Equine gastric ulcer syndrome (EGUS) is an umbrella term for two separate conditions, equine squamous gastric ulcer syndrome (ESGUS) and equine glandular gastric ulcer syndrome (EGGUS). The pathogenesis of ESGUS is fairly well described by previous literature, however, the pathogenesis of EGGUS remains poorly understood. Peptic ulcers in the stomach of humans, which consists of glandular gastric mucosa only, have been associated with various herpesviruses, such as the alphaherpesviruses herpes simplex virus type 1 (HSV-1) and Varicella zoster virus (VZV) and the gammaherpesvirus Epstein Barr virus (EBV). We have previously demonstrated the presence of both equine gammaherpesvirus 2 (EHV-2) and 5 (EHV-5) in the gastric mucosa of healthy horses. To build on our previous work, the overarching hypothesis is that equine gammaherpesviruses are associated with EGUS, both equine squamous gastric ulcer syndrome (ESGUS) and glandular gastric ulcer syndrome (EGGUS). In this study, we aim to address following two specific hypotheses:

• Hypothesis 1 (H1): EHV-2 and -5 are more prevalent in horses with ulcers compared to horses with a normal stomach.
• Hypothesis 2 (H2): In horses with virus-positive ulcers, EHV-2 and -5 are present in an active state at the ulcer site but in a latent state at the normal site of the stomach.

In order to test this, we will collect gastric mucosa samples from horses at postmortem exam as well as clinical cases. The samples will include normal and ulcerated tissue from horses with grossly normal gastric mucosa, horses with ESGUS, horses with EGGUS, and horses with both ESGUS and EGGUS. They will be studied at a macroscopic, microscopic, and molecular level using gross necropsy or gastroscopy exam, in situ hybridization assay, and qPCR, respectively. [Should we find a link between these gammaherpesviruses and gastric ulcers in horses, then treatments, such as anti-virals could be successful in managing this syndrome.]