Objective: To determine the FIV status of Australian cats with lymphosarcoma and relate this to patient characteristics, tumour characteristics (tissue involvement, histological grade and immunophenotype), haematological and serum biochemical values and FeLV status of affected cats.
Design: Prospective study of 101 client-owned cats with naturally-occurring lymphosarcoma.
Procedure: Western blot analysis, ELISA and immunochromatography were used to detect FIV antibodies in serum from cats with lymphosarcoma.
Results: On the basis of Western blot analysis (which was considered the most accurate method for determining FIV status), 50/101 (50%) of cats with naturally-occurring lymphosarcoma were positive for FIV antibodies. Of these 50 cats, 35 had tumours of B-cell phenotype, 13 had T-cell tumours and 2 had tumours classified as non-B/non-T. Tumours from eight of these FIV-positive cats contained FeLV gene sequences, including a 9-month-old cat with FeLV antigenaemia. Compared with FlV-negative cats with lymphosarcoma, FIV-positive cats were more likely to be domestic crossbreds (P = 0.004), male (P = 0.048) and have atypical (especially nasal) forms of lymphosarcoma (P = 0.09). Only 39 of 107 (36%) blood or sera tested using ELISA were positive for FIV antibodies (including 5 false-positives).
Conclusions: The prevalence of FIV infection was considerably higher in our cohort of cats compared with series of lymphosarcoma cases from the Northern hemisphere. A positive FIV status was strongly associated with lymphosarcoma in Australian cats and it is possible that this infection may predispose to the development of lymphoid neoplasia. The presence of FIV infection would have been underestimated if commercial kits alone had been used for serology.