Current Thoughts on FVRCP Vaccination
Michael R. Lappin, DVM, PhD, DACVIM
Fort Collins, CO, USA
It is always preferred to prevent rather than treat infections and prevention is best achieved by avoiding exposure to the infectious agent. Vaccines are available for some infectious agents and can prevent infection or lessen clinical illness when infection occurs. Feline herpesvirus 1 (FHV-1), calicivirus (FCV), and panleukopenia (FPV) are common feline viral agents. Each of these organisms can result in life-threatening disease in kittens and significant morbidity in adult cats. Several FVRCP vaccines are available and are commonly used in small animal practice. The vaccines are modified live for parenteral administration, modified live for topical administration, or killed and adjuvanted for parenteral administration. The American Association of Feline Practitioners1,2 and the Council on Biological and Therapeutic Agents3 have published information concerning cat vaccination guidelines in the last several years. The American Association of Feline Practitioners guidelines are endorsed by the American Animal Hospital Association and the American College of Veterinary Internal Medicine. It is recommended by most authors that all healthy kittens and adult cats without a known vaccination history should be routinely administered FVRCP vaccines. In kittens > 6 weeks of age, an FVRCP vaccine should be administered every 3 to 4 weeks until 12 weeks of age. In kittens > 12 weeks of age, an FVRCP vaccine should be administered twice, 4 weeks apart. A booster should be should be administered one year later. For most available FVRCP vaccines, boosters no more frequently than 3 years are recommended.
EFFICACY OF FVRCP VACCINES
Use of FHV-1 and FCV vaccines lessen clinical signs of disease when vaccinated cats are exposed to virulent strains of virus. Panleukopenia vaccination leads to sterilizing immunity. Panleukopenia vaccination can also lead to protection against CPV-2.4 Serological and challenge studies suggest that FVRCP vaccines can induce immunity that lasts at least 3 years.5-8 However, there are strains of FCV in naturally infected cats that are genetically distinct from vaccine strains. These strains have been isolated from FVRCP vaccinated cats.9-11
Efficacy of intranasal FVRCP vaccines have been reported over the years in several studies.12-17 A new formulation of a modified live FVRCP for intranasal administration (Feline UltraNasalTM FVRCP Vaccine, Heska Corporation, Fort Collins, CO) has just received a license in the United States. We recently completed a study (Unpublished data, 2005) to determine whether intranasal administration of one dose of this vaccine to kittens two, four, and six days before virulent FHV-1 challenge would lessen clinical signs and FHV-1 shedding when compared to unvaccinated control kittens. Three groups of 10 unvaccinated kittens were administered one dose of the vaccine two, four, or six days before challenge, respectively and one group was maintained as unvaccinated controls. FHV-1 challenge was then induced following USDA protocols and the kittens were observed for clinical signs of disease for 14 days. Throat swabs were collected from the group of kittens vaccinated on day -6 and the group of kittens used as controls on days -6, -3, 0, 4, 6, 8, and 12. Swabs were placed in sterile saline, incubated for 2 hours at room temperature, and frozen at -70°C until transported on dry ice for assay. FHV-1 and feline GAPDH DNA were amplified from each sample by use of a previously described fluorgenic PCR. Results for the fluorgenic assay for FHV-1 DNA were compared to cell count derived from a standard curve for GAPDH/cell to ensure an adequate cell count was present on the swab for analysis. When vaccinated kitten results were compared to control kitten results, cats vaccinated 6 or 4 days prior to challenge had significantly lower clinical scores (P < 0.05) than control cats. FHV-1 shedding was lower in kittens vaccinated six days prior to challenge than in control cats on day 6 after challenge (P < 0.05). We concluded that administration of this vaccine within several days prior to exposure lessened clinical signs of disease and FHV-1 shedding compared to unvaccinated cats.
In a separate study (Unpublished data, 2005),we assessed lymphocyte blastogenesis (LBT) in response to FHV-1 antigens and the non-specific mitogen concanavalin A (Con A) in cats after vaccination with five different FVRCP vaccines. FHV-1 negative kittens (n = 50) were purchased and randomly divided into five groups of 10. On days 0, 28, and 56, each group of kittens was administered the FVRCP vaccine for IN administration or one of four FVRCP vaccines for SQ administration. Blood was collected into heparin on days 67, 81, and 180. Whole blood LBT assays were performed using either FHV-1 UV inactivated antigens (equivalent to 400, 40, or 4 TCID50 per well) or concanavalin A (5µg/ml, 10µg/ml, or 20µg/ml per well) to stimulate cell division. Responses (stimulation indices) to Con A and FHV-1 antigens were log transformed prior to statistical analysis to normalize the residuals. Geometric means by group were calculated and data were analyzed using a repeated measures experiment (the MIXED procedure in SAS, SAS Institute, Cary, NC, Version 9.1). The statistical model included vaccine group, time, and the interaction between time and group as fixed effects. If the time by group interaction was statistically significant (P < 0.05), within time group effects were evaluated. Where within group effects were significant, group means were compared using Fisher's least significant difference test (LSD) in a pair-wise fashion. Group mean stimulation indices for both FHV-1 antigen and Con A were > 1 for each cat group on all collection days. A group by time interaction was detected for both Con A and FHV-1 (P < 0.05). Within time group effects were detected at 10 and 12 (P < 0.05), but not 26 (P > 0.05), weeks for each of these responses. At 10 weeks, cats vaccinated with the FVRCP-IN vaccine had significantly greater responses to Con A and FHV-1 as compared to cats vaccinated with each of the SC vaccines. At 12 weeks, cats vaccinated with the FVRCP-IN vaccine had significantly greater responses to both Con A and FHV-1 than cats in two of the four groups vaccinated with FVRCP vaccines SQ. These results suggest that cats administered the FVRCP-IN vaccine have greater or comparable cell mediated immune responses to FHV-1 antigens and Con A as cats administered FVRCP vaccines SQ for the first several months after vaccination. Challenge studies will be needed to further characterize how these findings relate to vaccine-induced FHV-1 immunity.
SAFETY OF FVRCP VACCINES
While very safe, modified live FVRCP vaccines have been associated with a number of clinical abnormalities including fever, infection of the fetus, induction of a chronic carrier state, polyarthritis, and upper respiratory tract disease.18-21 Parenteral administration of FVRCP vaccines occasionally leads to vaccination site sarcomas.22
We recently reported recombinant antigens of feline herpesvirus 1, calicivirus, and panleukopenia virus for use in serological assays.5 In the same work, we showed that serology could be used to accurately determine need for FVRCP vaccination in cats if validated assays are utilized. While titrating the recombinant antigen based ELISAs by comparing to ELISAs performed using whole viruses, we discovered that vaccinated cats make antibodies against a commonly used cell culture line. The Crandall-Reese feline kidney (CRFK) cell line has been used to propagate feline viruses for years. While isolated from a kidney, the cell line has characteristics of a fibroblast. During virus purification for vaccine production (FVRCP) or immunoassay development, it is impossible to remove all CRFK proteins or other cell constituents. Thus, CRFK proteins contaminate the viral preparations and commercially available FVRCP vaccines grown on the cell line contain CRFK proteins. As a consequence, during the course of routine immunization, cats are exposed to CRFK proteins and may mount an immune response against those proteins. Since the CRFK cell line is derived from a feline cell line, administration of FVRCP vaccines induces antibodies that also bind to feline renal tissues. We have now performed several studies to assess the problem. In the first, recently completed study,23 our objectives were to determine whether cats inoculated with FVRCP vaccines grown on the CRFK cell line develop antibodies against CRFK lysates or renal cell lysates (FRC), whether cats hypersensitized with CRFK lysate develop antibodies against CRFK cell lysates or FRC lysates, and whether FVRCP vaccination or hypersensitization with CRFK cell lysates induces clinical pathological or histopathological abnormalities over a 56 week period. We assessed three FVRCP vaccines for SQ administration and one FVRCP vaccine for intranasal/intraocular administration. CBC, serum biochemical panel, urinalysis, microalbuminuria assay, and ELISAs to detect antibodies against CRFK lysate or FRC lysate were performed on samples collected at intervals during the study. Renal biopsies were assessed for abnormalities independently by two pathologists. None of the cats was positive for antibodies against CRFK lysate or FRC lysate prior to inoculation. All six cats administered CRFK lysate alone were positive in the CRFK ELISA on multiple sample dates in the CRFK ELISA. Neither of the cats receiving intranasal/intraocular vaccination achieved the positive cutoff value in the CRFK ELISA. Five of the six cats administered a parenteral vaccine were positive in the CRFK ELISA at least once during the study. All six cats administered CRFK lysate were positive on multiple sample dates in the FRC ELISA. All six cats administered a parenteral vaccine were positive on multiple sample dates in the FRC ELISA. Neither of the cats administered the intranasal/intraocular vaccine were positive in the FRC ELISA. Significant CBC, serum biochemical, urinalysis, microalbuminuria, or histopathologic abnormalities were not detected during the study. We concluded that parenteral administration of vaccines grown on the CRFK cell line and SQ inoculation of CRFK lysate alone induced CRFK antibodies and FRC antibodies in most cats in this study. However, the clinical pathological and histopathological results suggest that even hypersensitization with CRFK proteins was not associated with detectable renal dysfunction, renal inflammatory disease, or glomerular disease in the 56-week time period studied.
In the original study, only small numbers of cats were assessed per group. Thus, a followup study was performed with 5 groups of cats (1 intranasal vaccine and 4 parenteral vaccines).24 In this study, we showed that parenteral administration of FVRCP vaccines induces a statistically greater magnitude of antibody response to CRFK proteins than intranasal administration of a FVRCP vaccine. We are in the process of determining the immunodominant CRFK antigens recognized by feline antibodies.25 To further assess for disease associations with administration of CRFK containing FVRCP vaccines, we are currently performing the following studies: 1. Determination of the source and distribution of CRFK proteins in feline tissues; 2. Determination of the CRFK protein concentrations in FVRCP vaccines available in the United States; and 3. Correlation of CRFK antibodies with presence of azotemia, uveitis, pancreatitis, and other idiopathic inflammatory diseases in cats of the United States.
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Michael R. Lappin, DVM, PhD, DACVIM
Colorado State University
Ft. Collins, CO