A clear, step by step guide to treating Feline Calicivirus in cats.
Feline Calicivirus (FCV) is one of the most common and most contagious causes of cat flu, bringing sneezing, painful mouth ulcers and fever. Most cats do well with early treatment and good supportive care. This guide walks you through recognising, diagnosing and treating Feline Calicivirus (FCV), and caring for your cat afterwards.
Four parts, from the first signs to recovery.
Everything you need to understand Feline Calicivirus (FCV) and the treatment that targets it, set out in the order you will need it.
- 1
Recognise the symptoms
The oral, respiratory and severe forms of Feline Calicivirus (FCV), and what each one looks like.
- 2
Confirm the diagnosis
The tests vets use to separate Feline Calicivirus (FCV) from other causes of cat flu.
- 3
Start treatment
CaliciX and CaliciX Max, plus the supportive care that goes alongside them.
- 4
Care and prevention
Isolation, feeding a sore mouth, vaccination and long term monitoring.
What is Feline Calicivirus in cats?
Feline Calicivirus (FCV) is a highly contagious virus that causes upper respiratory infection and painful mouth ulcers in cats. It spreads through saliva, nasal and eye discharge, and through shared bowls and bedding, so it moves quickly through multi cat homes, catteries and shelters. Most cases are mild to moderate, but early care helps prevent complications.
- 1
Acute Feline Calicivirus
The most common form. Sneezing, nasal discharge, fever and painful ulcers on the tongue and gums. Most cats come through it with supportive care over a few weeks.
- 2
Chronic Feline Calicivirus
Some cats develop long term gum and mouth inflammation, known as Feline Chronic Gingivostomatitis (FCGS), or become carriers that keep shedding the virus. These cats need ongoing dental and supportive care.
A rare but severe form called Virulent Systemic Feline Calicivirus (VS-FCV) can cause high fever, swelling of the face and limbs, and organ involvement. It is a veterinary emergency and needs urgent care.
Recognising symptoms of Feline Calicivirus
Feline Calicivirus (FCV) mainly affects the mouth and the upper airways. Mouth ulcers and drooling are the most telling signs. Watch for these.
- 1Sneezing
- 2Nasal discharge
- 3Mouth and tongue ulcers
- 4Drooling
- 5Fever
- 6Lethargy
- 7Loss of appetite
- 8Eye discharge
- 9Lameness or limping
- 10Difficulty eating
Diagnosing Feline Calicivirus in cats
Feline Calicivirus (FCV) shares symptoms with other cat flu viruses, so vets combine the clinical picture with laboratory confirmation. These are the tests used most often.
- 1
Clinical and oral exam
Mouth ulcers together with respiratory signs are a strong indicator of Feline Calicivirus (FCV).
- 2
RT-PCR swab
An oral or oropharyngeal swab confirms the virus is present.
- 3
Virus isolation
Culture from a swab identifies the calicivirus in more complex cases.
- 4
Differential testing
Rules out Feline Herpesvirus (FHV-1) and any secondary bacterial infection.
Treating Feline Calicivirus in cats
Feline Calicivirus (FCV) is not removed by a single medication, but early treatment gives the best outcome. Care combines a targeted antiviral with pain relief, hydration and nutrition while the immune system does its work.
CaliciX and CaliciX Max.
CaliciX and CaliciX Max are oral antiviral capsules for Feline Calicivirus (FCV) and Feline Chronic Gingivostomatitis (FCGS), built on EIDD-1931, the active antiviral form of molnupiravir. Both work best when started early.
- EIDD-1931 itself, not human molnupiravir tablets divided down.
- Given alongside pain relief for mouth ulcers, plus fluids and soft, palatable food.
- Treatment length is set by your veterinarian, based on how your cat responds.
- 1
CaliciX, 15 mg
The standard strength, for most cats with oral disease caused by Feline Calicivirus (FCV). Size 3 capsules that can be given whole or mixed through food.
- 2
CaliciX Max, 30 mg
The high strength option, for severe, refractory or high viral load disease, cats that have not responded to standard therapy, and larger cats. Also used where Feline Chronic Gingivostomatitis (FCGS) has not settled after dental extractions.
Not for pregnant or nursing queens. EIDD-1931 has potential teratogenic effects, so neither strength should be given to pregnant or nursing cats, or to cats being bred. Tell your veterinarian about every medication your cat is receiving before starting.
Care, prevention and recovery
Because Feline Calicivirus (FCV) spreads so easily, good hygiene and gentle daily care make a real difference. Focus on these four areas.
- 1
Isolation and hygiene
Feline Calicivirus (FCV) is highly contagious between cats. Separate the sick cat, wash your hands, and clean bowls and bedding with a bleach based product, because the virus resists many ordinary disinfectants.
- 2
Nutrition
Offer soft, warm, strong smelling food to tempt a sore mouth and a blocked nose. Keep fresh water available, since cats with Feline Calicivirus (FCV) dehydrate quickly.
- 3
Vaccination and prevention
Keep core vaccines up to date. Vaccination reduces the severity of Feline Calicivirus (FCV), though it cannot prevent every strain. Limit contact with unknown cats.
- 4
Comfort and monitoring
Gently wipe away eye and nose discharge, keep your cat warm, and watch for worsening breathing, facial swelling, or a refusal to eat.
Good to know: Feline Calicivirus (FCV) spreads easily between cats, so isolation matters. It does not infect humans, dogs, or other non feline pets.
Common questions about Feline Calicivirus
What should I feed a cat with Feline Calicivirus?+
Soft, warm, strong smelling food is easiest for a sore mouth and a blocked nose. Warming food gently lifts its aroma and encourages eating. Keep fresh water available at all times.
How long does treatment take?+
That depends on how severe the disease is and how early treatment starts, so the length of the course is set by your veterinarian rather than fixed in advance. Some cats keep shedding the virus for a while even after their symptoms clear.
What is the difference between CaliciX and CaliciX Max?+
The active ingredient is the same, EIDD-1931. CaliciX carries 15 mg per capsule and CaliciX Max carries 30 mg. The higher strength is used for severe or refractory disease, for cats that have not responded to standard therapy, and for larger cats.
Is Feline Calicivirus contagious to other cats?+
Yes. Feline Calicivirus (FCV) passes easily between cats through saliva, nasal and eye discharge, and shared items. Isolate the sick cat and clean shared surfaces.
Can Feline Calicivirus spread to humans or dogs?+
No. Feline Calicivirus (FCV) infects cats only. It does not spread to humans, dogs, or other non feline pets.
Does the vaccine prevent Feline Calicivirus?+
Vaccination reduces the severity of illness and is strongly recommended, but because Feline Calicivirus (FCV) has many strains it cannot guarantee full protection. Keeping vaccines current still helps a great deal.
What is Virulent Systemic Feline Calicivirus?+
VS-FCV is a rare but severe form that causes high fever, swelling of the face and limbs, and organ involvement. It can be life threatening and needs urgent veterinary care.
Do cats stay carriers after they recover?+
Some cats keep shedding Feline Calicivirus (FCV) for weeks or months after recovering, and a small number carry it long term. These cats can still infect others, so ongoing hygiene matters.
More questions are answered in the CureFIP FAQ.
Think your cat may have Feline Calicivirus?
If your cat has mouth ulcers, sneezing or a fever, act early, when treatment works best. Browse the available Feline Calicivirus (FCV) treatments to get started.
This page is for general educational purposes and does not replace veterinary advice. Always consult a qualified veterinarian for diagnosis and a treatment plan tailored to your cat.