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Feline CaliciVirus (FCV) Infection

17th August 2018

Feline CaliciVirus (FCV) Infection

Feline calicivirus (FCV) is a highly contagious virus that is one of the major causes of upper respiratory infections (URIs) or cat flu in cats.

This virus is ubiquitous and causes disease in cats all over the world. See also Upper respiratory infections (URIs, Cat flu) in cats. Together, FCV and feline herpesvirus cause the vast majority of URIs in cats.

What is FCV and how is it spread?

Feline calicivirus (FCV) is a small virus that mainly causes acute upper respiratory infections (URIs) in cats, although it has been associated with some other diseases also (see below). The virus is readily transmitted between cats through:

  • Direct contact – through contact with saliva, ocular or nasal secretions
  • Inhalation of sneeze droplets
  • Sharing or food bowls and litter trays
  • A contaminated environment (including bedding and grooming aids) – FCV can potentially survive up to a month in the environment, although probably often does not survive more than 7-14 days.

A characteristic of FCV is that the virus mutates readily during replication and this means that many different strains of the virus exist in nature, some of which are more pathogenic than others (ie, are a cause of more severe disease).

What are the clinical signs of FCV infection

  • Acute upper respiratory infection – Acute URI is the most common manifestation of FCV infection. Typical signs include sneezing, nasal discharge, ocular discharge, conjunctivitis, ulceration of the tongue, lethargy, inappetence and fever. Signs may last from a few days to a few weeks and vary in severity. In young kittens the virus may also cause pneumonia.
  • Gingivitis and stomatitis – chronic gingivitis is a common disease in cats, although the underlying cause(s) are not fully understood. However, FCV can be isolated from virtually all cats with this condition, and it is thought that persistence of FCV infection in these cats is part of the cause of the gingivitis. This is not a simple disease though, as other cats exposed to the virus from a cat with chronic gingivitis will usually only develop upper respiratory signs. Other factors therefore seem to predispose individual cats to developing gingivitis in response to persistent FCV infection.
  • Limping syndrome – occasionally, in young cats in particular, infection with FCV may also cause joint inflammation (arthritis). This is a transient problem, usually only lasting a few days, but the kitten or cat may be extremely uncomfortable with painful joints during this time. Often, but not always, there will be signs of URI at the same time. (See: Limping syndrome and feline calicivirus)
  • Virulent systemic FCV infection – vsFCV – on rare occasions, outbreaks of disease have been reported with very much more pathogenic strains of FCV termed vsFCV. These are associated with mutations of the virus that allow infection to be established within different organs and in the cells that line blood vessels. This can result in severe disease including pneumonia, hepatitis (liver inflammation), pancreatitis, skin swelling and ulceration, and bleeding from the nose and intestine. Fortunately these outbreaks are very rare, but up to 50% or more of affected cats may die

How is FCV infection diagnosed?

In most cases, a specific diagnosis of FCV infection will not be required. The presence of typical signs of URI is enough for a presumptive diagnosis of FCV (and/or feline herpesvirus – FHV) infection. If a specific diagnosis is required, ocular or oral swabs can be submitted to a veterinary laboratory where the virus can be grown in culture or, more commonly, detected by PCR (a molecular technique for detecting the genetic material of the virus).

Treatment and management of FCV infections

FCV infections are frequently complicated by secondary bacterial infections, so supportive treatment with antibiotics is usually required. Good nursing care is critical and cats may need to be hospitalised for intravenous fluid therapy and nutritional support in severe cases. Steam inhalation or nebulisation may help in cases of severe nasal congestion and as the cat will not be able to smell food well, using tinned or sachet foods that are gently warmed will help.

In colonies of cats, any cat showing clinical signs should be isolated if at all possible, and strict hygiene should be ensured with disinfection, and use of separate feeding bowls, litter trays, implements etc, careful washing of hands, use of separate (or disposable) apron etc.

Vaccination against FCV

Vaccination for FCV is important for all cats. Two or three injections are recommended in kittens, starting at around 8 weeks of age. Cats should receive a booster at a year of age, and after that should receive further booster vaccines every 1-3 years.

Vaccination does not necessarily prevent infection with FCV but will greatly reduce the severity of clinical disease. Additionally, as there are many different strains of the virus, it is difficult to design a vaccine that will protect against all of them. Some newer vaccines incorporate more than one strain of FCV to provide a broader range of protection.

Limping syndrome and feline calicivirus

Feline calicivirus (FCV) is one of the major causes of feline infectious upper respiratory tract disease (cat flu).

Classical cat ‘flu’ follows a short incubation period of 3–5 days and consists predominantly of upper respiratory tract disease (sneezing, rhinitis, nasal discharge, conjunctivitis, ocular discharge and oral ulceration). These signs may be accompanied by pyrexia (raised temperature) and occasionally other manifestations, such as coughing and pneumonia.

From an early stage, transient lameness has also been observed as a clinical feature in some cats infected with FCV and it now seems clear that this is, in fact, a relatively common clinical manifestation of FCV infection. The transient lameness associated with FCV has acquired the name ‘limping syndrome’.

Limping syndrome is caused by FCV infection

FCV was confirmed as a cause of lameness during early observations that showed kittens infected with FCV from other cats with limping syndrome developed pyrexia, depression and inappetence within 2-3 days. Within hours of developing pyrexia, the kittens also developed generalised or localised stiffness, manifesting as shifting lameness in some, and an almost complete reluctance to move in others. None of the cats developed sneezing or ocular discharge, but about one third developed oral ulcers (one of the classic signs of FCV upper respiratory infection). Clinical signs were reported to resolve within 48 to 72 hours with no residual effects. The joints were painful on touch/manipulation, and generalised hyperaesthesia (pain or hypersensitivity to touch) was present.

FCV can affect the joints

Further studies of FCV infection showed that FCV viral proteins could be identified in the synovial membrane (the membrane surrounding the joint space) in several cats either vaccinated with a live FCV vaccines and/or infected with FCV. Evidence suggests that the viral proteins are present in association with antibodies, and thus may be present as ‘immune complexes’ (a combination of the viral protein and a specific antibody produced against it) which can provoke an inflammatory response. In some cases, the entire FCV virus can be isolated from joints of cats exposed to FCV showing signs of disease including lameness, with evidence that the virus was provoking an acute inflammatory reaction.

It is therefore evident that after natural exposure to FCV, systemic infection arises which can, at least in some circumstances, involve localisation of the virus to joint tissues where it may cause an inflammatory reaction, possibly through local replication there or possibly through stimulation of immune-mediated inflammation. This is a form of viral-induced polyarthritis (joint inflammation affecting more than one joint).

It seems that certain strains of FCV have a greater propensity to cause lameness than others.

FCV vaccination and the limping syndrome

Limping syndrome associated with FCV infection is most commonly seen in kittens, and may occur after their first vaccination. Some vaccines may be more likely than others to induce limping syndrome but as manufacturers change and refine their vaccines this appears to be less common now. Additionally, even when occurring after vaccination, some cases of limping syndrome may still be associated with acquired FCV infection rather than the vaccine itself.

Summary – the role of FCV in limping syndrome

In summary, FCV clearly has the ability to cause a transient polyarthritis (inflammation affecting more than one joint) in cats, and most commonly in young kittens. This is a fairly common manifestation of FCV infection and may occasionally also be associated with FCV vaccination (especially live vaccines).

The severity varies widely from inapparent inflammation and mild limping, through to severe polyarthritis where the cats are reluctant to move, inappetent and the joints appear painful when touched.

Affected cats spontaneously recover, but if clinical signs are severe, anti-inflammatory medication may be required and your kitten or cat should be checked by your vet. Although FCV is obviously a common cause of limping syndrome in young cats, there are numerous other potential causes of lameness, and if clinical signs are severe, or persist for longer than a few days, veterinary attention should always be sought.

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