Hemorrhagic Enteritis Of Turkeys Research Articles

Turkey Hemorrhagic Enteritis (THE): A Short Overview.

Turkey Hemorrhagic Enteritis (THE) is an acute disease caused by a Siadenovirus that affects 4 week-aged and older turkeys, characterized by acute depression, bloody droppings, and a high mortality rate. The immunosuppressive attributes of THE can protract disease progression and create a predisposition in birds towards subsequent bacterial infectiodoralns involving Escherichia coli and Clostridium perfringens (necrotic enteritis). Turkey Hemorrhagic Enteritis Virus (THEV) predominantly affects turkeys and carries substantial economic implications for this industry. Macrophages and B lymphocytes are recognized as the predominant target cells for the virus, while the spleen is the principal site of viral replication. Infected cells have also been observed in various other tissues, including the intestines, bursa of Fabricius, cecal tonsils, thymus, liver, kidney, peripheral blood leukocytes, and lungs. The economic relevance of this disease is derived both from the high mortality rate, which can reach 60% depending on the virulence of the strain, and from subclinical disease responsible for poor performance in vaccinated animals. This review aims to provide a comprehensive overview of THE, spanning etiology, epidemiology clinical signs and gross lesions, prevention, and management.

Characterizing the splice map of Turkey Hemorrhagic Enteritis Virus

BackgroundHemorrhagic enteritis, caused by Turkey Hemorrhagic Enteritis Virus (THEV), is a disease affecting turkey poults characterized by immunosuppression and bloody diarrhea. An avirulent THEV strain that retains the immunosuppressive ability is used as a live vaccine. Characterizing the splice map of THEV is an essential step that would allow studies of individual genes mediating its immunosuppressive functions. We used RNA sequencing to characterize the splice map of THEV for the first time, providing key insights into the THEV gene expression and mRNA structures.MethodsAfter infecting a turkey B-cell line with the vaccine strain, samples in triplicates were collected at 4-, 12-, 24-, and 72-hours post-infection. Total RNA was extracted, and poly-A-tailed mRNA sequenced. Reads were mapped to the THEV genome after trimming and transcripts assembled with StringTie. We performed PCR of THEV cDNA, cloned the PCR products, and used Sanger sequencing to validate all identified splice junctions.ResultsResearchers previously annotated the THEV genome as encoding 23 open reading frames (ORFs). We identified 29 spliced transcripts from our RNA sequencing data, all containing novel exons although some exons matched some previously annotated ORFs. The three annotated splice junctions were also corroborated by our data. During validation we identified five additional unique transcripts, a subset of which were further validated by 3’ rapid amplification of cDNA ends (3’ RACE). Thus, we report that the genome of THEV contains 34 transcripts with the coding capacity for all annotated ORFs. However, we found six of the previously annotated ORFs to be truncated ORFs on the basis of the identification of an in-frame upstream start codon or the detection of additional coding exons. We also identified three of the annotated ORFs with longer or shorter isoforms, and seven novel unannotated ORFs that could potentially be translated; although it is beyond the scope of this manuscript to investigate whether they are translated.ConclusionsSimilar to human adenoviruses, all THEV transcripts are spliced and organized into five transcription units under the control of their cognate promoters. The genes are expressed under temporal regulation and THEV also produces multiple distinctly spliced transcripts that code for the same protein. Studies of the newly identified potential proteins should be urgently performed as these proteins may have roles in THEV-induced immunosuppression. Also, knowing the splicing of THEV genes should be invaluable to future research focusing on studying THEV genes, as this will allow accurate cloning of the mRNAs.

Avian adenovirus infections: diversity of pathogens, hazard to poultry industry and problems of immunoprophylaxis (review)

The data on diversity of adenovirus pathogens in nature and the role of the main representatives of the Adenoviridae family in poultry infectious pathology are presented. Special attention is paid to problematic issues of immunoprophylaxis due to lack of cross-immunity between different virus serotypes. There is no single and effective approach in the global strategy of immunoprophylaxis of avian adenoviruses, therefore, improving the means of avian adenovirus disease control is an urgent and important task. Avian adenovirus infections are represented by different nosological units: egg drop syndrome, hydropericardium syndrome, adenoviral gizzard erosion, marbled spleen disease of pheasants, hemorrhagic enteritis of turkeys, inclusion body hepatitis and many unclassified diseases. The paper provides data on the main nosological forms of adenovirus infections that pose a threat to cost-effective poultry farming, and highlights test results obtained by foreign authors on the effectiveness of some vaccines against adenovirus infection. Most vaccines have been developed to prevent avian hydropericardium syndrome, however, occurrence of many virus serotypes requires effective means of prevention and diagnosis in order to control other infections caused by adenoviruses. There is no registered vaccine against adenovirus infections that cause inclusion body hepatitis and adenoviral gizzard erosion. At the same time, inclusion body hepatitis alone accounts for 2.9% of all recorded avian infectious diseases. Vaccines registered in the Russian Federation are not enough to fully control these infections, and that requires a timely solution to the problem. The variety of avian adenoviruses determines the problems of their differential diagnosis and specific prevention.

An Explorative Study of the Causal Pathogenesis of Green Liver Discoloration in Organically Reared Female Bronze Turkeys (Meleagris gallopavo) Considering the Infectious Risk Factors

A recent study revealed that organically raised Bronze turkeys showed a high prevalence of green liver discoloration. This alteration is commonly associated with the Turkey Osteomyelitis Complex and potentially caused by opportunistic bacteria. Therefore, 360 organically fattened Bronze turkeys were examined post-mortem throughout two fattening trials with two examinations each to determine possible infectious risk factors and reduce disease prevalence. Clinical and pathoanatomical examinations were performed on every hen. Histopathological, bacteriological, parasitological, and virological examinations were performed on at least six hens without and, if applicable, six hens with green livers on each examination date. Overall, 9.0% of all hens had a green liver without a correlation with bacterial or parasitological findings but multiple health impairments. The discoloration correlated significantly with the detection of immunosuppressive turkey hemorrhagic enteritis virus at the early stage and macro- and histological joint/bone lesions at the late fattening stage, indicating the presence of two different predisposing pathogeneses. Flocks not being vaccinated against hemorrhagic enteritis but having a virus-positive sample showed the highest prevalence of green liver discoloration and developed worse in various parameters. In conclusion, an adequate vaccination schedule and the prevention of field infections may lead to a decreased risk of performance reduction and improved animal health.

Monitoring of a virulent turkey hemorrhagic enteritis virus on MDTCRP-19 cells by real time PCR

Monitoring of a virulent turkey hemorrhagic enteritis virus on MDTCRP-19 cells by real time PCR

Turkey Hemorrhagic Enteritis Virus Can Be Titrated but Not Propagated in Chicken Embryos.

This study aimed to investigate the feasibility of propagating and titrating hemorrhagic enteritis virus (HEV) in chicken embryos. A total of 308 embryonated eggs were used. At 10 days of embryonic age, eggs were inoculated via allantoic sac or chorioallantoic membrane routes with non-heat-treated (live) HEV or heat-treated (dead) HEV or served as negative controls. Allantoic fluid retrieved at 0, 1, 3, 5, and 7 days postinoculation (dpi) was tested for HEV by quantitative PCR. Inoculation with HEV did not cause visible growth impairment or lesions in the chicken embryos. Overall, there was no difference in postinoculation mortality rates among groups sham-inoculated (6/30, 20.0%) or inoculated with live (34/252, 13.4%) or dead (3/ 26, 6.9%) HEV (P = 0.58). The amount of HEV DNA detected in allantoic fluid at 7 dpi in eggs inoculated with live virus was similar to the inoculated dose, indicating that virus propagation in chicken embryos is not efficient. No HEV DNA was detected after 3 dpi in eggs inoculated with dead virus. Inoculation of chicken embryos combined with qualitative PCR can be used for titration of HEV virus stocks and presents a high correlation with in vivo titration using chickens (R2 0.98, P = 0.007). This method may be relevant in countries in which specific-pathogen-free turkeys are unavailable and in which the importation of RP19 cells, the only cell that supports effective propagation of HEV, is not permitted.

Propagation of an Avirulent Turkey Hemorrhagic Enteritis Virus Isolate in Chickens.

A series of studies were undertaken to optimize the propagation of hemorrhagic enteritis virus (HEV) in specific-pathogen-free (SPF) chickens. A total of 562 SPF chickens were orally inoculated with an Australian avirulent HEV isolate of turkey origin at 9, 14, 21, or 28 days of age with 5, 6, 7, or 8 log 10 genomic copies (GC), while 102 chickens served as uninfected controls. No clinical signs were observed in infected chickens. There was an inoculum-dose-dependent increase in the relative spleen and liver weight ( P < 0.01). Relative spleen weight 7 days post-HEV inoculation was up to 85% higher in chickens that were inoculated with 6 to 7 GC compared with controls, with no further increase at higher doses. Relative liver weight increased up to 14% in chickens inoculated with 6 GC, with no further increase. Birds inoculated with a 7 GC dose had a higher frequency of HEV DNA-positive birds (77% to 86%) than birds inoculated with lower doses (33% to 59%; P < 0.01). The most efficient dose for live passage propagation was 7 GC inoculated in 9-to-14-day-old birds, yielding an infection rate of 81%. Livers and spleens from infected birds at all doses were processed to produce a putative vaccine with a final GC recovery in the vaccine material of 8.6 GC/bird. In summary, HEV of turkey origin can be readily propagated in SPF chickens, and conditions to maximize viral retrieval were established.

Real-time PCR-based infectivity assay for the titration of turkey hemorrhagic enteritis virus, an adenovirus, in live vaccines

The current in vitro titration method for turkey hemorrhagic enteritis virus (THEV) is the end-point dilution assay (EPD) in suspension cell culture (CC). This assay is subjective and results in high variability among vaccine lots. In this study, a new in vitro infectivity method combining a SYBR Green I-based qPCR assay and CC was developed for titration of live hemorrhagic enteritis (HE) CC vaccines. The qPCR was used to determine the virus genome copy number (vGCN) of the internalized virus particles following inoculation of susceptible RP19 cells with 1 vaccine label dose. The measured vGCN represents the number of infectious viral particles (IVP) per 1 dose. This method was used to compare 9 vaccine lots from 3 companies in the United States. Significant lot-to-lot variations within the same company and among the various companies were found in genomic and qPCR-based infectious titer per label dose. A positive linear relationship was found between qPCR infectious titer and genomic titer. Further, considerable variations in CCID50 titers were found among tested vaccine lots, indicating the high variability of the current titration methods. The new method provides an alternative to classical titration assays and can help reduce variation among HE vaccine products.

Structure and Sialyllactose Binding of the Carboxy-Terminal Head Domain of the Fibre from a Siadenovirus, Turkey Adenovirus 3.

The virulent form of turkey adenovirus 3 (TAdV-3), also known as turkey hemorrhagic enteritis virus (THEV), is an economically important poultry pathogen, while the avirulent form is used as a vaccine. TAdV-3 belongs to the genus Siadenovirus. The carboxy-terminal region of its fibre does not have significant sequence similarity to any other adenovirus fibre heads of known structure. Two amino acid sequence differences between virulent and avirulent TAdV-3 map on the fibre head: where virulent TAdV-3 contains Ile354 and Thr376, avirulent TAdV-3 contains Met354 and Met376. We determined the crystal structures of the trimeric virulent and avirulent TAdV-3 fibre head domains at 2.2 Å resolution. Each monomer contains a beta-sandwich, which, surprisingly, resembles reovirus fibre head more than other adenovirus fibres, although the ABCJ-GHID topology is conserved in all. A beta-hairpin insertion in the C-strand of each trimer subunit embraces its neighbouring monomer. The avirulent and virulent TAdV-3 fibre heads are identical apart from the exact orientation of the beta-hairpin insertion. In vitro, sialyllactose was identified as a ligand by glycan microarray analysis, nuclear magnetic resonance spectroscopy, and crystallography. Its dissociation constant was measured to be in the mM range by isothermal titration calorimetry. The ligand binds to the side of the fibre head, involving amino acids Glu392, Thr419, Val420, Lys421, Asn422, and Gly423 binding to the sialic acid group. It binds slightly more strongly to the avirulent form. We propose that, in vivo, the TAdV-3 fibre may bind a sialic acid-containing cell surface component.

Longitudinal field studies of Avian Metapneumovirus and Turkey Hemorrhagic Enteritis Virus in turkeys suffering from colibacillosis associated mortality

The aim of this study was to evaluate if the exposure to Avian metapneumovirus (aMPV) and/or to Turkey hemorrhagic enteritis virus (THEV) was significant for the induction of episodes of colibacillosis in aMPV and THEV vaccinated turkeys. Colibacillosis-associated mortality was recorded and longitudinal virological studies performed in three consecutive turkey flocks reared in the same farm. aMPV and THEV diagnostic swabs and blood samples were made once a week up to 14weeks of age. Swabs were processed by molecular techniques for viruses detection and antibody titres were evaluated. Field subtype B aMPVs were detected in all flocks at different ages of life always associated with respiratory signs and increase of colibacillosis-associated mortality. THEV has been consistently detected in all flocks since the 9th week of age. Vaccination with a single dose of the THEV commercial inactivated vaccine available in Italy seems does not protect the birds from the infection. Sequence comparison of the hexon protein of one of the THEV strains detected, and strains isolated worldwide, revealed high similarity between them. These results are consistent with the notion that the hexon protein, being the major antigenic component of the virus, is highly conserved between the strains. Results showed that field aMPV infection is directly correlated to colibacillosis-associated mortality. Less clear appears the role of THEV because the endemicity of aMPV makes difficult to evaluate its role in predisposing colibacillosis in absence of aMPV. It would be interesting to further investigate this issue through experimental trials in secure isolation conditions.

Full genome analysis of a novel adenovirus from the South Polar skua (Catharacta maccormicki) in Antarctica

Adenoviruses have been identified in humans and a wide range of vertebrate animals, but not previously from the polar region. Here, we report the entire 26,340-bp genome of a novel adenovirus, detected by PCR, in tissues of six of nine South Polar skuas (Catharacta maccormicki), collected in Lake King Sejong, King George Island, Antarctica, from 2007 to 2009. The DNA polymerase, penton base, hexon and fiber genes of the South Polar skua adenovirus (SPSAdV) exhibited 68.3%, 75.4%, 74.9% and 48.0% nucleotide sequence similarity with their counterparts in turkey hemorrhagic enteritis virus. Phylogenetic analysis based on the entire genome revealed that SPSAdV belonged to the genus Siadenovirus, family Adenoviridae. This is the first evidence of a novel adenovirus, SPSAdV, from a large polar seabird (family Stercorariidae) in Antarctica.

Clinical Aspects of Immunosuppression in Poultry

Chickens, turkeys, and other poultry in a production environment can be exposed to stressors and infectious diseases that impair innate and acquired immunity, erode general health and welfare, and diminish genetic and nutritional potential for efficient production. Innate immunity can be affected by stressful physiologic events related to hatching and to environmental factors during the first week of life. Exposure to environmental ammonia, foodborne mycotoxins, and suboptimal nutrition can diminish innate immunity. Infectious bursal disease (IBD), chicken infectious anemia (CIA), and Marek's disease (MD) are major infectious diseases that increase susceptibility to viral, bacterial, and parasitic diseases and interfere with acquired vaccinal immunity. A shared feature is lymphocytolytic infection capable of suppressing both humoral and cell-mediated immune functions. Enteric viral infections can be accompanied by atrophic and depleted lymphoid organs, but the immunosuppressive features are modestly characterized. Some reoviruses cause atrophy of lymphoid organs and replicate in blood monocytes. Enteric parvoviruses of chickens and turkeys merit further study for immunosuppression. Hemorrhagic enteritis of turkeys has immunosuppressive features similar to IBD. Other virulent fowl adenoviruses have immunosuppressive capabilities. Newcastle disease can damage lymphoid tissues and macrophages. Avian pneumovirus infections impair the mucociliary functions of the upper respiratory tract and augment deeper bacterial infections. Recognition of immunosuppression involves detection of specific diseases using diagnostic tests such as serology, etiologic agent detection, and pathology. Broader measurements of immunosuppression by combined noninfectious and infectious causes have not found general application. Microarray technology to detect genetic expression of immunologic mediators and receptors offers potential advances but is currently at the developmental state. Control methods for immunosuppressive diseases rely largely on minimizing stress, reducing exposure to infectious agents through biosecurity, and increasing host resistance to infectious immunosuppressive diseases by vaccination. A longer-term approach involves genetic selection for resistance to immunosuppressive diseases, which has shown promising results for MD but equivocal results for IBD and CIA.

Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus

Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus

Persistent Infection of Turkeys with an Avirulent Strain of Turkey Hemorrhagic Enteritis Virus

The Virginia avirulent strain (VAS) of turkey hemorrhagic enteritis virus (THEV), which is commonly used in live vaccines for commercial turkeys, was studied to determine characteristics of infection. It has been observed that turkeys infected with the VAS maintain protective antibody levels in excess of 20 wk postvaccination. It is theorized that this immune response is modulated by either a persistent or latent infection. A series of studies have been undertaken to determine changes in virus location and serology over time. A trial was also conducted to evaluate the effect of corticosteroid administration on viral recrudescence, and an attempt was made to isolate live virus from tissues of birds 10 wk postinfection (pi). Antibody titers were determined by enzyme-linked immunosorbent assay, and PCR was used to detect viral DNA. Histopathology was performed on formalin-fixed paraffinized tissues. Viral DNA was detected in various tissues through 15 wk pi in the presence of high antibody titers. Viral DNA was detected at 3-5 days pi in the spleens of susceptible turkeys inoculated with tissues collected from infected birds at 10 wk pi. It is unknown whether the viral DNA is associated with live virus or rather is the result of persistent maintenance of the viral genome within lymphoid/macrophage target cells. Future studies will test for viral RNA in order to confirm the presence of replicating THEV. Regardless of the actual status of the THEV DNA detected at 10-15 wk pi, it is clear that THEV does not cause a simple acute infection. The characteristics of THEV infection are identical to the nonlytic persistent infections seen in human adenoviruses, and therefore THEV may serve as a model for the study of virus-cell interactions mediating persistence.

Comparison of 12 turkey hemorrhagic enteritis virus isolates allows prediction of genetic factors affecting virulence

Turkey hemorrhagic enteritis virus (THEV) is a member of the genus Siadenovirus and causes disease in turkey poults characterized by splenomegaly, bloody diarrhoea and death. The mechanism responsible for intestinal lesion formation and mortality is not known, although there is strong evidence that it is immune-mediated. All strains of THEV are serologically indistinguishable, although there are naturally occurring avirulent strains of THEV that replicate efficiently in turkeys without the intestinal haemorrhage or mortality associated with more virulent strains. The purpose of this study was to determine which viral genes are involved in virulence. The full-length genome of an avirulent vaccine strain was sequenced and compared with the genome of a virulent field isolate from Israel that was sequenced in 1998. Comparison of the two 26.3 kb genomes revealed 49 nucleotide differences resulting in 14 putative amino acid changes within viral proteins. Sequencing of the regions surrounding the 14 missense mutations revealed variations in ORF1, E3 and the fiber (fib) knob domain in five additional strains with varying degrees of virulence. Complete sequences of these genes were determined in a total of 11 different strains of THEV. All strains had at least one missense mutation in ORF1, and all but two of the strains had one missense mutation in E3. At least one missense mutation was found in the fiber knob domain in six out of seven virulent strains. Sequence variation of ORF1, E3 and fib in strains of THEV with different phenotypes strongly indicates that these genes are the key factors affecting virulence.

A subunit vaccine against hemorrhagic enteritis adenovirus

Hemorrhagic enteritis virus (HEV) is an adenovirus that infects turkeys and causes immunosuppression and mortality. The virus used for the inactivated vaccine is extracted from spleens of infected turkeys, since its propagation in tissue cultures or embryonated eggs is unsuitable for mass production. The aim of this study was to develop a subunit vaccine based on a capsid protein of the virus. The knob protein, together with an adjacent part of the shaft domain pertaining to the fiber protein of HEV, was expressed in Escherichia coli and tested as a vaccine. Vaccination with this recombinant protein conferred protection against challenge in controlled and in floor-pen experiments. This finding suggests that the knob protein may be used as safe and efficient vaccine against hemorrhagic enteritis of turkeys. The possibility that the knob proteins of other adenoviruses may be protective and serve as vaccine is also discussed.

Haemorrhagic enteritis of turkeys and related infections of pheasants and domestic fowl: a review

Haemorrhagic enteritis (HE) of turkeys is an economically important viral disease of turkeys, not only because it causes high mortality and immunosuppression, but also due to increased slaughterhouse condemnations. The disease is characterized by haemorrhagic enteritis and necrosis of lymphoid cells and a proliferation of reticuloendothelial cells in the spleen. In marble spleen disease (MSD), in addition to splenic changes, pulmonary congestion and oedema are also seen. Whereas splenomegaly in chickens (SMC) is characterized by lesions in the spleen similar to those of HE and the pulmonary lesions of MSD. The causative agents of HE of turkeys, MSD of pheasants and SMC are serologically indistinguishable group II Aviadenoviruses. All the three viruses can be propagated in lymphoblastoid cell lines derived from Marek's disease virus induced lymphoma in turkeys viz. MDTC-RP-16 and MDTC-RP19. The infection can be diagnosed by isolation and characterization of aetiological agents, serological tests such as the agar gel precipitation test, enzyme linked immunosorbent assay and the use of immunoperoxidase to demonstrate intranuclear adenovirus-like particles in infected cells shown by electron microscopy. The control of HE is possible by vaccination using avirulent MSD virus of pheasants as well as avirulent or attenuated strains of turkey HE virus.

Spleno‐enteritis caused by adenovirus in psittacine birds: A pathological study

Psittacine birds with haemorrhagic enteritis were submitted for pathological study. Histopathological examination revealed haemorrhagic enteritis and necrotic areas in the spleen, with amphophilic and basophilic intranuclear inclusion bodies in mononuclear cells of the spleen, intestinal cell infiltrate, endothelial cells of small vessels in spleen, intestine, lung and liver, and in a few hepatocytes. Thrombi were observed in intestinal capillaries. The clinical and pathological features of this outbreak resembled haemorrhagic enteritis of turkeys and immunohistochemical staining showed positive immunoreaction to group II avian adenovirus antigens in the intranuclear inclusion bodies. The possible relationship between the virus replication in endothelial cells and intestinal haemorrhages in avian adenovirus infection is discussed. This outbreak could represent a new pathological process in psittacine birds.

Molecular Detection of Infectious Bursal Disease Virus by Polymerase Chain Reaction

The polymerase chain reaction (PCR) technique was applied to the detection of infectious bursal disease virus (IBDV). Reverse transcription followed by the PCR was used to amplify a portion of IBDV genome. A set of primers that specify a 150-base-pair segment of IBDV genome was chosen from an Australian strain of IBDV. Standard challenge strain and variant strains A, D, E, G, and GLS-5 of IBDV serotype 1 and OH strain of serotype 2 from infected bursae were subjected to reverse transcription, followed by 30 cycles of PCR. A single band of the PCR product (DNA) of the expected size from each strain of IBDV was visible on polyacrylamide gels stained with ethidium bromide. Using the same primers, no PCR product was detected from genomic nucleic acids of turkey hemorrhagic enteritis virus, infectious bronchitis virus, reovirus, Salmonella enteritidis, Escherichia coli, and uninfected bursae. The PCR could be efficiently performed on serially diluted IBDV RNA and could detect 2 femtograms of IBDV RNA. The identity of the PCR products was confirmed by direct sequencing. The PCR is a specific and sensitive method for the detection of IBDV.

Hemorrhagic enteritis of turkeys

Hemorrhagic enteritis (HE), an economically important disease of turkeys is caused by a type II adenovirus. The virus is ubiquitous and is liable to infect most field turkeys. In unprotected turkey flocks, infection with virulent hemorrhagic enteritis virus (HEV) may result in variable mortality and immunodepression. Turkeys younger than 2–4 weeks of age are resistant to clinical HE. This age-related resistance is expressed in the presence or absence of maternal antibodies against HEV. Clinical disease is characterized by HE and splenomegaly. The virus causes intranuclear inclusions in the reticuloendothelial cells. Bursectomy or splenectomy abrogate clinical HE. Field data and laboratory studies indicate that HEV causes immunodepression in the humoral as well as the cellular immune functions of turkeys. The mechanism of immunodepression is not known.