In cats, however, the disease commonly is caused by feline herpesvirus Type - 1 and, because of that, often emerges during times of stress. (morrisanimalfoundation.org)
Feline Viral Rhinotracheitis is a highly contagious disease caused by Feline Herpesvirus Type 1 (FHV - 1) and is one of the most common causes of upper respiratory infections in cats. (rachelebaker.com)
(ref) Adult cats commonly develop these ulcers due to infection with feline herpesvirus - 1. (2ndchance.info)