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 was also 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 discharges, 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, 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.