Ability to detect antibodies to beak and feather disease virus in blood on filter paper decreases with duration of storage

<jats:sec> <jats:title>Background</jats:title> <jats:p>Beak and feather disease virus (BFDV) is a circovirus that infects captive and wild psittacine birds, and is of conservation concern. The haemagglutination inhibition (HI) assay is used to determine antibody titres against BFDV, and the use of dried blood spots (DBS) on filter paper stored at room temperature has been suggested to be an equally valid technique to the use of frozen serum. However, research on other pathogens has found variable results when investigating the longevity of antibodies stored on DBS at room temperature. Consequently, we aimed to test the temporal stability of antibodies to BFDV in DBS samples stored long-term at room temperature. A further goal was to add to the current knowledge of antibody response to naturally acquired BFDV infection in crimson rosellas (<jats:italic>Platycercus elegans</jats:italic>).</jats:p> </jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Blood was collected from wild <jats:italic>P. elegans</jats:italic> in Victoria, Australia, that had been live-trapped (<jats:italic>n</jats:italic> = 9) or necropsied (<jats:italic>n</jats:italic> = 11). BFDV virus load data were obtained from blood stored in ethanol by real-time quantitative PCR (qPCR); antibody titres were obtained by HI assay from either DBS or serum samples, which had been collected concurrently. All HI assays were performed commercially by the Veterinary Diagnostic Laboratory (VDL) in Charles Sturt University, Australia, who were blind to BFDV blood status.</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>HI titres from DBS stored at room temperature declined significantly over time (~80 weeks). By contrast, frozen serum samples assayed after 80 weeks in storage all had high HI titres, only varying up to one dilution step from the initial HI titres obtained from DBS at 3–6 weeks after sampling. Weak HI titres from DBS samples all came back negative when the test was