Feline infectious upper respiratory disease, otherwise known colloquially as “cat flu”, is frequently seen in unvaccinated cats and kittens, especially when kept in large groups. Animals from a multi-cat household, breeding groups, rescue shelters and strays are particularly at risk. Over 80% is caused by feline calicivirus and/or feline herpesvirus. Other pathogens could include bacteria such as Bordetella Bronchoseptica, Mycoplasma, Streptococcus, Pasteurella and so on. Often, factors such as poor ventilation, stress, high humidity, dusty environment, overcrowding and poor hygiene can predispose to this debilitating disease.

How does it spread?

Most infections are transmitted by aerosol and/or direct contact. Even if a cat recovers from a bout of cat flu, they then become latently infected carriers and the virus can reactivate at any time. An episode of stress such as boarding, medication (e.g. corticosteroids), re-homing etc can trigger the virus. Some cats, especially those affected by feline calicivirus, can continuously shed virus particles life-long and will be a constant source of infection for other cats.

Clinical signs

Clinical signs are varied, may depend on the specific causative pathogen, and are more commonly seen in younger cats. Affected cats are usually depressed and have a severe fever. Feline herpesvirus replicates in the epithelial cells of the nasal cavity, tonsils, conjunctiva and trachea, causing local necrosis of mucosa. Discharge from the nose, mouth and eyes are very common. Ocular infection can cause conjunctivitis, keratitis and corneal ulceration. Sneezing can also occur. Secondary bacterial infections are a common complication. Feline calicivirus targets similar cells but often also causes ulceration of the tongue, hard and soft palate, pharynx and nostrils. Such oral ulceration leads to salivation and anorexia. Coughing and difficulty breathing are seen less commonly but are still possible. Other clinical signs can also include skin ulceration, on the face or limbs, and abortions.

Diagnosis

Presumptive diagnosis is made with typical clinical signs and a history of exposure. Nasal or oropharyngeal swabs can be collected for culture or polymerase chain reaction tests (PCR) at the laboratory to isolate the specific pathogen. However, because some viruses can come and go, and are only intermittently shed (especially feline herpesvirus), this means that a cat may have no clinical signs of disease for a time but may still carry the virus. Laboratory results must therefore be interpreted with caution. It is also possible that the initial disease may have been eliminated, leaving a damaged nasal cavity that is then readily colonized by bacteria. So a cat might have a positive bacterial culture and will need to be treated for bacterial disease but may still be a cat flu carrier!

Sometimes, further investigation is still required to exclude other causes of disease – tests may include full blood and urine tests, radiographs of the nasal cavity, frontal sinuses and chest, as well as rhinoscopy and collection of tissue samples for histopathology.

Treatment

Unfortunately, there is no specific “cure” for this disease. Often, cat flu is an ongoing life-long condition and as stated previously, will flare up in cats that are stressed. When these episodes happen, symptomatic treatment and good nursing care is required. Treatment can include but is not limited to:

• Antibiotics are necessary for secondary bacterial infections and for specific bacterial pathogens such as bordetella bronchiseptica or mycoplasma. These are often given as tablets into the mouth for 2 – 3 weeks. If there is an ocular infection, then an antibacterial ointment may also need to be applied into the eyes.
• Nutritional and fluid support may be required depending on how severely ill or dehydrated your cat is. This might mean hospitalisation and rehydration via a drip. Appetite stimulants are an option for cats that will not eat. In more severe cases, feeding tubes may even be necessary.
• Mucolytics may help to remove build up of mucus and secretions, and therefore ease respiratory congestion.
• Anti-viral medication – there are a wide variety of anti-virals for feline herpesvirus, all of which have variable efficacy. L-lysine, famciclovir and interferon are just some of the options. Interferon, in particular, has also been suggested to act as a non-specific immune stimulant.

How else can I manage my cat at home?

We recommend regularly wiping away infected discharge from the eyes, mouth, and nasal cavity with saline. Please also consider isolating your cat from other cats at home or keeping him or her inside to avoid spread of infection. Nebulisation can also help to clear airways – one way of doing this is to keep your cat in your bathroom for a small period of time and allowing the steam from a hot shower to be inhaled.

Vaccination

Prevention is always better than cure, and at Thornleigh Vet, we therefore recommend vaccination for all kittens at 6-8 weeks, followed by monthly boosters until they are over 16 weeks old. The vaccine we use is called an “F3” and protects against feline herpesvirus, feline calicivirus and feline parvovirus, the first two of which, as mentioned above, are the main organisms responsible for cat flu. This is then followed by annual boosters. Please speak to one of our vets regarding a vaccination schedule suitable for your cat.