title: Serological investigation of highly pathogenic avian influenza H5N2 in ostriches (Struthio camelus).
abstract: An ostrich farm of 929 birds that tested polymerase chain reaction-positive for highly pathogenic avian influenza H5N2 in a single sample was designated for culling, despite no evidence of sero-conversion as assessed by haemagglutination inhibition (HI) tests. A month later and immediately prior to culling, all birds were bled and tested with an IDEXX avian influenza virus (AIV) nucleoprotein (NP)-specific enzyme-linked immunosorbent assay (ELISA) and a high sero-prevalence was detected. To address the question of whether the NP-specific antibodies detected indicated exposure to H5 or non-H5 subtypes (H6N2 and H1N2 strains were also circulating regionally at the time), we developed two H5-specific ELISAs, both based on a recombinant H5 HA1 antigen. The H5 indirect ELISA used a horseradish peroxidase ostrich IgY conjugate that we produced in chicken eggs. The single-chain variable fragment (scFv) competitive ELISA (H5 scFv cELISA) used a scFv derived from an H5-immune chicken scFv library. By comparing IDEXX AIV ELISA results with those of the two H5-specific ELISAs and HI tests, we determined that up to 89% of the flock had been exposed to H5N2 AIV. We also detected evidence of suspected vaccination, since 17% of sera contained antibodies against the H5 glycoprotein but not the NP protein. Comparative analytical sensitivity indicated that HI tests are likely to miss up to 35% of H5-positive samples, and thus we consider that H5/H7-specific ELISAs should replace HI tests for ostrich testing in future.
authors.affiliation: Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa. celia.abolnik@up.ac.za
authors.forename: Celia
authors.initials: C
authors.lastname: Abolnik
authors.forename: Jeanni
authors.initials: J
authors.lastname: Fehrsen
authors.forename: Adriaan
authors.initials: A
authors.lastname: Olivier
authors.forename: Wouter
authors.initials: W
authors.lastname: van Wyngaardt
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Fosgate
authors.forename: Charlotte
authors.initials: C
authors.lastname: Ellis
mesh_terms: D000818:Animals; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D006386:Hemagglutination Tests / Q000662:veterinary; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D053125:Influenza A Virus, H5N2 Subtype / Q000235:genetics*; D005585:Influenza in Birds / Q000453:epidemiology* / Q000821:virology*; D012680:Sensitivity and Specificity; D016036:Seroepidemiologic Studies; D013019:South Africa; D020310:Struthioniformes
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; C109963:hemagglutinin, avian influenza A virus