Detailed explanation of Feline Calicivirus (FCV), a major cause of upper respiratory disease in cats, covering symptoms, transmission routes, treatment methods, and vaccination. Also covers precautions for multi-cat households with chronically infected cats.
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Detailed explanation of Feline Calicivirus (FCV), a major cause of upper respiratory disease in cats, covering symptoms, transmission routes, treatment methods, and vaccination. Also covers precautions for multi-cat households with chronically infected cats.
Feline Calicivirus (FCV)
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Feline Calicivirus (FCV) is one of the primary causative viruses of upper respiratory disease in cats (commonly referred to as "cat flu"). Alongside Feline Herpesvirus 1 (FHV-1), it is among the most common viruses causing respiratory disease in cats.
While often dismissed as a routine cat cold, calicivirus has a distinctive symptom: oral ulcers and mouth sores. In severe cases, it can develop into chronic stomatitis, causing lifelong pain to the affected cat. This disease requires special attention in multi-cat breeding environments and multi-cat households.
Characteristic Symptoms
FCV symptoms vary depending on the pathogenicity of the infected strain and individual variation.
Typical symptoms
The most distinctive feature is ulcer formation in the mouth, nasal cavity, and footpads. Round ulcers (aphthous ulcers) develop on the gums, tongue, or inside the mouth, causing pain, decreased appetite, and excessive drooling. This is a key difference from FHV-1 and an important indicator to suspect FCV.
Additionally, sneezing, nasal discharge, and conjunctivitis and other upper respiratory symptoms appear. Elevated body temperature (fever), lethargy, and loss of appetite are also common.
Progression from mild to moderate
In healthy adult cats with normal immune function, typical cat flu symptoms usually resolve spontaneously within 1–2 weeks. However, many cats infected with this virus continue to shed the virus (become carriers) for extended periods.
Severe complications
In some strains (virulent strains), systemic inflammatory reactions occur, leading to skin edema, necrosis, and multi-organ failure, resulting in a severe condition called Virulent Systemic FCV (VS-FCV). Even adult cats show high mortality rates, so emergency intervention is necessary if an outbreak occurs.
Association with chronic stomatitis (FCGS)
FCV is thought to be involved in the onset and worsening of Feline Chronic Gingivostomatitis (FCGS) in cats. If there is persistent inflammation in the oral cavity with poor response to antibiotics or anti-inflammatory pain relievers, FCV involvement should be suspected.
Transmission Routes and Contagiousness
FCV is highly contagious and spreads through the following routes.
Direct and indirect contact
The nasal secretions, saliva, eye discharge, and feces of infected cats contain large amounts of virus. In addition to direct contact, indirect infection through shared food bowls, water dishes, litter boxes, and toys is common.
Droplet transmission
Droplets from sneezing can travel more than 2 meters, creating a risk of infection to other cats in the same room.
Long-term shedding from carrier cats
After infection, FCV carrier cats may continue to shed the virus for months or, in some cases, for the cat's entire lifetime. Asymptomatic cats can become sources of infection, which is not uncommon. For this reason, once introduced into a multi-cat environment, the virus becomes difficult to eliminate.
Diagnostic Methods
FCV diagnosis is primarily made through PCR testing (genetic testing) or viral isolation testing. Samples are collected from oral or pharyngeal swabs, or conjunctival swabs and sent to an external testing facility through an animal hospital.
Since symptoms alone make it difficult to distinguish FCV from FHV-1, the presence or absence of oral ulcers is an important differential point (ulcers are characteristic of FCV; FHV-1 tends to present with stronger eye symptoms). Definitive diagnosis requires testing.
Treatment
Currently, no broadly available antiviral drugs specific to FCV have been developed. Treatment is primarily based on supportive care.
Symptomatic treatment according to symptoms
If appetite loss continues, forced feeding or appetite stimulants are used. Dehydration is treated with intravenous fluids. Antibiotic administration to prevent secondary bacterial infection is also standard treatment. Pain relief medications are used for oral ulcer pain.
Management of chronic stomatitis
If FCGS develops, long-term medical management is necessary. Interferon therapy, immunosuppressive therapy, or tooth extraction (full premolar and molar extraction or full-mouth extraction) may be considered. While tooth extraction may seem extreme, it is an effective established treatment for chronic stomatitis.
Vaccination and Prevention
FCV has a core vaccine available (vaccines recommended for all cats as basic protection). In Japan, it is included in the feline triple vaccine (FHV-1, FCV, and panleukopenia).
Vaccine effectiveness and limitations
Vaccines do not completely prevent infection but significantly reduce the risk of disease development and severity. Since FCV is prone to mutation, vaccine effectiveness may be reduced when the vaccine strain differs from the circulating strain. However, the benefits of vaccination still outweigh the drawbacks.
Vaccination schedule
Kittens receive 2–3 initial doses starting at 8 weeks of age, given 3–4 weeks apart. Adult cats should continue booster vaccinations every 1–3 years under veterinary guidance.
Precautions for Multi-Cat and Breeder Environments
Multi-cat environments carry high risk of disease spread and require careful management.
Quarantine for new cats
Newly acquired cats (whether purchased or rescued) should be completely isolated from resident cats in a quarantine space and observed for at least 2 weeks. If no symptoms appear during this period, contact can gradually be increased.
Management of carrier cats
FCV carrier cats pose a risk of spreading infection. Particularly in environments with immunocompromised elderly cats, sick cats, or young kittens, contact with carrier cats should be limited as much as possible.
Sanitation management
Food bowls and water dishes should be provided individually for each cat, avoiding sharing. Since FCV can survive in the environment for 1–2 weeks, regular disinfection (wiping floors and equipment with hypochlorous acid-based bleach) is effective in preventing spread.
Summary
Feline Calicivirus (FCV) is a common disease in cats, but it should not be underestimated due to the risks of oral ulcers, chronic stomatitis, and virulent severe disease. Consistent vaccination, quarantine of new cats, and strict sanitation of equipment can significantly reduce infection risk. If symptoms are concerning, consult a veterinarian early to receive proper diagnosis and treatment.
