Moderate severity
Feline Calicivirus
A highly contagious virus and one of the main causes of "cat flu". It typically brings sneezing, a runny nose and — distinctively — painful ulcers on the tongue and mouth.
⚠️ Common symptoms
Feline calicivirus is, alongside feline herpesvirus, one of the two viruses behind the familiar bundle of symptoms owners call "cat flu". It is remarkably common and remarkably contagious, circulating wherever cats live in groups — shelters, catteries, breeding colonies and multi-cat homes. Most cats meet it at some point, and while it is rarely life-threatening in healthy adults, it can make a cat thoroughly miserable.
The symptom that most distinguishes calicivirus from other respiratory bugs is the mouth ulcer. The virus has a particular fondness for the tissues of the tongue and mouth, raising painful sores that leave a cat drooling and unwilling to eat. Combined with the sneezing, runny nose and watery eyes typical of cat flu, the result is a sneezing, dribbling, off-colour cat that needs gentle nursing. Some strains also cause a curious, temporary "limping syndrome", in which young cats develop transient lameness as the virus inflames their joints.
There is no antiviral that cures it, so care is supportive: keeping the cat eating and hydrated, easing the pain of the ulcers, and watching for secondary bacterial infections that may need antibiotics. Warmed, strongly-smelling food helps tempt a congested cat whose sense of smell — and therefore appetite — has dulled. The great majority recover within a couple of weeks, although a significant minority become carriers, harbouring and shedding the virus long after they look well, which is how the infection quietly perpetuates itself in a population.
Vaccination is the best defence. Calicivirus is included in the core vaccine given to all kittens and boosted through life. Because the virus mutates and many strains exist, the jab cannot guarantee a cat will never catch it — but it dramatically blunts the severity, turning what could be a debilitating illness into a mild sniffle. In group-living situations, scrupulous hygiene and the use of effective disinfectants are the other half of the equation, since this is one virus that lingers stubbornly in the environment.
🔍 Causes
Feline calicivirus (FCV) spreads through saliva, and nasal and eye secretions — by direct cat-to-cat contact, shared bowls and bedding, or human hands. It is extremely hardy in the environment and resistant to many disinfectants, so it spreads readily in multi-cat homes, shelters and catteries. A few rare strains cause a severe, sometimes fatal whole-body form known as virulent systemic FCV.
🛡 Prevention
Vaccination is the cornerstone — FCV is part of the core "flu and enteritis" combination vaccine every cat should receive as a kitten and keep boosted. The vaccine does not always prevent infection outright but greatly reduces the severity of illness. In multi-cat settings, isolating sick cats, using bleach-based disinfectants, and good hygiene between handling cats limit spread.
💊 Treatment
There is no drug that kills the virus, so treatment is supportive while the cat's immune system clears it. This means pain relief for mouth ulcers, soft and strongly-scented food to tempt a sore, stuffy cat to eat, fluids to prevent dehydration, and antibiotics only if a secondary bacterial infection sets in. Most otherwise-healthy cats recover within one to three weeks, though some become long-term carriers that shed the virus intermittently.
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⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.