Testing kittens for FeLV and FIV (Proceedings) - Veterinary Healthcare
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Testing kittens for FeLV and FIV (Proceedings)


CVC IN KANSAS CITY PROCEEDINGS


Discordant test results occur when results of ELISA and IFA testing do not agree and may make it difficult to determine the true FeLV status of a cat. Most typically, this is an ELISA-positive and IFA-negative cat. Discordant results may be due to the stage of infection, the variability of host responses, or technical problems with testing. The status of the cat with discordant results may eventually become clear by repeating both tests in 60 days and yearly thereafter until the test results agree. Unfortunately, a significant number of these patients have persistently discordant test results and the cat's true status may not be known. Cats with discordant test results are best considered as potential sources of infection for other cats until their status is clarified.

PCR is offered by a number of commercial laboratories for the diagnosis of FeLV. PCR detects viral nucleic acid sequences (RNA or DNA) and can be performed on blood, bone marrow and tissues. PCR tests for FeLV are usually positive within one week of FeLV exposure. When performed by a well-equipped and well-trained laboratory, PCR can be the most sensitive test methodology for FeLV and could help resolve cases with discordant test results and detect regressive infections. Independent evaluation of commercial PCR testing for FeLV (or FIV) is not routinely performed nor are labs required to be licensed or regulated, so that veterinarians may not be able to ascertain the diagnostic efficacy of a test offered by a particular laboratory.

Recently, a real-time quantitative PCR assay was used to screen 597 Swiss cats for FeLV. Surprisingly, 10% of cats negative for FeLV p27 antigen by ELISA were positive by PCR (Hofmann-Lehmann, Huder et al. 2001). However, the proviral loads of these cats were 300-fold lower than for ELISA-positive cats. One possible explanation for the PCR-positive, ELISA-negative cat is that such cats are truly infected with FeLV but were able to overcome antigenemia (regressive infection). It is also possible that these cats were in the early stages of FeLV-infection and had not yet become ELISA-positive. Research such as this suggests it may be very difficult to determine the true status of cats that appear to be transiently infected and recovered.

References

Bienzle, D., F. Reggeti, et al. (2004). "The variability of serological and molecular diagnosis of feline immunodeficiency virus infection." Can Vet J 45(9): 753-7.

Crawford, P. C., M. R. Slater, et al. (2005). "Accuracy of polymerase chain reaction assays for diagnosis of feline immunodeficiency virus infection in cats." J Am Vet Med Assoc 226(9): 1503-7.

Goldkamp, C. E., J. K. Levy, et al. (2008). "Seroprevalences of feline leukemia virus and feline immunodeficiency virus in cats with abscesses or bite wounds and rate of veterinarian compliance with current guidelines for retrovirus testing." J Am Vet Med Assoc 232(8): 1152-8.

Hartmann, K., R.-M. Werner, et al. (2000). "Comparison of different practice tests for rapid diagnosis of feline immunodeficiency and feline leukemia virus infection (ESVIM abstract)." J Vet Intern Med 14(2): 232.

Hofmann-Lehmann, R., J. B. Huder, et al. (2001). "Feline leukaemia provirus load during the course of experimental infection and in naturally infected cats." J Gen Virol 82(Pt 7): 1589-96.

Levy, J., J. Richards, et al. (2001). "Feline retrovirus testing and management." Comp Contin Edu Pract Vet 23(7): 652-657.

Levy, J. K., P. C. Crawford, et al. (2008). "Differentiation of feline immunodeficiency virus vaccination, infection, or vaccination and infection in cats." J Vet Intern Med 22(2): 330-4.

Levy, J. K., P. C. Crawford, et al. (2004). "Effect of vaccination against feline immunodeficiency virus on results of serologic testing in cats." J Am Vet Med Assoc 225(10): 1558-61.

MacDonald, K., J. K. Levy, et al. (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 225(10): 1554-7.

Pepin, A. C., R. Tandon, et al. (2007). "Cellular segregation of feline leukemia provirus and viral RNA in leukocyte subsets of long-term experimentally infected cats." Virus Res 127(1): 9-16.


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