Circulation and molecular characterization of hemorrhagic enteritis virus (HEV) in commercial turkey and meat chicken flocks in Australia

Authors: GERBER, PRISCILLA - University Of New England; Spatz, Stephen; ALFIREVICH, SHERIDAN - Baiada Poultry; WALKDEN-BROWN, STEPHEN - University Of New England

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2021
Publication Date: 1/10/2022
Citation: Gerber, P.F., Spatz, S.J., Alfirevich, S., Walkden-Brown, S.W. 2022. Circulation and molecular characterization of hemorrhagic enteritis virus (HEV) in commercial turkey and meat chicken flocks in Australia. Avian Diseases. 66(1):53-59. https://doi.org/10.1637/21-00095.
DOI: https://doi.org/10.1637/21-00095

Interpretive Summary: Turkey adenovirus 3, also known as turkey hemorrhagic enteritis virus (HEV), causes a variety of clinical conditions in poultry, namely hemorrhagic enteritis (HE) in turkeys, marble spleen disease in pheasants, and splenomegaly in chickens. Infection with HEV was found to be ubiquitous in Australian poultry based on the high proportion of turkey spleen samples positive for HEV DNA and sera positive against HEV antibodies. Based on serological results, HEV infection appears widespread in chickens, but is less likely to be causing problems in that species. These results indicate a substantial circulation of HEV field strains in commercial flocks as vaccines against HEV are not used in the country. The Australian HEV sequences clustered together and separately from isolates originated from other countries, which is not surprising given the geographic distance between the sources. However, the number of point mutations leading to aa changes was significantly higher than previously reported indicating a more distant ancestry. Comparison of whole HEV genome sequence of Australian, Israeli and North American strains revealed mutations in gene coding regions that were conserved in all Australian strains. The mutations in the Australian HEV strains occurred throughout the genome, including polymorphisms shared with virulent strains in genes associated with virulence such as the ORF1 and fiber and polymorphism in genes encoding for proteins considered highly stable such as hexon and penton.

Technical Abstract: Currently, there is no available vaccine against hemorrhagic enteritis virus (HEV) in Australia. Although it is assumed that subclinical HEV infections occur and may be associated with an increase in colibacillosis in Australian commercial turkey flocks, the prevalence of infection with this virus in the country is largely unknown. The aims of this study were to determine the extent of HEV infection in commercial flocks in Australia and to investigate the diversity of Australian HEV strains. Serum and spleen samples were collected from breeder and grower turkeys and serum was collected from breeder and grower chickens by the two major poultry integrator companies in Australia. Of the turkey samples, 727/849 (86%) sera were positive for anti-HEV antibodies by ELISA. HEV DNA was detected in 215/278 (77%) spleen samples positive by PCR. Of the meat chicken sera, 115/144 (80%) samples were seropositive. Sequencing the whole genome of three HEV field isolates showed that the Australian strains are highly similar and cluster separately from strains from other geographic regions although several point mutations were shared with HEV strains considered to be virulent. In conclusion, HEV infection is ubiquitous in Australian commercial poultry flocks. The impact of the many genomic point mutations detected in Australian HEV strains on virus pathogenicity is unclear.