Cat flu is the common name given to infectious upper respiratory disease in cats. There are actually several infectious agents that can be involved, but they all create largely the same clinical signs: sneezing and nasal discharge, and conjunctivitis with runny, painful eyes.
The most common infectious agents involved in ‘cat flu’ are feline herpesvirus and feline calicivirus. It can be almost impossible to tell which is the cause based on clinical signs alone. Some health problems are more often associated with one virus than the other: for example, herpesvirus often causes ulcers on the clear surface of the eye (cornea), whereas calicivirus is more likely to cause ulcers in the mouth. But usually we have to send a sample to the lab to know which virus is involved.
Cats are infected by coming into contact with respiratory droplets from an infected cat. The viruses can survive in the environment fairly well. This means infection may be carried on objects without direct contact between cats.
Initially affected cats are pyrexic (feverish) though this has often resolved by the time other signs are evident. They will have a discharge from the nostrils and the eyes. Initially this is clear, but it becomes thick and yellow over time. Often affected cats will be off their food.
Clinical signs can be present for anything from a week, up to six weeks.
In most cats, cat flu isn’t a dangerous illness. It certainly makes them miserable when clinically affected, and as with most illnesses very young kittens or elderly cats are at risk of becoming seriously unwell, often with a secondary bacterial infection. But it is very rarely fatal and most cats will recover uneventfully with some supportive care.
However, particularly in the case of feline herpesvirus, persistent infection is very common. This means that the cat’s immune system is not able to clear the virus from its body. Herpesvirus tends to hide away in the nerves, and reactivates at times of stress. This means infected cats will often suffer with chronic relapses of respiratory disease and particularly conjunctivitis and eye ulceration for the rest of their life.
Chronic infection with calicivirus is also associated with a condition known as feline gingival stomatitis complex, though the exact combination of factors involved is not fully understood.
Infection of young kittens with either virus can lead to permanent damage to the delicate scrolled bones inside the nose (nasal turbinates) which may lead to chronic respiratory infection.
We recommend vaccination to prevent cat flu in all kittens, especially given the possibility for chronic health problems as a result of infection. Vaccinations should be administered from 9 weeks of age, and kittens should receive 2 doses 3-4 weeks apart. Vaccines against cat flu include innoculation against panleukopaenia virus, and the vaccination against feline leukaemia virus can be combined with it.
Preventing the spread of feline herpesvirus is particularly difficult, due to the chronic nature of the disease, and intermittent shedding. If a queen is a carrier of FHV, it often reactivates with the stress of pregnancy and birth. This means she is shedding virus which can infect the kittens just when they are most vulnerable. If your cat may be infected with feline herpesvirus, we would strongly advise against using them for breeding.