Exposure of cats to low doses of FeLV: seroconversion as the sole parameter of infection

Abstract

In felids, Feline Leukemia Virus (FeLV) infection results in a variety of outcomes that range from abortive to progressive infection. Recently, a novel outcome was postulated for low FeLV infectious doses. Naïve cats exposed to faeces of persistently infected cats seroconverted, indicating infection, but remained negative for provirus and p27 antigen in blood. FeLV provirus was found in some tissues but not in the bone marrow, infection of which is usually considered a necessary stage for disease progression. To investigate the impact of low FeLV doses on young cats and to test our hypothesis that low dose exposure may lead to an unknown pathogenesis of infection without involvement of the bone marrow, 21 cats were infected oronasally with variable viral doses. Blood p27, proviral and viral loads were followed until week 20 post-infection. Tissue proviral loads were determined as well. The immune response was monitored by FeLV whole virus and p45 ELISA, FOCMA assay and Western blot. One cat showed regressive infection. In 7 cats, FOCMA assay positivity was the only sign of infection. Provirus was only found in some organs of the regressively infected cat. Here, we show that FeLV low dose exposure can result in seroconversion during a presumed abortive infection. Therefore, commonly used detection methods do not cover the whole spectrum of FeLV pathogenesis, leading to a possible underestimation of the effective occurrence of infection in the cat population