Determining the feline immunodeficiency virus (FIV) status of FIV-vaccinated cats using point-of-care antibody kits

Abstract

This study challenges the commonly held view that the feline immunodeficiency virus (FIV) infection status of FIV-vaccinated cats cannot be determined using point-of-care antibody test kits due to indistinguishable antibody production in FIV-vaccinated and naturally FIV-infected cats. The performance of three commercially available point-of-care antibody test kits was compared in a mixed population of FIV-vaccinated (n=119) and FIV-unvaccinated (n=239) cats in Australia. FIV infection status was assigned by considering the results of all antibody kits in concert with results from a commercially available PCR assay (FIV RealPCR™). Two lateral flow immunochromatography test kits (Witness FeLV/FIV; Anigen Rapid FIV/FeLV) had excellent overall sensitivity (100%; 100%) and specificity (98%; 100%) and could discern the true FIV infection status of cats, irrespective of FIV vaccination history. The lateral flow ELISA test kit (SNAP FIV/FeLV Combo) could not determine if antibodies detected were due to previous FIV vaccination, natural FIV infection, or both. The sensitivity and specificity of FIV RealPCR™ for detection of viral and proviral nucleic acid was 92% and 99%, respectively. These results will potentially change the way veterinary practitioners screen for FIV in jurisdictions where FIV vaccination is practiced, especially in shelter scenarios where the feasibility of mass screening is impacted by the cost of testing.

WSAVA Guidelines for the vaccination of dogs and cats

“…The VGG is aware that in some parts of the world, there remains a significant prevalence of FIV seropositivity and/or infection (Bennett et al 1989, Hosie et al 1989, Friend et al 1990, Glennon et al 1991, Bandecchi et al 1992, Hitt et al 1992, Ueland and Lutz 1992, Jones et al 1995, Hofmann-Lehmann et al 1996, Yilmaz et al 2000, Lee et al 2002, Muirden 2002, Norris et al 2007, Gleich et al 2009, Ravi et al 2010, Bande et al 2012, Chang Fung Martel et al 2013, Rypula et al 2014 [EB1]. There are now discriminatory serological tests (Kusuhara et al 2007, Levy et al 2008, Westman et al 2015 and more robust polymerase chain reaction (PCR) testing for the diagnosis of FIV infection (Arjona et al 2007, Wang et al 2010, Morton et al 2012 [EB1]. In many countries, it is most unlikely that cat owners will be persuaded to keep their cats indoors, away from the major risk of FIV transmission (bites by infected cats).…”

Diagnosing feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infection: an update for clinicians

“…SNAP Combo™ sold in Europe contains a third capture antigen (gp40) and we erroneously reported the Anigen Rapid™ test kit as detecting antibodies to p24 & gp40 following misinformation given by the manufacturer. 11 Our findings have since been reproduced overseas 29 and contributed to the upgrading of the FIV vaccine classification from 'not recommended' to 'non-core' in the most recent WSAVA Vaccination Guidelines (2015). Most importantly, SNAP Combo™ could not differentiate FIV-vaccinated and FIVinfected cats and had a low overall specificity, whereas Witness™, Anigen Rapid™ and FIV RealPCR™ could differentiate in most cases.…”

“…Based on the results from our first study, in which 109/119 recruited cats had received at least three annual FIV vaccinations, 11 we believe the transient false-positive antibody test results encountered in some cats with Witness™ and Anigen Rapid™ following a primary course of FIV vaccination do not occur following annual booster FIV vaccination and thus represent only a fraction of the lifetime of a FIV-vaccinated cat. However, more research is required to confirm this observation.…”

“…11 Our group conducted the first field study into the performance of Fel-O-Vax FIV® anywhere in the world by recruiting 301 client-owned Australian cats (89 FIV-vaccinated cases and 212 FIV-unvaccinated controls) and determining FIV infection status using the same diagnostic algorithm we used previously. This information is useful because it enables clinicians to quickly and easily identify FIV vaccine 'breakthroughs' prior to annual FIV vaccine administration and we know from our work that the FIV vaccine is not 100% effective in the field.…”

ELISA r-p24: optimization and validation of an enzyme immunoassay for the diagnosis of Feline Immunodeficiency Virus infections

“…The SNAP  Combo and SNAP  Combo Plus performances are 94% sensitivity and 100% specificity, and 100% sensitivity and 100% specificity, respectively. SNAP  Combo is available in Australia, New Zealand and North America, whilst SNAP  Combo Plus is available only in Europe (Westman et al, 2015). The Witness  FeLV/FIV (AGEN Biomedical Limited, Brisbane, Australia) detects antibodies against the GP40 protein whilst Antigen Rapid FIV/FeLV (Bionote, Korea) detects antibodies against GP40 and p24 proteins.…”