Feline immunodeficiency virus (FIV) has been associated with the development of malignant lymphoma in some cats. Lymphomas and leukemias account for approximately 30% of all feline neoplasms. Although no clear genetic predisposition to lymphoma development in general has been identified in cats, with the possible exception of intestinal lymphoma in young Siamese cats in association with inflammatory bowel disease, an association with either feline leukemia virus (FeLV) or FIV infection has been repeatedly documented from all over the world. It has previous been reported that FIV-infected cats are approximately five times more likely to develop lymphoma or leukemia than non-infected cats.
Researchers from School of Veterinary Science, University of Queensland in Gatton, Australia and their USA collaborators retrospectively studied spontaneous lymphomas in 20 FIV-positive cats. In this pilot study, all 20 lymphomas were positive for scattered FIV antigen with at least one of several monoclonal antibodies specific for an array of FIV proteins. The researchers argue that this finding may not be incidental but a cause and effect relation may have occurred. Nevertheless, in general, although FIV-positive have an increased risk for lymphoma, the incidence of lymphoma is often low relative to the prevalence of positive retroviral status, thus they speculate at other cofactors (e.g., other latent viral infections) may be necessary for FIV-positive cats to develop lymphoma.
The researchers note that in both humans and macaques, gamma-herpesviruses have been implicated in the development of lymphomas in retrovirus-infected individuals. In addition, various gamma-herpesviruses in various species have previously been shown to lead to lymphoproliferative disorders and increase the risk for lymphoma development. Recently, three distinct species-specific gamma-herpesviruses have been identified in domestic cats, bobcats, and pumas. Subsequent studies demonstrated a likely worldwide distribution of domestic cat gamma-herpesvirus with prevalence of infection varying from around 5% up to 25-30% of cats in different geographical areas. As a note, feline rhinotracheitis virus (FHV-1) that commonly causes upper respiratory symptoms in cats (i.e., cat cold) is an alpha-herpesvirus, not a gamma-herpesvirus.
Although, the researchers failed to demonstrate co-infection with FIV and Felis catus specific gamma-herpesvirus in all but one sample in the pilot study described herein, they argue that spontaneous cases of feline lymphoma still lend themselves to a systematic, prospective study to establish or refute an association between these two viruses in lymphoma development in FIV-positive cats. [GO]