Feline calicivirus (FCV) is a virus that infects domestic cats, causing a range of flu-like symptoms. There are many strains of FCV with varying ability to infect cats and varying severity of disease. The virus is able to mutate/change over time (similar to human flu virus) which is why cats that have recovered from calicivirus or are vaccinated may still get mild symptoms if they are re-infected with a new strain.
Calicivirus may enter the cat’s body via the eyes, nose or mouth. This can occur through direct contact with an infected cat or through a contaminated environment. Possible environmental sources include floors, bedding, food and water bowls, litter trays and people's hands/clothing. Calicivirus can survive for up to one week on areas/objects with which an infected cat has had contact.
As there are different strains of FCV, different signs may be seen. The most common signs include fever, ulcers on the mouth and tongue, sneezing and mild conjunctivitis. Infected cats may be depressed/lethargic and may have discharge from the eyes and nose. If mouth ulcers are present there may be excessive salivation/wetness around the mouth. Infected cats may be unwilling to eat. Some less common signs include difficulty breathing or lameness/limping. Calicivirus can also be involved in ongoing cases of oral ulceration (known as chronic stomatitis/gingivitis).
It is not always essential to diagnose the exact agent involved in individual cats with flu symptoms. However in some circumstances diagnostic tests may be advised. For example: in colonies of cats with flu signs (such as breeding colonies and shelters); in vaccinated cats that become ill; and cats with recurrent or ongoing signs such as ongoing ulceration of the mouth.
Calicivirus may be suspected based on clinical signs alone. It may be diagnosed by taking a swab from the back of the cat’s throat (oropharyngeal swab) and/or from the inside of the eyelid (conjunctival swab). The swab is placed in a special viral transport medium and sent to a laboratory in order to isolate and grow the virus.
The test results must be carefully interpreted by the veterinarian along with other information. False positive results may occur – where the virus is present but is not actually causing disease. False negative results may also occur – where the virus is present at a low level and is not detected by the test.
At present there are no specific antiviral drugs available for use in cases of feline calicivirus. Treatment of calicivirus is generally symptomatic and aimed at supporting the cat whilst its immune system fights off the virus. Treatment may include antibiotics (to treat or prevent secondary bacterial infection), decongestants/steam therapy (to break down thick mucus in the nasal passages), anti-inflammatories (to reduce fever and give pain relief from oral ulcers) and sometimes fluid therapy (if the cat is dehydrated and unable to eat).
Some cases may benefit from the use of Interferon. Interferons are proteins produced by the body in response to viral infection. Medicinal versions of these are available however their effectiveness against calicivirus is unproven at present.
After infection with FCV most cats will shed the virus in secretions from the eyes, nose and mouth for at least 30 days. After this, many cats will eliminate the virus completely. However cats can enter a ‘carrier’ state, where they appear clinically well but continue to shed the virus continuously and act as a potential source of infection for other cats.
After the initial 30 days, the proportion of cats still shedding virus gradually declines. Studies have shown that around 50% of infected cats will still be shedding virus at 75 days. This proportion becomes less as time goes on. This means that the longer it has been since the cat was infected/ill, the more likely it is that they will have eliminated the virus and will not be a carrier. However, a small number of cats will become lifelong carriers and continue to shed the virus indefinitely.
It is impossible to predict how long an individual cat will remain infective. Additionally – cats that have fully recovered can be re-infected with the virus and start shedding again. This is why it is very difficult to eradicate FCV completely from a group of cats.
There are a number of measures you can take to reduce the likelihood of calicivirus infection in your cat:
The most important of these is ensuring that vaccination against the disease remains up to date at all times. Kitten vaccinations should begin at 9 weeks of age with a full course (usually 2 or 3 injections depending on the vaccine product used and age at which vaccination is started). All cats should receive an annual booster vaccination thereafter. You may also consider additional vaccine boosters if your cat is entering a high risk environment (such as a boarding cattery or cat show).
- Wherever possible, try to ensure your cat is not stressed and has minimal contact with other cats.
- Keep food and water bowls securely indoors where other cats do not have access to them.
- Observe good hygiene if you have come into contact with another cat outside the house – wash your hands thoroughly before interacting with your own cat.
- If introducing a new cat to the household – ideally look for a cat without any history of respiratory disease.
- If there is concern that the cat may be a carrier of calicivirus it should remain isolated for a minimum of 30 days and ideally viral testing should be performed at weekly intervals. If the tests are consistently negative during this time the risk of introducing calicivirus when the cats meet should be low.
Management and hygiene are very important in shelters, catteries and colonies due to the large number of cats in close proximity:
- All cats should be fully vaccinated before entering the group.
- New additions to a disease free group should be isolated and tested as outlined above.
- All cats should ideally be housed individually with sufficient space between them and solid partitions to prevent direct contact.
- Enclosures should be side by side rather than facing one another to prevent virus transmission via sneezing.
- All enclosures should be thoroughly disinfected between residents.
- Hands and shoes should be disinfected between entering each enclosure and each enclosure should be attended to fully before moving on to the next.
- Food bowls, water bowls and litter trays should be cleaned and soaked in disinfectant daily. Ideally have two sets of these so that each set can be rested for 24 hours after disinfection before being used again.
- Any cats with respiratory signs, history of calicivirus infection or those suspected of being carriers should be isolated and attended to last each day. This reduces the likelihood of transmitting disease to uninfected cats.
If you suspect that there is a calicivirus problem within your cat population, seek veterinary advice on the best action to take. Advice may vary depending on the individual situation and any plans to eradicate disease are likely to work best if tailored to your specific needs.