Pathogenicity and immunogenicity of equine herpesvirus type 1 mutants defective in either gI or gE gene in murine and hamster models.

The study presents the development and testing of two equine herpesvirus type 1 (EHV-1) mutants used to create a live vaccine for the virus. Though these mutants showed reduced cell-to-cell spread, they were just as capable of growth in-vitro as the parental EHV-1 strain and were less virulent in animal models. However, they still produced an immune response that helped clear out the parental virus.

Construction and observation of EHV-1 mutants

• The researchers created two EHV-1 mutants, called DeltagI and DeltagE. Each had deletions in either the glycoprotein I (gI) or E (gE) gene respectively.
• In comparison to the parental and revertant strains, these mutants created smaller plaques in equine cell culture.
• The growth patterns of the mutants and the parental strain were virtually the same when cultured. This indicates that while gI and gE contribute to the EHV-1’s ability to spread from cell to cell, they are not necessary for in-vitro viral growth.

Testing of EHV-1 mutants in animals

• Mice and hamsters that were intranasally inoculated with the DeltagI and DeltagE mutants did not show any clinical symptoms and continued to gain weight.
• Comparatively, animals inoculated with the parental virus displayed a decrease in average body weight. Nervous symptoms were also observed in hamsters infected with the parental EHV-1.
• This suggests that gI and gE play a significant role in EHV-1’s virulence and neurovirulence in experimental animal models.

Immune response to EHV-1 mutants

• Serum neutralizing antibodies against EHV-1 were found in mice that had been immunized with either DeltagI or DeltagE, two weeks post-inoculation.
• When challenged with the parental virus, these immunized mice were able to clear the virus from their lungs quicker than mice that had not been immunized (mock-immunized mice).
• This indicates that the EHV-1 mutants are attenuated but still able to elicit an immune response in the inoculated animals, aiding in virus clearance.