Applying a combination of semi-nested PCR and immunohistology (IHC), the presence of exogenous feline leukemia virus infection was studied in 302 necropsied cats with various disorders. 9% showed the classical outcome of persistent productive FeLV infection which was represented by FeLV antigen expression in different organs. 152 cats (50%) harboured exogenous FeLV-specific proviral sequences in the bone marrow but did not express viral antigen. These cats were considered as horizontally but non-productively infected.
Statistical evaluation showed a significant association of non-productive horizontal FeLV infection with a variety of parameters. Non-productively infected cats were statistically significantly older and more often originated from animal shelters than cats without exogenous FeLV infection. Furthermore, some pathological disorders like anemia, panleukopenia, and purulent inflammation showed significant association with non-productive FeLV infection. No significant association was found with lymphosarcoma, known for a long time to be induced by productive FeLV infection.