Molecular Characterization of Hemorrhagic Enteritis Virus (HEV) Obtained from Clinical Samples in Western Canada 2017–2018

Hemorrhagic enteritis virus (HEV) is an immunosuppressive adenovirus that causes an acute clinical disease characterized by hemorrhagic gastroenteritis in 4-week-old turkeys and older. Recurrent incidence of secondary infections (e.g., systemic bacterial infections, cellulitis, and elevated mortality), may be associated with the presence of field-type HEV in Canadian turkey farms. We speculate that field-type HEV and vaccine/vaccine-like strains can be differentiated through analysis of the viral genomes, hexon genes, and the specific virulence factors (e.g., ORF1, E3, and fib knob domain). Nine out of sixteen spleens obtained from cases suspected of immunosuppression by HEV were analyzed. The limited data obtained showed that: (1) field-type HEV circulates in many non-vaccinated western Canadian flocks; (2) field-type HEV circulates in vaccinated flocks with increased recurrent bacterial infections; and (3) the existence of novel point mutations in hexon, ORF1, E3, and specially fib knob domains. This is the first publication showing the circulation of wild-type HEV in HEV-vaccinated flocks in Western Canada, and the usefulness of a novel procedure that allows whole genome sequencing of HEV directly from spleens, without passaging in cell culture or passaging in vivo. Further studies focusing more samples are required to confirm our observations and investigate possible vaccination failure.

Studies concerning the role of Hemorrhagic Enteritis Virus in the pathology of turkeys conducted in the Department of Poultry Diseases in Olsztyn over the last 30 years

In Poland, Hemorrhagic Enteritis Virus (HEV) was first isolated in 1987. Over nearly thirty years numerous studies concerning the pathology of HEV infection of turkeys were conducted at the Department of Poultry Diseases in Olsztyn. The results of these studies contributed to one postdoctoral dissertation, five doctoral dissertations and one master's thesis, as well as numerous publications and papers presented at national and international conferences. Over time, through the use of state of art laboratory techniques, such as flow cytometry and molecular biology, it has been demonstrated that Polish isolates of HEV are low pathogenic, but they possess strong immunosuppressive activity; moreover, these viruses occur very frequently in turkey flocks and are involved in pathological conditions of turkeys in our country. It has been further demonstrated that even the HEV isolates which are low pathogenic cause a subclinical course of the disease which impairs both humoral and cell mediated immune mechanisms, leading to exacerbation of ongoing disease processes and decreased vaccine induced immunity development, which consequently cause large economic losses in the turkey industry.