Recurrence of feline leukemia virus (FeLV) and development of fatal lymphoma in a cat with feline immunodeficiency (FIV) induced immune suppression

During a long-term study with the goal to determine the clinical outcome of late-stage FeLV and FIV infections, we observed in one of the ostensibly FeLV recovered cats that FeLV may reappear and lead to fatal disease many years after FeLV exposure. The cat had been infected with FIV, vaccinated against FeLV and challenged with the latter virus. Analysis of the sequence of the FeLV Envelope protein revealed the presence of three heavily mutated, full-length variants with 89 -91% amino acid identity to each other and 89-91% identity to the FeLV-A/Glasgow-1 challenge strain. So far, the biological significance of the presence of these evolved variants is not clear. Thus, it is the goal of the present study, to analyze the reappearance of FeLV and the occurrence of FeLV-related disease in this FIV-infected cat. The well-documented follow-up study should provide significant first insights into the biological relevance of FeLV provirus-positive, aviremic cats and deepen our understanding of the host-retrovirus interaction in general.