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Effect of vaccination against feline immunodeficiency virus on results of serologic testing in cats

Julie K. Levy DVM, PhD, DACVIM1, P. Cynda Crawford DVM, PhD2, and Margaret R. Slater DVM, PhD3
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  • 1 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.
  • | 2 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.
  • | 3 Department of Veterinary Anatomy and Public Health, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4458.

Abstract

Objective—To determine the effect of vaccination against FIV on results of serologic assays for FIV infection.

Design—Prospective clinical trial.

Animals—26 specific-pathogen-free cats, 102 laboratory- reared cats (42 unvaccinated and uninfected, 41 vaccinated and uninfected, and 19 infected with FIV), and 22 client-owned cats infected with FIV.

Procedure—To determine the onset and duration of anti-FIV antibody production in cats following vaccination with a whole-virus vaccine, serum was obtained from the 26 specific-pathogen-free cats prior to vaccination and weekly for 10 weeks, then monthly for 52 weeks, after vaccination; serum was tested for anti-FIV antibodies with lateral flow and microwell plate ELISAs. To determine the diagnostic performance of serologic assays for FIV infection, plasma from uninfected, unvaccinated cats; uninfected, vaccinated cats; and FIV-infected cats was tested for FIV antibodies with the 2 ELISAs, a western blot assay, and an immunofluorescence antibody assay and for FIV antigen with an ELISA.

Results—Anti-FIV antibodies were detected in all 26 vaccinated cats 1 year after vaccination. Sensitivity of the antibody assays for FIV infection was high (98% to 100%). Specificity was high in unvaccinated cats (90% to 100%) but poor in vaccinated cats (0% to 54%). None of the vaccinated or infected cats had detectable FIV antigen in plasma.

Conclusions and Clinical Relevance—Results suggest that vaccination against FIV causes false-positive results for at least 1 year with currently available serologic assays for FIV infection. Negative FIV antibody assay results are highly reliable for detection of uninfected cats, but positive results should be interpreted with caution. (J Am Vet Med Assoc 2004;225:1558–1561)

Abstract

Objective—To determine the effect of vaccination against FIV on results of serologic assays for FIV infection.

Design—Prospective clinical trial.

Animals—26 specific-pathogen-free cats, 102 laboratory- reared cats (42 unvaccinated and uninfected, 41 vaccinated and uninfected, and 19 infected with FIV), and 22 client-owned cats infected with FIV.

Procedure—To determine the onset and duration of anti-FIV antibody production in cats following vaccination with a whole-virus vaccine, serum was obtained from the 26 specific-pathogen-free cats prior to vaccination and weekly for 10 weeks, then monthly for 52 weeks, after vaccination; serum was tested for anti-FIV antibodies with lateral flow and microwell plate ELISAs. To determine the diagnostic performance of serologic assays for FIV infection, plasma from uninfected, unvaccinated cats; uninfected, vaccinated cats; and FIV-infected cats was tested for FIV antibodies with the 2 ELISAs, a western blot assay, and an immunofluorescence antibody assay and for FIV antigen with an ELISA.

Results—Anti-FIV antibodies were detected in all 26 vaccinated cats 1 year after vaccination. Sensitivity of the antibody assays for FIV infection was high (98% to 100%). Specificity was high in unvaccinated cats (90% to 100%) but poor in vaccinated cats (0% to 54%). None of the vaccinated or infected cats had detectable FIV antigen in plasma.

Conclusions and Clinical Relevance—Results suggest that vaccination against FIV causes false-positive results for at least 1 year with currently available serologic assays for FIV infection. Negative FIV antibody assay results are highly reliable for detection of uninfected cats, but positive results should be interpreted with caution. (J Am Vet Med Assoc 2004;225:1558–1561)