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Compendium September 2009 (Vol 31, No 9)

Letters — AAFP Retrovirus Guidelines

    I read the recent Feline Focus article (June 2009) on FeLV/FIV testing and vaccination guidelines and wanted to make a brief comment about the FIV vaccine. As the article implies, vaccination with the FIV vaccine interferes with the ability to test cats for FIV infection because vaccinated cats will have positive FIV test results. Our clinic recently referred a cat to a university hospital for kidney transplant consultation. The cat was declined because it had received the FIV vaccine and therefore tested positive for FIV. Although the university knew we had vaccinated this cat, the pet was not a candidate for kidney transplantation because immunosuppressive drugs would be used to regulate organ rejection, and if the cat was truly infected, these drugs would cause a detrimental outcome. The university's rationale was that, at present, there is no reliable test to differentiate vaccinated from naturally infected cats. Therefore, another important, if uncommon, criterion that veterinarians need to assess before administering the FIV vaccine is whether their client would pursue kidney transplantation if their cat developed kidney disease in the future.

    Marguerite Hoey, DVM
    Kearny, New Jersey

    The Editor's Reply

    Thank you very much for sharing your experience. Most veterinarians would not readily think of this repercussion given that recommendations for renal transplantation are still relatively uncommon. However, it is a very real concern because of the inability to distinguish between antibodies induced by vaccination and those induced by infection.1 It is also theoretically possible for a cat to possess wild-type and vaccination antibodies from having been both infected and vaccinated because we do not conclusively know the full spectrum of serovar (serotype/strain/clade) protection afforded by the existing vaccine.

    Five subtypes, or clades, of FIV have been characterized and are classified by the letters A through E. Other subtypes may exist in nature. The most common FIV subtypes in North America are A, B, and C. The current FIV vaccine contains a mix of subtype A (Petaluma strain) and subtype D (Shizuoka strain) virus. The challenge virus used in the licensing study was a subtype A virus (strain not identified). Two subsequent studies evaluated protection against infection with two different subtype B strains. In one, 100% protection was noted2; in the other, less than 100% protection was achieved.3 Another study using a subtype A strain was not protective, and 100% of the cats, both control and vaccinated, became infected when challenged.4

    Many thanks for bringing this concern regarding vaccination and lack of suitability for a renal transplantation program to our attention.

    Margie Scherk, DVM, DABVP (Feline Medicine)
    Series Editor, Feline Focus

    Downloadable PDF

    1. Levy JK, Crawford PC, Slater MR. Effect of vaccination against feline immunodeficiency virus on results of serologic testing in cats. JAVMA 2004;225:1558-1561.

    2. Pu RY, Coleman J, Coisman J, et al. Dual-subtype FIV vaccine (Fel-O-Vax® FIV) protection against a heterologous subtype B FIV isolate. J Feline Med Surg 2005;7:65-70.

    3. Kusuhara H, Hohdatsu T, Okumura M, et al. Dual-subtype vaccine (Fel-O-Vax FIV) protects cats against contact challenge with heterologous subtype B FIV infected cats. Vet Microbiol 2005;108:155-165.

    4. Dunham SP, Bruce J, Mackay S, et al. Limited efficacy of an inactivated feline immunodeficiency virus vaccine. Vet Rec 2006;158:561-562.

    References »

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