Relevance of the variability of the feline immunodeficiency virus in regard to pathogenicity and vaccination in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Manawatū, New Zealand

Cats infected with the feline immunodeficiency virus (FIV) show a range of clinical signs. Given the variability of the FIV genome, it is possible that there is variation in certain biological characteristics of FIV, such as pathogenicity. This may also be relevant to vaccination against FIV, as an effective vaccine would have to result in the generation of T cells that recognise a range of different variants in the field. The Fel-O-Vax® FIV vaccine has been available to veterinarians in New Zealand (NZ) for the past 12 years. Despite this, there is a paucity of studies investigating the cross-reactivity of the vaccine-induced immune response against different variants of FIV, and no studies investigating the efficacy of the vaccine in NZ. The overall aim of the research in this thesis was to determine the relevance of the variability of FIV, in regard to pathogenicity and vaccination in NZ. Firstly, 2 separate assays were designed to assess variation in the ability of different isolates of FIV to induce apoptosis or inhibit mitogen-induced proliferation in lymphoid cells in vitro. Results showed that variation in FIV-apoptosis did occur, supporting the argument that FIV variants may also differ in pathogenicity. Secondly, the cross-reactivity of the vaccine-induced immune response was assessed in vitro and in vivo, by measuring antigen-specific cellular activation and a delayed type hypersensitivity (DTH) response in vaccinated cats following inoculation with NZ field isolates of FIV. Results showed that the response was at least partially cross-reactive, however quantitative differences were detected in the response to each isolate of FIV tested. Finally, efficacy of the Fel-O-Vax® FIV vaccine under NZ conditions was investigated by comparing the prevalence of FIV in vaccinated and unvaccinated cats in the field. Results showed that there was no effect of vaccination on FIV prevalence, suggesting poor efficacy of the Fel-O-Vax® FIV vaccine in NZ. Results described in this thesis support the argument that there is variation among FIV in NZ, and that this may affect pathogenicity and vaccine efficacy in this country. The evidence presented did not support use of the Fel-O-Vax® FIV vaccine in NZ