Serological investigation of highly pathogenic avian influenza H5N2 in ostriches (Struthio camelus)

Avian Pathol. 2013;42(3):206-14. doi: 10.1080/03079457.2013.779637. Epub 2013 Apr 22.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Enzyme-Linked Immunosorbent Assay / methods
  • Enzyme-Linked Immunosorbent Assay / veterinary*
  • Hemagglutination Tests / veterinary
  • Hemagglutinin Glycoproteins, Influenza Virus / genetics
  • Influenza A Virus, H5N2 Subtype / genetics*
  • Influenza in Birds / epidemiology*
  • Influenza in Birds / virology*
  • Sensitivity and Specificity
  • Seroepidemiologic Studies
  • South Africa
  • Struthioniformes*


  • Hemagglutinin Glycoproteins, Influenza Virus
  • hemagglutinin, avian influenza A virus