Quantification of Feline immunodeficiency virus (FIV_pco) in peripheral blood mononuclear cells, lymph nodes and plasma of naturally infected cougars

Infection of domestic cats with Feline immunodeficiency virus (FIV) results in a fatal immunodeficiency disease, similar to Human immunodeficiency virus 1 (HIV-1) in humans. Elevated plasma viral loads in domestic cats are correlated to decreased survival time and disease progression. However, FIV is also maintained as an apathogenic infection in other members of the family Felidae including cougars, Puma concolor (FIV_pco). It is not known whether the lack of disease in cougars is a result of diminished virus replication. A real-time PCR assay was developed to quantify both FIV_pco proviral and plasma viral loads in naturally infected cougars. Proviral loads quantified from peripheral blood mononuclear cells (PBMC) ranged from 2.90 × 10¹ to 6.72 × 10⁴ copies per 10⁶ cells. Plasma viral loads ranged from 2.30 × 10³ to 2.81 × 10⁶ RNA copies ml^-1. These data indicate that FIV_pco viral loads are comparable to viral loads observed in endemic and epidemic lentivirus infections. Thus, the lack of disease in cougars is not due to low levels of virus replication. Moreover, significant differences observed among cougar PBMC proviral loads correlated to viral lineage and cougar age (P=0.014), which suggests that separate life strategies exist within FIV_pco lineages. This is the first study to demonstrate that an interaction of lentivirus lineage and host age significantly effect proviral loads.