Epidemiology and diagnosis of feline retroviruses (FIV and FeLV) in Australia and a trial of FIV vaccine effectiveness in the field.

Abstract

Feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) remain important infections of domestic cats in Australia and overseas. This thesis begins by providing up-to-date Australian prevalence data in three cohorts of cats, comprising approximately 4,300 cats. Interestingly, the prevalence of both retroviral infections is higher in Perth, Western Australia compared to the rest of the country (Chapter 2). The diagnosis of FIV infection in FIV-vaccinated cats using fast, readily accessible, cheap point-of-care antibody kits, previously thought impossible, is reported in Chapter 3, which includes also the results of FIV testing using PCR methodology. This finding will expedite the diagnosis of FIV by veterinarians in most clinical scenarios encountered in the field, and has already contributed to changed recommendations concerning the use of the FIV vaccine (WSAVA Vaccination Guidelines, changed from ‘Not Recommended’ in 2010 to ‘Non-Core’ in 2015). Using the same cohort of cats and same antibody test kits, it was discovered that FIV infection can also be reliably diagnosed in FIV-vaccinated and FIV-unvaccinated cats using saliva by two of the kits tested (Chapter 4). The duration of antibody response in FIV-vaccinated cats using four commercially available FIV antibody test kits and a prospective study of client-owned kittens and cats, and the effect on point-of-care testing for FIV infection, is reported in Chapter 5. The first ever study into the effectiveness of the only currently commercially available FIV vaccine in the field is reported in Chapter 6. The effectiveness (protective rate) of the vaccine was determined to be 56%, and five confirmed vaccine ‘breakthroughs’ are discussed, these being the first vaccine breakthroughs observed in the field. This finding has stimulated renewed discussion about the effectiveness of the FIV vaccine (e.g. meeting of Key Opinion Leaders organised by Boehringer Ingelheim, The Shangri-La Hotel, Sydney, 24th June, 2016) and will likely lead to further studies in other countries using similar methodology. Diagnosis of FeLV infection was investigated using both blood and saliva as diagnostic specimens with the same three commercially available kits tested in Chapters 3 and 4 (kits were FIV/FeLV combination kits) and also an in-house real-time PCR assay, with one kit found to produce substantially more false-positive results using blood than the other two kits (Chapter 7). The combined outcomes of Chapters 3, 4 and 7 will provide guidance for Australian veterinarians on the most accurate FIV/FeLV test kits to use in practice, as well as introduce the concept to shelters and rescue organisations who currently routinely screen for FIV/FeLV that testing using saliva is a viable and less stressful alternative to testing using blood. Finally, an in-depth study of possible outcomes following FeLV exposure for the client-owned cats recruited for Chapter 6 and two cohorts of group-housed cats sampled from two different rescue facilities experiencing recent FeLV outbreaks is reported, leading to recommendations regarding FeLV testing and vaccination (Chapter 8).