The complete genome of equid herpesvirus-1 (EHV-1) field isolates from Argentina reveals an interspecific recombinant strain.

Overview

• This study sequenced and analyzed the complete genomes of two equid herpesvirus-1 (EHV-1) isolates from Argentina, revealing that one is a recombinant strain with genetic material from a related virus, Equid alphaherpesvirus-4 (EHV-4).
• The findings offer new insights into viral diversity and evolution in EHV-1 strains circulating in South America and highlight the occurrence of interspecific recombination events.

Background

• Equid alphaherpesvirus type 1 (EHV-1) is a virus that infects horses and can cause serious health problems including abortions, death of newborn foals, and neurological disease (myeloencephalopathy).
• Such infections have significant economic consequences for the horse industry worldwide due to outbreaks affecting reproduction and health.
• Understanding the genomic makeup of EHV-1 strains helps in disease control, vaccine development, and understanding virus evolution.

Objective

• To obtain and analyze the complete genome sequences of EHV-1 isolates from Argentina, a region previously lacking representative complete viral genomes in public databases.
• To characterize any genetic variations or recombination events that might be present in these field isolates.

Methods

• Two virus isolates, named E/745/99 and E/1297/07, were obtained from aborted horse fetuses in Argentina.
• Complete genome sequencing of these isolates was performed, allowing comparison to known EHV-1 reference strains and detection of recombination events.
• Bioinformatic analyses included sequence identity comparisons, identifying genetic breakpoints, and examining tandem repeat sequences.

Key Findings

• Genome Comparisons:
  • The E/745/99 isolate’s genome showed 98.2% sequence identity with Ab4, a well-characterized reference strain of EHV-1.
  • The E/1297/07 isolate’s genome shared 99.8% identity with NY03, a known recombinant EHV-1 strain from the US.
• Recombinant Strain Identification:
  • The E/1297/07 isolate was found to be an interspecific recombinant strain containing DNA sequences derived partially from EHV-4, a related but distinct equid herpesvirus species.
  • Specifically, recombination was found in part of the ORF64 gene and an adjacent intergenic region.
  • The recombination breakpoints in E/1297/07 matched those previously identified in US and Japanese recombinant strains such as NY03.
• Variability in Recombinant Regions:
  • These recombinant genomic segments showed variation in the numbers of tandem repeats and minor parental sequences originating from EHV-4.
  • This suggests that multiple, distinct recombination events between EHV-1 and EHV-4 have independently occurred.
• Novelty and Significance:
  • This is the first report of complete EHV-1 genomes from Argentine and South American isolates deposited in public databases, expanding global viral genome data.

Implications

• The discovery of a recombinant EHV-1 strain in Argentina with genetic contributions from EHV-4 enhances understanding of herpesvirus evolution and viral diversity in horses.
• Recombination between related herpesviruses may impact viral pathogenicity, immune evasion, or transmission, influencing outbreak dynamics.
• Sharing these complete genomes publicly benefits global research efforts in diagnostics, epidemiology, and vaccine design for equine herpesviruses.
• Further surveillance and genomic studies are warranted to monitor recombinant strains and their potential impact on animal health.