Equine gamma herpesvirus presence and viral load are not associated with equine glandular gastric disease.

Overview

• This study investigated whether equine gamma herpesviruses (EHV-2 and EHV-5) are associated with equine glandular gastric disease (EGGD) by measuring their presence and quantity in affected and normal stomach tissues of horses.
• The research also examined the microscopic tissue changes in the glandular part of the horse’s stomach in cases of EGGD.

Background

• Equine glandular gastric disease (EGGD) is a condition affecting the glandular mucosa (inner lining) of horses’ stomachs, often characterized by inflammation or ulcers.
• Equine herpesviruses 2 and 5 (EHV-2 and EHV-5) are gamma herpesviruses commonly found in horses; their potential involvement in EGGD had not been thoroughly investigated.
• The study aimed to explore whether the presence or amount of these viruses is linked with the development or severity of EGGD, which could suggest a viral role in the disease.

Study Design and Methods

• A total of 29 horses were included: 21 sampled postmortem and 8 via gastroscopy (an internal stomach examination).
• Horses were categorized into three groups:
  • Normal (11 horses) – no gastric disease.
  • EGGD only (12 horses).
  • Both EGGD and equine squamous gastric disease (6 horses).
• Samples of glandular gastric mucosa were collected either through gastroscopy during life or postmortem from the stomach lining.
• Histopathological analysis was performed to assess tissue abnormalities under a microscope.
• In situ hybridization, a technique that detects specific viral DNA or RNA within tissue cells, was used to localize and quantify EHV-2 and EHV-5 in the samples.
• The number of cells positive for viral presence was counted per square millimeter of tissue.
• Examiners analyzing tissue and viral load data were blinded to the horses’ disease status to avoid bias.

Results

• Surprisingly, normal (non-EGGD) horses had higher viral loads in their glandular stomach mucosa compared to both normal and abnormal tissues from horses with EGGD.
• Within horses diagnosed with EGGD, there was no significant difference in viral loads between grossly or endoscopically normal versus abnormal glandular mucosa.
• This suggests that the presence and quantity of EHV-2 and EHV-5 are not associated with the appearance or severity of EGGD lesions.
• The most common microscopic abnormality found in horses with EGGD was lymphocytic plasmacytic gastritis, indicating an inflammatory process dominated by these immune cells.
• Only 3 horses showed mucosal disruption in the form of ulcers or erosions, indicating that mucosal damage is not always present in EGGD.

Conclusions

• The study concludes that equine gamma herpesviruses EHV-2 and EHV-5 are unlikely to contribute to the development or pathology of equine glandular gastric disease.
• EGGD appears primarily to be an inflammatory condition in the glandular stomach mucosa, sometimes accompanied by mucosal damage such as ulcers or erosions.
• These findings help clarify that viral infection by these herpesviruses is not a major factor in EGGD, guiding veterinarians and researchers to focus on other causes and treatments.

Implications for Veterinary Medicine

• This study suggests that testing for EHV-2 and EHV-5 in horses with EGGD may not be clinically useful.
• Efforts to treat or prevent EGGD should likely focus on managing inflammation and protecting the glandular mucosa rather than targeting herpesviral infections.
• Future research may explore other infectious agents, environmental, dietary, or physiological factors involved in EGGD pathophysiology.