Diagnosis and Treatment of Feline Calicivirus

Emily Thornton

Diagnosis

Diagnosis of calicivirus by veterinarians is often based solely off clinical signs. Although certain clinical signs (i.e. severe oral ulceration) tend to suggest calicivirus more so than other diseases, it is important in some cases to obtain a definitive diagnosis. Cats that become infected with calicivirus tend to become chronic shedders of the virus (some may shed for weeks to months, others may be life-long shedders), so in cases where there is more than one cat present in a household or in cattery situations, a definitive diagnosis is desired to prevent rapid spread of disease. The clinical signs of FCV can often mimic clinical signs of other diseases such as Feline Herpes Virus, Chlamydophila infection, or Bordatella infection. On initial presentation, the cat may show mixed clinical signs as secondary bacterial infections are possible with FCV infection. A definitive diagnosis is preferred in areas where there may be increased exposure/spread, if there is no response to symptomatic treatment of FCV, or if the virulent strain of FCV is suspected.

A definitive FCV diagnosis may be done by a variety of mechanisms which include PCR, virus isolation, and serology, although serology is often not recommended for two reasons: There are an increased number of FCV strains that may cause a varying titer response, and FCV vaccines may confound antibody response. Although serology may not be effective in diagnosing most FCV cases, it may have some use in identifying virulent systemic FCV. Virus isolation is another option for diagnosing FCV. Samples should include oropharyngeal, nasal, and/or conjunctival swabs (more swabs for better diagnosis). Virus isolation isn’t as sensitive in cats recovering from FCV infections, so a cat cannot be considered FCV-free from one negative sample taken over a week after the onset of clinical signs. Two or three negative samples on a weekly basis will confirm that the cat has stopped shedding the virus. Feline calicivirus may be diagnosed using PCR, but this may not be the best method of diagnosis due to the fact that FCV frequently mutates and develops new strains which may not all be detected by PCR methods. Something that should be taken into consideration with PCR detection of FCV is that there is an increased risk of false positives if there is contamination of the sample.

A new method to diagnose FCV is currently being researched to increase the sensitivity of PCR. There has been recent development of a nested PCR (nPCR) method which aims to isolate a primer sequence that is more conserved among the different strains of FCV. In a recent study, results have suggested increased sensitivity of nPCR tests compared to RT-PCR and virus isolation. The table below shows the results of the aforementioned study. There was approximately a 20% increase in diagnosis of FCV with nPCR compared to RT-PCR or virus isolation.

                     

Positive diagnostic results for FCV need to be considered in light of clinical signs and other possible infections (concurrent or otherwise). Cats that are FCV positive may be chronic shedders of the virus and may be showing clinical signs due to some other underlying disease which needs to be treated. Therefore, a FCV positive cat that does not respond to symptomatic treatment should be reevaluated.

Treatment

Unfortunately, FCV cannot be cured and treatment is only symptomatic. After a cat is infected, they tend to become chronic shedders, although it is possible for them to clear the virus completely. Severe oral ulcerations may cause the cat to become anorectic, and in those cases fluids and nutritional support are necessary. Often, affected animals need to be put on broad spectrum antibiotics to prevent secondary bacterial infections or treat concurrent infections. The virulent systemic form of FCV should be treated with more aggressive fluid and antibiotic therapy. These cats should also receive oral interferon alpha to boost the protective effects of natural immunity. There is some evidence suggesting that immunosuppressive doses of glucocorticoids may decrease mortality due to the virulent systemic strain, but more research needs to be done to confirm this. Confirmed FCV cases should be isolated to prevent further spread of disease, but strict isolation of virulent systemic cases is required due to the high mortality associated with the disease.

References: 

Hurley, Kate F., and Jane E. Sykes. "Update on Feline Calicivirus: New Trends." Veterinary Clinics of North America: Small Animal Practice 33.4 (2003): 759-72. SciVerse. ScienceDirect, July 2003. Web. 1 May 2013.

Marsillo, Fulvio, Barbara Di Martino, Nicola Dicaro, and Canio Buonavoglia. "A Novel Nested PCR for the Diagnosis of Calicivirus Infections in the Cat." Veterinary Microbiology 105.1 (2005): 1-7. SciVerse. ScienceDirect, 5 Jan. 2005. Web. 1 May 2013.