Feline herpesvirus, also called feline viral rhinotracheitis, is one of the two main causes of cat flu. It is extremely common: a large proportion of cats have been infected at some point.

The defining feature

Cats do not clear this virus. After the first infection it remains dormant in the nerve tissue for life and reactivates at times of stress.

This explains a pattern owners describe often: a cat that “catches a cold” every time something changes. A house move, a new animal, boarding, an operation, another illness. It is not a new infection each time; it is the same virus waking up.

What it looks like

Sneezing, discharge from the nose and eyes, red inflamed eyes, fever, lethargy and reduced appetite.

Herpesvirus attacks the eye in particular. It causes conjunctivitis, and it can cause corneal ulcers, which are painful and can threaten sight. A cat holding one eye shut, or with a cloudy or hazy cornea, needs to be seen promptly rather than watched.

In kittens, severe early infection can scar the tear ducts and nasal passages permanently, leaving an adult cat with a lifelong runny nose and recurring infections. This is the snuffly cat owners describe as never quite getting over it.

Why appetite matters

A blocked nose removes the sense of smell, and a cat that cannot smell will not eat. Since cats that go without food for more than a couple of days risk hepatic lipidosis, keeping food going is a central part of treatment rather than an afterthought.

Treatment

Supportive care is the basis: cleaning the eyes and nose, warmed strongly scented food, fluids where needed, and a humid environment.

Antiviral eye treatment is used where the cornea is involved. Lysine supplementation has been widely used, though the evidence for it is weak. Antibiotics are given only for secondary bacterial infection, since they do nothing against a virus.

Most episodes settle within one to two weeks.

Managing a cat that keeps flaring

Since stress drives recurrence, management is mostly about reducing it:

Keep routine, feeding times and litter arrangements stable
Introduce new animals slowly
Provide hiding places and high perches
Plan ahead for boarding and house moves
Treat any other illness promptly, since illness itself is a trigger

Vaccination

Herpesvirus is part of the core vaccine. Vaccination does not prevent infection or eliminate the carrier state, but it reduces the severity of disease significantly, and that is worth having.

When to come in

An eye held shut, a cloudy cornea, or discharge that has turned thick and coloured. A cat that has stopped eating. Any change in breathing. Or a kitten, where the risk of permanent damage is highest.