the immune responses in foals to equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4). They concluded that a bivalent vaccine, containing both EHV-1 and EHV-4, may be more efficient for disease control than the currently used EHV-1 alone.

Experiment Design and Methodology

• The study involved three colostrum-deprived specific-pathogen-free foals. This means they were free of any specific pathogens prior to the vaccine. The foals were deprived of colostrum to prevent interference from any maternal antibodies that could skew the results.
• One foal was vaccinated with inactivated EHV-1, another with inactivated EHV-4, while the third one was given a control cell lysate plus an adjuvant. An adjuvant is a substance that boosts the body’s immune response to the vaccine.
• This was followed by exposure to EHV-1 and EHV-4 via intranasal challenge exposure techniques to test the response of the immune system.

Findings

• Vaccination with the inactivated virus preparations induced a cellular immune response as well as the production of antibodies. The challenge exposures further increased this response.
• Cellular immune responses, as measured by in vitro lymphocyte blastogenesis (a process that measures the ability of lymphocytes to replicate), were cross-reactive regardless of the strain of EHV administered. This means that the foals’ immune systems responded similarly to both EHV-1 and EHV-4.
• However, virus-neutralizing antibodies in the serum were type-specific in foals given EHV-1 but were cross-reactive after EHV-4 administration. This means that the antibodies produced in response to EHV-1 were specific to the virus and did not react with EHV-4, but the antibodies produced in response to EHV-4 were capable of neutralizing both viruses.

Conclusion

• These findings led the researchers to suggest that a combined or “bivalent” vaccine containing both EHV-1 and EHV-4 would potentially be a more effective method of controlling diseases caused by the equine herpesvirus than the existing vaccines that contain only EHV-1.