A survey of feline leukaemia virus antigenaemia among cats in eastern Austria: a retrospective analysis of serum samples routinely tested between 1996 and 2011

Firth, Clair L; Möstl, Karin

ELISAs are the most commonly used FeLV diagnostic tests in general practice, particularly since the introduction 25 For this purpose, PCR was used in the Department of Clinical Virology at the University of Veterinary Medicine in Vienna. However, it was not feasible to assign follow-up and confirmatory tests to individual cats in this retrospective analysis, so that the percentage of false-positive test results and transiently antigenaemic cats cannot be estimated here. Additionally, such tests may have been performed in other external diagnostic laboratories. For this reason, it was impossible to tell whether cats testing negative were regressively infected, as such animals do not have free antigen circulating in their blood stream but retain provirus in their bone marrow. 16 In order to estimate accurately the true prevalence of FeLV infection, random samples from the entire Austrian cat population and additional virus isolation or PCR would have been required, which were not available for this retrospective analysis of existing data. A Swiss study has reported that up to 10% of cats tested and found to be negative for FeLV antigen are provirus positive when analysed by PCR. 21 Similarly, the assessment of antigenaemic animals did not include the possibility of abortive infections, where the FeLV is eliminated by the cat's immune system prior to antigenaemia occurring. Demographic data sent with the sample were highly variable, with the year 2008 being particularly poor with respect to data quality of this kind. For this reason, analyses of the effect of age or sex on FeLV-positive results were less statistically powerful than the analysis of overall prevalence. It would also have been relevant to have analysed factors relating to the cats' household situations, such as whether the animal was clinically symptomatic, indoor dwelling, free roaming, vaccinated, and so on, as well as whether the animals were undergoing an initial FeLV test or were being retested. Unfortunately, given the retrospective nature of this study, such data were not available.