These are two different viruses which are often grouped as ‘cat flu’ because together they cause the majority of upper respiratory tract infections in cats.
They are both contagious and usually transmitted by direct or close contact between cats such as in sneezed droplets or discharge from the eyes; they may also survive for short periods in the environment and so could be transmitted via shared food bowls and litter trays, bedding or grooming aids.
Cat flu signs include sneezing, nasal and eye discharge, conjunctivitis, and mouth ulcers. Clinical signs vary from mild to extremely severe, and occasionally other complications may develop such as pneumonia. With FHV, a bit like cold sores in people, even after the initial signs subside, most cats will remain permanently infected and some will develop flare ups later on especially when their immune system is low.
Treatment for cat flu is based around treating the secondary bacterial infections with antibiotics. Affected cats commonly require supportive treatment as well such as a drip, steam inhalation and nutritional support.
In addition to cat flu, FHV can cause skin and eye problems (keratitis) and FCV can cause painful joints and chronic gingivitis and stomatitis (inflammation of the inside of the mouth). For these signs other treatments might be recommended such as antiviral medication or pain relief.
Both of these viruses are extremely common in our cat population and the disease can be severe which is why vaccination is considered important for all cats. Although vaccination does not always prevent infection with these viruses, it will help greatly in reducing the severity of disease.