Equine herpesvirus type 2: cell-virus relationship during persistent cell-associated viremia

Area of Science:

• Veterinary Virology
• Immunology
• Equine Infectious Diseases

Background:

• Equine herpesvirus type 2 (EHV-2) causes persistent, cell-associated viremia.
• Understanding the latent stage of EHV-2 infection is crucial for managing equine health.

Purpose of the Study:

• To investigate the biology of EHV-2 during its persistent cell-associated viremia stage.
• To develop and validate a method for enumerating latently infected leukocytes.

Main Methods:

• Developed and utilized an infective center (IC) assay to quantify latently EHV-2 infected leukocytes.
• Assessed the relationship between cell density, IC plaque formation, and EHV-2 infection.
• Correlated serum-neutralization titers with IC numbers.
• Attempted transmission of EHV-2 via infected leukocytes to equine fetuses.

Main Results:

• The IC assay was simple, reproducible, and showed a linear relationship between cell number and plaques, except at high cell densities.
• Significant variation in IC counts was observed between different horses, but consistency within individual horses over time.
• A direct correlation was found between serum-neutralization titers and IC counts.
• Transfer of infected leukocytes did not establish EHV-2 infection in fetuses.
• EHV-2 infection did not induce detectable Fc receptors on equine fetal kidney cells.

Conclusions:

• The developed IC assay is a reliable tool for quantifying latent EHV-2 infected leukocytes.
• EHV-2 exhibits significant inter-horse variability in latent viremia.
• Serum-neutralization titers may reflect the level of latent EHV-2 infection.
• Cell-associated EHV-2 viremia in leukocytes may not be efficiently transmitted vertically, and EHV-2 does not induce Fc receptors on equine fetal kidney cells.