Haemorrhagic enteritis of turkeys – current knowledge

Abstract

Haemorrhagic enteritis virus (HEV), an adenovirus associated with acute haemorrhagic gastro-intestinal disease of 6-11-week old turkeys predominantly hampers both humoral and cellular immunity. Affected birds are more prone to secondary complications (e.g. colibacillosis and clostridiosis) and failure to mount an effective vaccine-induced immune response. HEV belongs to the new genus Siadenovirus. Feco-oral transmission is the main route of entry of the virus and it mainly colonizes bursa, intestine and spleen. Both naturally occurring virulent and avirulent strains of HEVs are serologically indistinguishable. Recent findings revealed that ORF1, E3 and fib genes are the key factors affecting virulence. The adoption of suitable diagnostic tools, proper vaccination and biosecurity measures have restrained the occurrence of disease epidemics. For diagnostic purposes, the best source of HEV is either intestinal contents or samples from spleen. For rapid detection highly sensitive and specific tests such as quantitative real-time PCR based on Taq man probe has been designed. Avirulent strains of HEV or MSDV can be effectively used as live vaccines. Novel vaccines include recombinant hexon protein-based subunit vaccines or recombinant virus-vectored vaccines using fowl poxvirus (FPV) expressing the native hexon of HEV. Notably, subunit vaccines and recombinant virus vectored vaccines altogether offer high protection against challenge or field viruses. Herein, we converse a comprehensive analysis of the HEV genetics, disease pathobiology, advancements in diagnosis and vaccination along with appropriate prevention and control strategies.

Virus-induced immunosuppression in turkeys (<i>Meleagris gallopavo</i>): A review

“…Activation of macrophages leads to cytokines (IL-6, interferon type I and II, and TNF) production. Immunosuppressive is the consequence of the nitric acid production, stimulated by the interferon-II (IFN-II) (Dhama et al, 2017). Transient immunosuppression has been reported during clinical phase of the disease, with considerable depletion of IgM-bearing B cells (Rautenschlein et al, 2000b).…”

“…Moreover, depression in phytohemagglutinin (PHA) is also described in inoculated birds (Nagaraja et al, 1985). Secondary bacterial infections may extend the course of illness and increase mortality for an additional 2-4 weeks (Dhama et al, 2017). Increased predisposition to enteropathogenic Escherichia coli infection (Larsen et al, 1985;van den Hurk et al, 1994;Giovanardi et al, 2014) and clostridial dermatitis (Thachil and Nagaraja, 2013) has been well documented.…”

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

“…HEV is the etiological agent of hemorrhagic enteritis (HE), a disease characterized by immunosuppression in turkeys of >4-weeks of age. The disease has two presentations: (1) clinical disease consisting of depression, gastrointestinal hemorrhages, and transient immunosuppression followed by increased mortality (up to 80% for highly virulent strains due to blood loss and secondary infection with opportunists like Escherichia coli ) [ 6 , 7 , 8 ]; and (2) subclinical infection, consisting in immunosuppression and causing economical losses because of secondary bacterial infection, especially from Escherichia coli , and processing plant condemnations [ 7 , 9 , 10 ]. The immunosuppression caused by the subclinical infection increases the birds susceptibility to secondary bacterial infections which poses a problem for the judicious antibiotic use in farm animals, both being important problems for the turkey industry [ 11 ].…”

“…Despite this, some Canadian farmers do not regularly vaccinate their turkey flocks against HE due to the absence of clinical disease amidst seroconversion in the flocks, disregarding the potential immunosuppressive nature of these avirulent strains. Currently, HEV is immunosuppressive and responsible for morbidity and mortality [ 6 , 14 , 15 ].…”

Detection of novel adenovirus in sick pigeons

“…Birds are considered common hosts for AdVs, and this fact is mirrored by a large number of so-called fowl AdVs (FAdVs), described in chicken already several decades ago. Moreover, birds can be infected with genetically diverse adenoviruses of the family Adenoviridae [ 1 , 8 ], which are classified into three different genera, namely Atadenovirus (e.g., Duck atadenovirus A and Psittacine atadenovirus A) [ 16 , 19 ], Siadenovirus (e.g., Turkey siadenovirus A) [ 4 ], and Aviadenovirus , which includes twelve species, some of which are major bird adenoviruses ( https://talk.ictvonline.org/taxonomy/ ).…”