Update on FeLV and FIV testing: it's a new world
UPDATE ON FELV & FIV TESTING: IT’S A NEW WORLD
Susan Little, DVM, DABVP (Feline)
Bytown Cat Hospital, Ottawa, Ontario, Canada
-United States (Burling et al, J Am Vet Med Assoc 2017):
West: FeLV 3.3%, FIV 3.9%
Midwest: FeLV 3.7%, FIV 3.3%
Northeast: FeLV 2.4%, FIV 3.3%
South: FeLV 3.1%, FIV 4.0%
-Canada (Little et al, Can Vet J, 2009)
FeLV range: 6.6% in Quebec & Nova Scotia, 2.6% in Ontario
FIV range: 7.1% in Quebec & Saskatchewan, 3.8% in Ontario
Transmission and risk factors for infection
-FeLV: transmitted primarily via saliva (grooming, bite wounds), queen to kittens
-FIV: transmitted primarily in saliva via bite wounds; queen to kittens is uncommon
-Oral disease: 1 in 5 cats with stomatitis is retrovirus-positive; almost 1 in 5 cats with bite wounds or abscesses are retrovirus-positive
-Retroviruses have little or no environmental persistence; readily inactivated by most disinfectants; not spread by indirect contact
-Testing and identification of infected cats is still the cornerstone of control
-Antibody: soluble; patient-side and multi-well; various target antigens
-Western blot: various target antigens
-Nucleic acid: PCR for proviral DNA, viral RNA; not suitable for screening; positive result with a validated test confirms infection, negative result cannot completely rule out infection.
-Patient-side test kits vary in ability to distinguish natural infection from vaccination
-Kittens: may acquire FIV antibodies in colostrum from a vaccinated or naturally infected queen; most kittens lose maternally-acquired antibodies by 12 weeks of age
-When a kitten tests FIV positive consider re-testing in 1 month or re-testing now with a validated PCR test
-When an adult cat tests FIV positive, consider re-testing with a different brand of patient-side test if the cat may have been FIV-vaccinated in the past or re-testing now with a validated PCR test
FeLV clinically relevant stages of infection
FeLV status may be fluid, not a static disease state in all cats
Abortive: virus is eliminated before proviral integration, infection is prevented
Regressive: cat is infected but infection is controlled by the cat’s immune system, unlikely to shed virus, low risk of FeLV-related disease unless infection is reactivated
Progressive: cat is infected, virus is shed in saliva, higher risk for FeLV-related disease
-Antigen: soluble, patient-side and multi-well (p27 antigen); cellular (IFA)
-Nucleic acid: PCR for proviral DNA, viral RNA
-FeLV vaccination does not interfere with testing; maternal immunity does not interfere with testing
-Understanding FeLV test results is evolving.
-Healthy cats negative on whole blood with a reliable test are likely to be negative unless last potential exposure was <30 days ago.
-Cats positive on patient-side tests can be re-tested with referral lab ELISA or PCR.
-It may not be possible to determine a cat’s infection status based on the results of any single test from a sample collected at a single point in time. Repeat testing over time may be required to determine if some cats have regressive vs progressive infection.
-FeLV infection can be spread via blood transfusion from cats that have regressive infections; care must be taken in testing potential blood donors.
Resources and reading
2013 AAFP Feline Vaccination Advisory Panel Report: Disease Information Fact Sheets
European Advisory Board on Cat Diseases Guidelines
Buch J, Beall M et al. Worldwide Clinic-Based Serologic Survey of FIV Antibody and FeLV Antigen in the Cat; ACVIM Forum 2017
Burling AN, Levy JK, Scott HM, Crandall MM, Tucker SJ, Wood EG, et al. Seroprevalences of feline leukemia virus and feline immunodeficiency virus infection in cats in the United States and Canada and risk factors for seropositivity. J Am Vet Med Assoc. 2017;251(2):187–94.
Kornya MR, Little SE, Scherk MA, et al. (2014). Association between oral health status and retrovirus test results in cats. J Am Vet Med Assoc, 245(8), 916–22.
Levy JK, et al. (2017). Performance of 4 Point-of-Care Screening Tests for Feline Leukemia Virus and Feline Immunodeficiency Virus. J Vet Intern Med, 31(2), 521–526.
Little, S., Sears, W., Lachtara, J., & Bienzle, D. (2009). Seroprevalence of feline leukemia virus and feline immunodeficiency virus infection among cats in Canada. Can Vet J, 50(6), 644–648.
Litster AL. (2014). Transmission of feline immunodeficiency virus (FIV) among cohabiting cats in two cat rescue shelters. Vet J, 201(2), 184–88.
MacDonald, K., Levy, J. K., Tucker, S. J., & Crawford, P. C. (2004). Effects of passive transfer of immunity on results of diagnostic tests for antibodies against feline immunodeficiency virus in kittens born to vaccinated queens. J Am Vet Med Assoc Vet Med Assoc, 225(10), 1554–1557.
Wardrop KJ, et al. (2016). Update on canine and feline blood donor screening for blood-borne pathogens. J Vet Intern Med, 30(1), 15–35.
Westman, M. E., Malik, R., Hall, E., Sheehy, P. A., & Norris, J. M. (2015). Determining the feline immunodeficiency virus (FIV) status of FIV-vaccinated cats using point-of-care antibody kits. Comp Immunol Microbiol Infect Dis 42, 43–52.