Vaccination and Control of Feline Calicivirus

Erin Mathews

Vaccination 

There are three types of vaccines available against feline calicivirus. These include modified-live and killed parenteral vaccines and a modified-live intra-nasal vaccine. It is often included in a combination vaccine with feline herpes and panleukopenia viruses. Unlike most modified-live vaccines, the calicivirus vaccine must be boostered to confer maximum protection. Therefore, there may not be much benefit of the modified-live vaccine over a killed vaccine. The intra-nasal vaccine has a shorter onset of immunity than injectable vaccines. Vaccination for calicivirus produces a “non-sterile” immunity, meaning that it does not eliminate infection or development of a carrier state, but lessens the severity of clinical signs in infected cats and decreases shedding of the virus. There are numerous field strains of calicivirus, though the vaccine likely provides cross protection among strains.

Vaccine protocol for the average cat begins at around 9 weeks of age. The vaccine should be boostered twice, 3-4 weeks apart. The kitten should be at least 15 weeks old at the time of the last booster, since maternal antibodies may interfere with development of an appropriate immune response prior to this age. Adult cats should be vaccinated 1 year after their initial series and every 3 years thereafter.

For cats in high risk environments or during outbreaks, the vaccine can be administered as early as 2-4 weeks of age and boostered at 2 week intervals. Intra-nasal vaccines may be advantageous in these situations, since they may offer some protection within 72 hours of administration. It is important to note that intra-nasal vaccines may induce sneezing, which may be confused with active infection. For adult cats, vaccination prior to the 3 year recommendation may be beneficial if they are to be boarded at a kennel or exposed to new cats (such as foster kittens).

There is now a two strain vaccine available that incorporates a strain known to cause virulent-systemic disease. A study has proven its effectiveness when cats were challenged with the same strain they were vaccinated with. However, most strains that have been isolated from infected cats have arisen from new mutations and are not serologically cross reactive. The two strain vaccine does seem to provide better cross protection for traditional calicivirus infections.

Control

Feline calicivirus is non-enveloped, and therefore resistant to many common disinfectants. 5% bleach at a dilution of 1:32 has proven to be effective and should be used routinely to clean surfaces and instruments that come into contact with cats, especially those showing clinical signs. Other acceptable cleaners include potassium peroxymonosulfate (Trifectant) and chlorine dioxide. Without disinfection, the virus can survive for 28 days at room temperature.

An attempt should be made to minimize factors that predispose cats to infection with calicivirus. Among these are concurrent disease, poor nutrition, parasitism, stress, over crowding, and poor ventilation.

Suspected cases should be kept in strict isolation. Calicivirus can be transmitted on fomites, so these cats should be handled by a limited number of staff members. Gowns, gloves, and shoe covers should be utilized.

Outbreaks of virulent-systemic calicivirus pose an extreme challenge to shelters. All exposed cats must be considered at risk of transmitting the disease. There is no defined quarantine period, because the duration of viral shedding and for how long the virus maintains the mutation causing increased virulence is unknown. It is suggested that up to 3 months may be necessary. This period can be shortened by using viral culture and PCR to determine when quarantined cats are no longer shedding the virus. Due to intermittent shedding, 3 oropharyngeal swabs at 1 week intervals are required. This is not always the most effective allocation of a shelter's resources and many shelters may opt to euthanize these cats.

Often suspected cases of virulent-systemic calicivirus turn out to be an unrelated primary disease (such as panleukopenia) that is confounded by co-infection with traditional FCV. It is possible these diseases will be more amenable to treatment. Before extreme measures are enacted, care should be taken to rule out this scenario. The likelihood that virulent-systemic calicivirus is involved increases when otherwise healthy adult cats or well-vaccinated cats are affected.

References:

American Association of Feline Practitioners: Feline Vaccination Advisory Panel Report. Dec 29, 2006.

Huang C, Hess J, Gill M, Hustead D. “A dual-strain feline calicivirus vaccine stimulates broader cross-neutralization antibodies than a single-strain vaccine and lessens clinical signs in vaccinated cats when challenged with a homologous feline calicivirus strain associated with virulent systemic disease.” J Feline Med Surg. 2010 Feb;12(2):129-37

Rothrock, Kari. VIN Associate Database: Feline Calicivirus. Last updated on 5/25/2012.

UC Davis Koret Shelter Medicine Program. http://sheltermedicine.com/node/38#vacs