A comparison of haemagglutination, haemagglutination inhibition and PCR for the detection of psittacine beak and feather disease virus infection and a comparison of isolates obtained from Loriids

Psittacine beak and feather disease (PBFD) is recognized as a threat for endangered psittacine birds in Australia, New Zealand and South Africa. Several diagnostic methods for the detection of beak and feather disease virus (BFDV) infection have been developed but there are few studies comparing the relative merits or sensitivity and specificity of each diagnostic test. In this report, the results of PCR, haemagglutination (HA) and haemagglutination inhibition (HI) testing of diagnostic samples collected from 679 samples from a range of psittacine bird species suspected of being infected with BFDV are summarized and compared. There was a strong agreement (kappa = 0·757; P<0·0001) between PCR and HA testing of feather samples and PCR-negative birds were 12·7 times more likely to have HI antibody than PCR-positive birds. False-positive HA results with titres up to 1 : 320 were identified in six feather samples that were PCR negative; the haemagglutination detected in these samples was not inhibited by anti-BFDV antisera and was removed by filtration through a 0·22 μm filter. Similarly, one false-negative PCR result was detected in a feather sample that had a high HA titre (>1 : 40 960) and four false-positive PCR results were detected in a batch of four feather samples. Of 143 birds that were feather PCR positive, only two had detectable HI antibody, and these birds were also feather HA negative, suggesting that they were developing immunity to recent infection. All birds with HI antibody were negative on feather HA testing. The assays confirmed BFDV infection in two endangered swift parrots (Lathamus discolor) and phylogenetic analysis of the sequence data generated from ORF V1 of these isolates provide further evidence of BFDV genotypes clustering in parallel with the Loriidae, Cacatuidae and Psittacidae