Calicivirus Infection in Cats

Feline Calicivirus (FCV) is a common, highly contagious virus that causes respiratory infection and oral disease in cats.

• FCV is not usually life threatening, although in rare cases it develops into FCV-VSD which has more severe symptoms and is potentially fatal
• Symptoms of mild to moderate FCV include sneezing, runny eyes and nose, coughing, oral ulcers, and fever
• Cats with FCV-VSD also show swelling of the head and legs, jaundice, and bloody stool
• Diagnostic tools include physical examination and in some cases bloodwork, mucus cultures, or X-rays
• FCV runs its course in 10 days to 6 weeks
• Vaccination keeps symptoms mild although does not entirely prevent infection
• The prognosis in most cases is good
• Cats that develop FCV-VSD have a more guarded prognosis

Feline calicivirus is a viral infection that typically replicates in the lining of the upper respiratory system. The virus mutates rapidly, which leads to new strains emerging often.

Most cats who receive basic medical care are vaccinated against calicivirus as one of the core vaccines. Vaccination does not eliminate the possibility of FCV infection, but it typically ensures that only mild to moderate symptoms develop when infection does occur.

In rare cases, FCV develops into the more serious condition called FCV-VSD (feline calicivirus virulent systemic disease) which is fatal in more than half of cases.

Cats with the symptoms of FCV benefit from veterinary attention to confirm the underlying cause and develop a supportive treatment plan. Cats with the symptoms of FCV-VSD require prompt veterinary care.

In some cases, particularly in young kittens, elderly cats, and cats that have not been vaccinated, the virus overwhelms the immune system, leading to a more severe and life-threatening condition called FCV-VSD (feline calicivirus virulent systemic disease).

Feline calicivirus is a very common cause of upper respiratory infection in cats. It mutates rapidly and is extremely contagious. Cats that live in close contact with other cats, particularly in breeding houses, shelters, cat colonies, and pet stores are at greater risk of contracting and transmitting FCV to other cats.

FCV is highly contagious. It is transmitted through direct contact with an infected cat, through contact with objects that have been contaminated by an infected cat, and through particles in the air released by an infected cat sneezing. In some cases, humans who touch an infected cat transmit the virus to a healthy cat.

The virus is hardy and survives on surfaces for up to a month. It also remains in the body of some recovered cats for months or even years, meaning they can spread the virus long after their symptoms have disappeared.

Diagnosis of FCV centers around a physical examination to identify symptoms. There is often no need to confirm the specific cause of symptoms as there is no cure for FCV or the other potential causes of upper respiratory tract infections.

In some cases, particularly those not responding well to treatment and those with severe symptoms additional diagnostics to investigate further and guide treatment include:

• Bloodwork
• Analysis of nasal secretions
• X-rays
• Transtracheal wash (using fluid to sample cells within the lungs)
• Specialized testing to identify the virus directly

In some cases, cats are anesthetized in order to perform these tests.

Usually, the illness runs its course in 2 or 3 weeks. Supportive therapies may be helpful while the immune system clears the infection. Supportive therapies include:

• Eye medications
• Broad spectrum antibiotics
• Anti-inflammatory medications
• Environmental humidification
• Keeping face clean of eye and nose secretions
• Saline nose drops
• Provision of slightly warmed, palatable, soft foods to encourage eating
• Appetite stimulants

In cases where symptoms are severe and have not responded to treatment, hospitalization is sometimes necessary.

Once a cat has been exposed to the calicivirus, it typically takes 2 to 6 days before the onset of symptoms. Symptoms usually clear within 2 or 3 weeks. The cat is contagious during this whole period.

Generally, the symptoms of FCV are mild to moderate and resolve on their own. Most cases resolve within 10 days, however symptoms may last up to 6 weeks in some cases.

Certain cats remain contagious after the symptoms have cleared. In some cases, they continue to shed the virus for a few months. In rare cases, the cat is contagious for the rest of its life, despite having no further symptoms.

The prognosis for cats with mild to moderate FCV is good. FCV-VSD is fatal in more than half of cases.

Vaccination, though not effective in entirely preventing infection, is highly recommended to prevent severe symptoms.

Prevention requires avoiding contact with infected cats. Cats kept inside, away from other cats have a very low risk of FCV.

It is very difficult to prevent infection between in-contact cats because individuals can be contagious without showing symptoms.

Possible strategies include:

• Quarantining infected cats
• Disinfecting objects that have had contact with infected cats
• Washing hands between handling the infected cat and handling healthy cats

Cats adopted from shelters, breeding houses, cat colonies, or pet stores are very likely to be infected with FCV. Isolation from other cats in the house for at least 2 weeks to see if symptoms develop is recommended.

FCV is very common in cats. FCV-VSD is rare.

• Benign neglect
• Supportive care