title: Comparison of serological assays for detecting antibodies in ducks exposed to H5 subtype avian influenza virus.
abstract: BACKGROUND
  Chicken red blood cells (RBCs) are commonly used in hemagglutination inhibition (HI) tests to measure hemagglutinating antibodies against influenza viruses. The use of horse RBCs in the HI test can reportedly increase its sensitivity when testing human sera for avian influenza antibodies. This study aims to compare the proportion of positives detected and the agreement between two HI tests using either chicken or horse red blood cells for antibody detection in sera of ducks experimentally infected or naturally exposed to Indonesian H5 subtype avian influenza virus. In addition, comparison with a virus neutralisation (VN) test was conducted with the experimental sera.
  
  
  RESULTS
  In the experimental study, the proportion of HI antibody-positive ducks increased slightly, from 0.57 when using chicken RBCs to 0.60 when using horse RBCs. The HI tests indicated almost perfect agreement (kappa = 0.86) when results were dichotomised (titre ≥ 4 log2), and substantial agreement (weighted kappa = 0.80) for log titres. Overall agreements between the two HI tests were greater than between either of the HI tests and the VN test. The use of horse RBCs also identified a higher proportion of antibody positives in field duck sera (0.08, compared to chicken RBCs 0.02), with also almost perfect agreements for dichotomized results (Prevalence and bias adjusted Kappa (PABAK) = 0.88) and for log titres (weighted PABAK = 0.93), respectively. Factors that might explain observed differences in the proportion of antibody-positive ducks and in the agreements between HI tests are discussed.
  
  
  CONCLUSIONS
  In conclusion, we identified a good agreement between HI tests. However, when horse RBCs were used, a higher proportion of sera was positive (titre ≥ 4 log2) than using chicken RBCs, especially during the early response against H5N1 virus. The HRBC-HI might be more responsive in identifying early H5N1 HPAI serological response and could be a recommended assay for avian influenza sero-surveillance in both wild and domestic birds.
authors: School of Veterinary Science, The University of Queensland, Gatton Campus, Gatton, QLD, Australia. j.henning@uq.edu.au
authors: Hendra
authors: H
authors: Wibawa
authors: Joerg
authors: J
authors: Henning
authors: Dessie Eri
authors: DE
authors: Waluyati
authors: Tri Bhakti
authors: TB
authors: Usman
authors: Sue
authors: S
authors: Lowther
authors: John
authors: J
authors: Bingham
authors: Akhmad
authors: A
authors: Junaidi
authors: Joanne
authors: J
authors: Meers
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D001315:Australia; D004372:Ducks; D004912:Erythrocytes / Q000737:chemistry / Q000276:immunology; D006385:Hemagglutination Inhibition Tests / Q000379:methods / Q000662:veterinary*; D007214:Indonesia; D053124:Influenza A Virus, H5N1 Subtype / Q000302:isolation & purification*; D005585:Influenza in Birds / Q000097:blood / Q000175:diagnosis / Q000821:virology*; D008137:Longitudinal Studies; D011201:Poultry Diseases / Q000097:blood / Q000175:diagnosis / Q000821:virology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D000914:Antibodies, Viral