Identification of neuropathogenic Varicellovirus equidalpha1 as a potential cause of respiratory disease outbreaks among horses in North Xinjiang, China, from 2021-2023.

Overview

• This study reports the first documented outbreak of respiratory disease in horses in China caused by Varicellovirus equidalpha1 (EqAHV-1), a virus known to cause respiratory issues globally in equine populations.
• It identifies the virus as neuropathogenic, meaning it has the potential to affect the nervous system, based on genetic analysis of viral strains collected during the outbreak in North Xinjiang between 2021 and 2023.

Background

• Varicellovirus equidalpha1 (EqAHV-1), formerly known as Equid alphaherpesvirus 1, is a significant infectious agent in horses worldwide, causing respiratory and neurological diseases.
• Prior to this study, there were no reports linking EqAHV-1 with respiratory disease outbreaks in horses located in China.
• Horses in North Xinjiang experienced an outbreak of respiratory illness from April 2021 to May 2023, prompting investigation into the causative agents.

Objectives

• To identify and confirm the viral pathogens responsible for the respiratory disease outbreak among horses in North Xinjiang.
• To characterize the genetic features of the identified EqAHV-1 strains to assess their neuropathogenic potential.
• To understand the epidemiological link and origin of these horse herpesvirus strains within the region.

Methods

• Samples were collected from horses showing respiratory disease symptoms during the outbreak period.
• Quantitative Polymerase Chain Reaction (qPCR) assays were performed to detect the presence of different Equid alphaherpesviruses including EqAHV-1, EqAHV-2, EqAHV-4, and EqAHV-5.
• Three EqAHV-1 viral strains were successfully isolated from affected horses.
• Full-length ORF33 gene sequences of these strains were compared with known sequences from previous isolates, including those from aborted horses in the Yili region.
• Phylogenetic analyses were conducted to explore genetic relationships and trace origins of these virus strains.
• Genetic analysis of the ORF30 gene, which encodes viral DNA polymerase, was carried out to identify markers associated with neuropathogenicity, focusing on the nucleotide position 2254.

Key Findings

• EqAHV-1 was detected in all samples, confirming its presence in horses exhibiting respiratory symptoms during the outbreak.
• Other related herpesviruses (EqAHV-2, EqAHV-4, and EqAHV-5) were present in only a limited number of samples, suggesting EqAHV-1 as the principal respiratory pathogen in this outbreak.
• ORF33 sequence comparisons indicated that the isolated EqAHV-1 strains likely shared origins with strains previously linked to abortion cases in horses from the Yili region, suggesting regional viral circulation or spread.
• ORF30 sequence analysis identified a guanine (G) residue at nucleotide position 2254, which translates into aspartic acid at amino acid position 752 of the viral DNA polymerase protein; this is a known marker of neuropathogenic strains.
• This genotype is associated with more severe neurological impact and potentially increased virulence of the virus.

Conclusions and Implications

• This study is the first to report EqAHV-1 as the cause of an equine respiratory disease outbreak in China, expanding geographic and epidemiological knowledge of the virus.
• The isolated strains harbor a neuropathogenic genotype, indicating that the virus not only causes respiratory illness but also has the potential to cause neurological disease in horses.
• The findings highlight the importance of continuous surveillance and molecular characterization of equine herpesviruses to monitor and control outbreaks.
• Given the neuropathogenic potential, veterinary practitioners and horse owners should be vigilant about EqAHV-1 infections, considering both respiratory and neurological complications.
• This research sets a baseline for future studies in China to explore virus evolution, spread, and vaccine development targeting these pathogenic strains.