The complexity of the interpretation of ELISA and RT-PCR results in the diagnosis of a reticuloendotheliosis virus infection: an extended case study

Reticuloendotheliosis virus (REV) is a species of the genus <i>Gammaretrovirus</i> that can cause neoplasia, immunosuppression, and runting-stunting syndrome. To show the clinical relevance of REV is complicated, and requires the demonstration of the virus, REV antibodies, the presence of typical gross and microscopic lesions, and the exclusion of other oncogenic agents in the case of the presence of tumours. Under field conditions, the first tests to be used might be a commercially available REV antibody ELISA or an RT-PCR to detect the REV genome. In this short paper, we present the experiences with two commercially available ELISAs and RT-PCR that we have gained from a REV outbreak on a large multi-age layer farm and many follow-up tests on samples from control farms with and without a known history of REV and fowlpox virus (FPV). In the field, some of the FPV field strains contain large inserts of the REV genome that might interfere with REV testing. The results of the ELISAs on sera from REV- and FPV- unsuspected flocks suggested that the cut-offs of both ELISAs were somewhat low resulting in a lower specificity. However, cut-offs of 2000 and 3050 for the IDEXX and BioChek ELISAs, respectively, gave an agreement of 100%, suggesting that these cut-offs might be advisable to use. The use of the combination of RT-PCR for REV and PCR for FPV proved to be very useful in separating REV infections from FPV infections. The results of our extended field study can help to interpret REV testing results.