Feline Herpesvirus-1 is what causes Viral Rhinotracheitis (FVR), a very common upper respiratory pathogen. Symptoms include sneezing, runny nose and eyes, fever, anorexia and depression. Conjunctivitis can also occur, and can become quite severe. This can lead to corneal ulcers, often called dendritic ulcers due to their appearance (branching appearance).
Most cats become infected with this virus as kittens, through either direct contact or contact with a fomite (an inanimate object or substance, such as clothing, furniture, or soap) carrying the disease.This virus targets the epithelia of the upper respiratory tract and conjunctiva, and can lead to inflammation, ulceration and necrosis of these cells. In severe/untreated cases, erosion of the nasal bones can occur, leading to chronic “snufflers.”
Like in people, herpes is forever in cats. The virus often becomes latent and hides out in the nervous system until the cat becomes stressed. Signs may be present or absent, but transmission to other cats is possible at this time. While the vaccine does not prevent infection, it can prevent the disease state, and it is considered part of a core vaccine series for cats.
Source: "The Cat" by Susan E. Little.