Pathogenesis of type II avian adenovirus infection in turkeys: in vivo immune cell tropism and tissue distribution of the virus

Effect of Immunomodulation in Turkeys Infected with Haemorrhagic Enteritis Virus on the Percentage of CD4+ and CD8α+ T Lymphocyte Subpopulations Synthesising IFN-γ

Introduction

Haemorrhagic enteritis virus (HEV) is a common turkey pathogen which suppresses the immune function. The immunosuppressive potential of both field and vaccine strains of HEV makes it necessary to seek substances which can limit or prevent this phenomenon. The aim of the presented work was to investigate the effect of two immunomodulators in the immune response of HEV-infected turkeys. The immunomodulators were synthetic methisoprinol and a natural preparation containing 34.2% β-glucans (β-1,3/1,6) and 12% mannan oligosaccharides (MOS).

Material and Methods

The synthetic immunomodulator was administered to female Big 6 turkey chicks at a dose of 200 mg/kg b.w. in drinking water i) for 3 days before, ii) for 5 days after, or iii) for 3 days before, on the day of infection, and for 5 days after experimental HEV infection in turkeys. The natural counterpart was also given to female Big 6 turkey chicks at a dose of 500 g/tonne of feed i) for 14 days before, ii) for 5 days after, or iii) for 14 days before, on the day of infection, and for 5 days after infection. Their effect was evaluated on the synthesis of interferon gamma (IFN-γ) by splenic CD4+ and CD8α+ T cells in response to mitogen stimulation in vitro. Samples were taken 3, 5 and 7 days after infection and analysed by intracellular cytokine staining assay.

Results

Methisoprinol was shown to increase the CD4⁺IFN-γ⁺ and CD8α⁺IFN-γ⁺ T cell count in these birds over the same cell count in control turkeys. A similar effect was obtained in turkeys that received the natural immunomodulator.

Conclusion

The evaluated immunomodulators may be used to attenuate the effects of immunosuppression in HEV-infected turkeys.

Turkey adenovirus 3, a siadenovirus, uses sialic acid on N-linked glycoproteins as a cellular receptor

Turkey adenovirus 3 (TAdV-3) is the causative agent of an immune-mediated disease in turkeys, haemorrhagic enteritis, through targeting B lymphocytes. In the present study, we investigated the role of sialic acid in TAdV-3 entry and characterized the structural components of TAdV-3 receptor(s) on RP19, B lymphoblastoid cells. Removal of the cell-surface sialic acids by neuraminidases or blocking of sialic acids by wheat germ agglutinin lectin reduced virus infection. Pre-incubation of cells with Maackia amurensis lectin or Sambucus nigra agglutinin resulted in virus reduction, suggesting that TAdV-3 uses both α2,3-linked and α2,6-linked sialic acids as attachment receptor. Virus infectivity data from RP19 cells treated with sodium periodate, proteases (trypsin or bromelain) or metabolic inhibitors (dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, tunicamycin, or benzyl N-acetyl-α-d-galactosaminide) indicated that N-linked, but not O-linked, carbohydrates are part of the sialylated receptor and they are likely based on a membrane glycoprotein, rather than a glycolipid. Furthermore, our data, in conjunction with previous findings, implies that the secondary receptor for TAdV-3 is a protein molecule since the inhibition of glycolipid biosynthesis did not affect the virus infection, which was rather reduced by protease treatment. We can conclude that terminal sialic acids attached to N-linked membrane glycoproteins on B cells are used for virus attachment and are essential for successful virus infection.

Microbiota in viral infection and disease in humans and farm animals

The influence of the microbiota on viral infection susceptibility and disease outcome is undisputable although varies among viruses. The purpose of understanding the interactions between microbiota, virus, and host is to identify practical, effective, and safe approaches that target microbiota for the prevention and treatment of viral diseases in humans and animals, as currently there are few effective and reliable antiviral therapies available. The initial step for achieving this goal is to gather clinical evidences, focusing on the viral pathogens-from human and animal studies-that have already been shown to interact with microbiota. The subsequent step is to identify mechanisms, through experimental evidences, to support the development of translational applications that target microbiota. In this chapter, we review evidences of virus infections altering microbiota and of microbiota enhancing or suppressing infectivity, altering host susceptibility to certain viral diseases, and influencing vaccine immunogenicity in humans and farm animals.

Virus-induced immunosuppression in turkeys (Meleagris gallopavo): A review

Immunosuppression is characterized by a dysfunction of humoral and/or cellular immune response leading to increase of susceptibility to secondary infections, increase of mortality and morbidity, poor productivity, and welfare and vaccination failures. Humoral immune response depression is due to perturbation of soluble factors, as complement and chemokines in innate immunity and antibodies or cytokines in adaptive immunity. At the cellular immune response, immunosuppression is the consequence of the dysfunction of T-cells, B-cells, heterophils, monocytes, macrophages, and natural Killer cells. Immunosuppression in turkeys can be caused by numerous, non-infectious, and infectious agents, having variable pathological and molecular mechanisms. Interactions between them are very complex. This paper reviews the common viruses inducing clinical and sub-clinical immunosuppression in turkeys, and enteric and neoplastic viruses in particular, as well as the interactions among them. The evaluation of immunosuppression is currently based on classical approach; however, new technique such as the microarray technology is being developed to investigate immunological mediator’s genes detection. Controlling of immunosuppression include, in general, biosecurity practices, maintaining appropriate breeding conditions and vaccination of breeders and their progeny. Nevertheless, few vaccines are available against immunosuppressive viruses in turkey’s industry. The development of new control strategies is reviewed.

The immune response of young turkeys to haemorrhagic enteritis virus infection at different levels and sources of methionine in the diet

Background

Haemorrhagic enteritis (HE) of turkeys was first described in 1937 in the USA, while in Poland it was first diagnosed in 1987. Polish haemorrhagic enteritis virus (HEV) isolates are usually low pathogenic and trigger a subclinical disease. Unfortunately, even the low- pathogenic HEV strains cause severe immunosuppression leading to secondary bacterial infections and huge economic losses. The objective of this study was to evaluate if the influence of Met on HEV infected turkeys immune response can be differentiated by both its level and source. Met is one of the amino acids that not only play a nutritional role but also participate in and regulate key metabolic pathways and immune response. In our study, the birds were assigned to 4 dietary treatments which differed in Met levels (0.55 and 0.78% in weeks 1–4 of age and 0.45 and 0.65% in weeks 5–8 of age, respectively) and sources (DL-methionine (DLM) or DL-methionine hydroxy analogue (MHA)).

Results

The HEV added the percentage of CD4⁺ cells and decreased the percentage of IgM⁺ cells in the blood, spleen and caecal tonsils (CTs) of turkeys. In addition, it increased the percentage of CD4⁺CD25⁺ cells in blood, and interleukin-6 (IL-6) level in plasma. The higher dose of Met led to a significant decrease in the percentages of CD4⁺, CD8⁺ and CD4⁺IL-6⁺ cell subpopulations in the blood of HEV-infected and uninfected turkeys and to an increase in the percentage of IgM⁺ B cells in CTs. Turkeys administered feeds with an increased Met content displayed a decrease in plasma IL-6 levels and an increase in plasma IgA levels.

Conclusions

The results of this study indicate that HEV infection impairs the immune function in turkeys. Met content in the feed has a moderate effect on the immune response in HEV-infected turkeys. The source of this amino acid appears not be as important as its dose, because value of the analysed parameters did not differ significantly between turkeys receiving feeds with DLM or MHA. In the uninfected turkeys, the higher by 40% (than recommended by NRC) level of Met in the feeds had a positive effect on humoral immunity parameters.

Changes in the intestinal mucosal proteome of turkeys (Meleagris gallopavo) infected with haemorrhagic enteritis virus

Haemorrhagic enteritis (HE) is a viral disease affecting intestinal integrity and barrier function in turkey (Meleagris gallopavo) and resulting in a significant economic loss. Sequential Windowed Acquisition of All Theoretical Fragment Ion Mass Spectra (SWATH-MS) was applied to identify crucial proteins involved in HE infection. A total of 938 proteins were identified and used to generate a reference library for SWATH-MS analysis. In total, 523 proteins were reliably quantified, and 64 proteins were found to be differentially expressed, including 49 up-regulated and 15 down-regulated proteins between healthy and HE-affected intestinal mucosa. Functional analysis suggested that these proteins were involved in the following categories of cellular pathways and metabolisms: 1) energy pathways; 2) intestine lipid and amino acid metabolism; 3) oxidative stress; 4) intestinal immune response. Major findings of this study demonstrated that natural HE infection is related to the changes in abundance of several proteins involved in cell-intrinsic immune defense against viral invasion, systemic inflammation, modulation of excessive inflammation, B and T cell development and function and antigen presentation. mRNA quantitative expression demonstrated that most of the proteins involved in innate immunity that were found to be differentially abundant were produced by intestinal mucosa, suggesting its direct involvement in immune defences against HE infection.

In vitro growth kinetics and gene expression analysis of the turkey adenovirus 3, a siadenovirus

Turkey adenovirus 3 (TAdV-3) belongs to the genus Siadenovirus, family Adenoviridae. Previously, nucleotide sequencing and annotation of the Virginia avirulent strain (VAS) of TAdV-3 genome, isolated in our laboratory, indicated the presence of a total of 23 genes and open reading frames (ORFs). The goals of this study were 1) to delineate the growth kinetics of the virus using a qPCR-based infectivity assay, and 2) to determine the virus gene expression profile during the early and late phases of infection in target B lymphocytes. The one-step growth curve experiment demonstrated 3 phases of virus replication cycle: a lag phase lasted for 12-18 h post-infection (h.p.i.), in which the virus titer declined; a log phase from 18 to 120 h.p.i., in which the number of infectious virus particles increased over 20,000 folds, and a brief decline phase thereafter. Southern blot analysis indicated that the synthesis of new viral DNA started by 8 h.p.i. Gene-specific RT-PCR analysis revealed the expression of mRNAs from the 23 TAdV-3 genes/ORFs. According to the temporal transcriptional profiling of TAdV-3 genome, genes could be divided into 3 groups based on the time of transcription initiation: group 1 showed detectable levels of transcription at 2 h.p.i and included 7 genes, i.e., hyd, III, pX, pVI, II, 100 K, and 33 K; group 2 included 12 genes whose mRNAs were detected for the first time at 4 h.p.i., i.e., ORF1, IVa2, pol, pTP, pIIIa, EP, DBP, E3, U exon, IV, ORF7, and ORF8; group 3 of transcripts were detectable starting 8 h.p.i. and included only 4 genes, i.e., 52 K, 22 K, pVII, and pVIII. Our data suggest that the transcriptional kinetics of genus Siadenovirus differ from that observed in other adenoviral genera; however, a few TAdV-3 genes showed similar expression patterns to their adenoviral homologs.

Gastrointestinal microbial population of turkey (Meleagris gallopavo) affected by hemorrhagic enteritis virus

Hemorrhagic enteritis (HE) is an acute viral disease that affects avian species, particularly turkeys, compromising their commercial production and having a negative effect on animal welfare. Turkey adenovirus 3 (TAdV-3), is the main causal agent of the disease. In this study, we considered 3 groups of turkeys to achieve 2 purposes: 1) A preliminary investigation on the microbiota content in the 4 parts of healthy turkey's intestine (group A), namely duodenum, jejunum, ileum, and ceca was done; 2) an investigation on the relationship between natural infections with TAdV-3 and the intestinal microbiota in the jejunum, where HE mostly develops, comparing group A with animals with molecular positivity for the virus and with clinical signs of HE (group B) and animals with molecular positivity for the virus but without clinical signs (group C). Massive sequencing of the hypervariable V1-V2 regions of 16S rRNA gene and QIIME 1.9.1 software analysis was performed, and operation taxonomic units (OTUs) were classified into 4 abundant phyla: Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. The microbial population of small intestine was distributed almost homogeneously in the healthy turkeys, and Firmicutes was the prevalent phylum (79.85% in duodenum, 89.57% in jejunum and 99.28% in ileum). As compared with small intestine, ceca microbial community was much more heterogeneous: Firmicutes (48.03%), Bacteroidetes (33.60%) and Proteobacteria (12.32%). In the natural infections of HEV, the main bacterial families were Bacteroidaceae (Bacteroidetes) and Peptostreptococcaceae (Firmicutes), uniquely detected in group B and C. Also Clostridiaceae (Firmicutes) was detected, uniquely in group B.

Haemorrhagic enteritis of turkeys - current knowledge

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.

Molecular Characterization of Hemorrhagic Enteritis Viruses (HEV) Detected in HEV-Vaccinated Commercial Turkey Flocks in Germany

Despite the application of live hemorrhagic enteritis virus (HEV) vaccines, HEV field outbreaks are suspected to still occur in turkey flocks in Germany. Increasing secondary bacterial infections in HEV-vaccinated flocks suggest that vaccines may be losing efficacy or, possibly, that vaccine strains are causing disease. Thus, the goal of the current study was to investigate the diversity of HEV isolates from fattening turkey flocks between 2008 and 2012 by characterizing the open reading frame (ORF)1 gene at its 5' and 3' ends. Analyses of ORF1 sequences of field isolates and comparison with sequences present in databases revealed that in many cases (13 out of 16 samples), vaccine (avirulent) strains were present. In addition, data indicated the circulation of suspected virulent field isolates and these isolates (3 out of 16) cluster with an early isolate from Germany in the 1980s, but show some mutations in the predicted amino acid (aa) sequences of ORF1 compared to the early isolate. These virulent isolates clearly differ from the spleen-derived avirulent Domermuth vaccine strain used in Germany. In this study, a unique isolate was identified and showed unusual nucleotide mutations that resulted in aa exchanges at the 5' end of ORF1 between aa positions 34 and 174. This genetic drift suggests evolution of HEV including virulent and vaccine-derived strains in the field. This may lead to evasion of vaccinal immunity by drifted viruses and/or an increase in the virulence of field strains.

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.

Expression and serological reactivity of hemorrhagic enteritis virus hexon protein

The aim of this work was to express the recombinant hexon protein of the hemorrhagic enteritis virus, to establish the diagnostic value of this protein for serological detection of antibodies in turkey serum samples and to assess seroprevalence of the infection in the Czech Republic. The N' terminal part of the hexon protein was expressed in a bacterial expression system and used as an antigen in an ELISA test for the detection of hemorrhagic enteritis virus specific antibodies in turkey sera. Validation of the test was performed by comparison with a commercially available ELISA test. Serological reactivity was assessed on a panel of 126 turkey sera by a newly developed ELISA test. Serum samples were taken from turkey farms with the history of hemorrhagic enteritis virus infection, from farms with animals free of infection, and from turkey farms following vaccination. Both ELISA kits gave identical results (100 %) with the tested sera. ELISA based on the recombinant hexon protein thus proved useful and cheaper for detection of antibodies in turkey flocks infected with the hemorrhagic enteritis virus.

Development and application of quantitative real-time PCR for the rapid detection of hemorrhagic enteritis virus in tissue samples

Hemorrhagic enteritis virus (HEV) is a type II avian adenovirus that causes intestinal hemorrhages accompanied with immunosuppression in 4-to-12-wk-old turkeys. In the present study, a hexon gene-based, quantitative real-time PCR with TaqMan probe was developed and applied to tissue samples from poultry farms to detect and quantify HEV genome copy numbers. The method was confirmed to be rapid, specific, and sensitive for the detection of HEV. This method is an excellent research and diagnostic tool that can be used to study pathogenesis and to gain insights into different phases of infection on poultry farms and for high-throughput epidemiologic investigations.

Effect of infection of turkeys with haemorrhagic enteritis adenovirus isolate on the selected parameters of cellular immunity and the course of colibacillosis

The aim of the study was to determine the effect of a Polish low-virulence isolate of haemorrhagic enteritis adenovirus (HEV) on the immune system in turkeys and on the course of colibacillosis in birds infected under laboratory conditions. Turkeys were infected per os with HEV at the dose of 10(4.3)EID50/mL and with E. coli (APEC) (serotypes 078:K80:H9) at the dose of 4x10(9)CFU/mL by injection to the thoracic air sac. The birds infected with the HEV were infected with the APEC either simultaneously or after 5 days. Five days after HEV infection, the percentages of subpopulations of the CD3+CD4+ and CD3+CD8alpha+ T cells and the IgM+ B cells were determined in blood and spleens of the HEV-infected turkeys and in the control (uninfected) birds. The course of colibacillosis was more severe in turkeys infected with the APEC 5 days after infection with the HEV than in those infected with the HEV and APEC simultaneously and than in those infected only with APEC. Five turkeys out of the 18 infected with the APEC 5 days after infection with HEV, died. Their body weights were statistically significantly lower with higher FCR values 41 days after the infection in comparison to turkeys in the other groups. A considerable decrease in the percentage of the T and B cells subpopulations in the blood were found in turkeys infected with the HEV and while the percentage of CD3+CD4+ T cells subpopulation in the spleen increased significantly, the contribution of the CD3+CD8alpha+ T cells and IgM+ B cells subpopulations were decreased. These changes in the immune system of turkeys, occurring 5 days after infection with the HEV, made them more susceptible to infection with the APEC.

Experimental reproduction of poult enteritis syndrome: clinical findings, growth response, and microbiology

Poult enteritis syndrome (PES) is an infectious disease of turkey poults characterized by diarrhea, dullness, and depression. Five experiments were conducted to reproduce the disease in turkey poults using intestinal contents of PES-affected birds. In all experiments, poults at 14 d of age were divided into 4 groups and were orally given 2 mL of unfiltered supernatant, filtered supernatant, sediment dissolved in PBS, or PBS alone. Inocula in experiments 1, 3, and 5 consisted of intestinal contents from PES-affected birds of less than 2 wk of age, whereas those in experiments 2 and 4 consisted of intestinal contents from PES-affected birds of 4 to 6 wk of age. Poults in all groups were observed daily for clinical signs. The BW and microbiological criteria in experiments 1, 3, and 5 were evaluated at 5, 10, and 15 d postinoculation, whereas in experiments 2 and 4, these observations were made at 10 and 20 d postinoculation. Rotavirus, astrovirus, and Salmonella were present in all 5 inocula. Diarrhea and depression were the major signs in poults given PES material. Significant retardation of growth was observed in poults given any of the 3 PES materials, but this effect was more pronounced in poults given the sediment inoculum. Rotavirus, astrovirus, and Salmonella were detected in poults given PES material. In some cases, enterovirus was also detected. No major difference was noticed in experimental reproduction of PES when intestinal contents from different age birds were used as the inoculum.

Immunohistochemical detection and localization of new type gosling viral enteritis virus in paraformaldehyde-fixed paraffin-embedded tissue

To determine the distribution and localization of new type gosling viral enteritis virus (NGVEV) in paraformaldehyde-fixed paraffin-embedded tissues of experimentally infected goslings, for the first time, an immunohistochemical (IHC) staining method was reported. Anti-NGVEV polyclonal serum was obtained from the rabbits immunized with purified NGVEV antigen, which was extracted by caprylic-ammonium sulphate method and purified through High-Q columns anion exchange chromatography. Three-day-old NGVEV-free goslings were orally inoculated with NGVEV-CN strain suspension as infection group and phosphate buffered saline solution (PBS) as control group, respectively. The tissues were collected at sequential time points between 0.5 and 720h post inoculation (PI), and prepared for IHC staining and ultra-structural observation. The positive immunoreactivity could be readily detected in the lymphoid and gastrointestinal organs of infected goslings as early as 48 h PI, in the liver, kidney, pancreas and myocardium from 72 h, and in the cerebrum and cerebellum from 96 h, while it was hardly detected in the respiratory organs at any time. The positive staining reaction could be detected in NGVEV-infected goslings until 600 h PI, and no positive staining cell could be observed in the controls. The highest levels of viral antigen were found in the bursa of Fabricius (BF), thymus, proventriculus, gizzard and intestine tract, moreover, the liver, kidney, spleen, myocardium and pancreas were intensively and widely stained. The target cells had a ubiquitous distribution, especially included the epithelial cells, endothelial cells, superficial and crypt mucosal cells, glandular cells, fibrocytes, macrophages and lymphocytes, which served as the principal sites for antigen localization. The ultra-structural observation by transmission electron microscope (TEM) further indicated that NGVEV particles could be widely detected in the lymphoid and digestive organs of infected goslings from 72 h PI onwards. This work may be useful not only for offering a possibility of routine diagnosis of NGVE, but also for better understanding of the pathogenesis of the disease.

Enteric viruses detected by molecular methods in commercial chicken and turkey flocks in the United States between 2005 and 2006

Intestinal samples collected from 43 commercial broiler and 33 commercial turkey flocks from all regions of the United States during 2005 and 2006 were examined for the presence of astrovirus, rotavirus, reovirus, and coronavirus by reverse transcription-polymerase chain reaction (PCR), and for the presence of groups 1 and 2 adenovirus by PCR. Phylogenetic analysis was performed to further characterize the viruses and to evaluate species association and geographic patterns. Astroviruses were identified in samples from 86% of the chicken flocks and from 100% of the turkey flocks. Both chicken astrovirus and avian nephritis virus (ANV) were identified in chicken samples, and often both viruses were detected in the same flock. Turkey astrovirus type-2 and turkey astrovirus type-1 were found in 100% and 15.4% of the turkey flocks, respectively. In addition, 12.5% of turkey flocks were positive for ANV. Rotaviruses were present in 46.5% of the chicken flocks tested and in 69.7% of the turkey flocks tested. Based upon the rotavirus NSP4 gene sequence, the chicken and turkey origin rotaviruses assorted in a species-specific manner. The turkey origin rotaviruses also assorted based upon geographical location. Reoviruses were identified in 62.8% and 45.5% of chicken and turkey flocks, respectively. Based on the reovirus S4 gene segment, the chicken and turkey origin viruses assorted separately, and they were distinct from all previously reported avian reoviruses. Coronaviruses were detected in the intestinal contents of chickens, but not turkeys. Adenoviruses were not detected in any chicken or turkeys flocks. Of the 76 total chicken and turkey flocks tested, only three chicken flocks were negative for all viruses targeted by this study. Most flocks were positive for two or more of the viruses, and overall no clear pattern of virus geographic distribution was evident. This study provides updated enteric virus prevalence data for the United States using molecular methods, and it reinforces that enteric viruses are widespread in poultry throughout the United States, although the clinical importance of most of these viruses remains unclear.

Periodic monitoring of commercial turkeys for enteric viruses indicates continuous presence of astrovirus and rotavirus on the farms

A longitudinal survey to detect enteric viruses in intestinal contents collected from turkeys in eight commercial operations and one research facility was performed using molecular detection methods. Intestinal contents were collected from turkeys prior to placement, with each flock resampled at 2, 4, 6, 8, 10, and 12 wk of age. The samples were screened for astrovirus, rotavirus, reovirus, and turkey coronavirus (TCoV) by a reverse transcriptase and polymerase chain reaction (RT-PCR), and for groups 1 and 2 adenovirus by PCR. Rotavirus was the only virus detected prior to placement (7 of 16 samples examined). All of the commercial flocks were positive for rotavirus and astrovirus from 2 until 6 wk of age, and most were intermittently positive until 12 wk of age, when the birds were processed. Of the 96 samples collected from birds on the farms, 89.5% were positive for astrovirus, and 67.7% were positive for rotavirus. All flocks were negative for TCoV, reovirus, and group 1 adenovirus at all time points, and positive for group 2 adenovirus (hemorrhagic enteritis virus) at 6 wk of age. All the flocks monitored were considered healthy or normal by field personnel. Turkeys placed on research facilities that had been empty for months and thoroughly cleaned had higher body weights and lower feed conversion rates at 5 wk of age when compared to turkeys placed on commercial farms. Intestinal samples collected at 1, 2, and 3 wk of age from these turkeys were free of enteric viruses. This report demonstrates that astroviruses and rotaviruses may be present within a turkey flock through the life of the flock. Comparison of infected birds with one group of turkeys that were negative for enteric viruses by the methods used here suggests that astrovirus and/or rotavirus may affect production. The full impact on flock performance needs to be further determined.

Partial characterization of an adenovirus-like virus isolated from broiler chickens with transmissible viral proventriculitis

Transmissible viral proventriculitis (TVP) was experimentally reproduced in specific-pathogen-free chickens using a homogenate of proventricular tissue obtained from TVP-affected commercial broiler chickens. Thin-section electron microscopy revealed intranuclear, approximately 70-nanometer (nm), adenovirus-like viruses (AdLV) within proventricular lesions. The AdLV, designated AdLV (R11/3), could not be propagated using various avian and mammalian cell cultures or by inoculation of embryonated chicken eggs by yolk, allantoic, or chorioallantoic membrane routes. However, AdLV (R11/3) was successfully propagated by amniotic inoculation of embryonated chicken eggs, with detection of the virus in proventriculi and intestinal contents of hatched 2-day-old chicks (8 days postinoculation). Virus propagation was evident in in ovo-inoculated chicks by (1) gross and microscopic lesions in proventriculi consistent with TVP, (2) immunohistochemical localization of AdLV (R11/3) antigens in proventricular epithelium, (3) thin-section electron microscopic detection of intranuclear, approximately 70-nm AdLVs within proventricular epithelium, and (4) negative-stain electron microscopic detection of extracellular, approximately 70-nm AdLVs in intestinal contents. Indirect immunofluorescence and polymerase chain reaction procedures that specifically recognize groups I, II, and III avian adenoviruses failed to recognize AdLV (R11/3). The findings suggest an etiologic role for AdLV (R11/3) in TVP and indicate that this virus is distinct from known avian adenoviruses.

Characterization of a new species of adenovirus in falcons

In 1996, a disease outbreak occurred at a captive breeding facility in Idaho, causing anorexia, dehydration, and diarrhea or sudden death in 72 of 110 Northern aplomado falcons (Falco femoralis septentrionalis) from 9 to 35 days of age and in 6 of 102 peregrine falcons (Falco peregrinus) from 14 to 25 days of age. Sixty-two Northern aplomado and six peregrine falcons died. Epidemiologic analyses indicated a point source epizootic, horizontal transmission, and increased relative risk associated with cross-species brooding of eggs. Primary lesions in affected birds were inclusion body hepatitis, splenomegaly, and enteritis. The etiology in all mortalities was determined by molecular analyses to be a new species of adenovirus distantly related to the group I avian viruses, serotypes 1 and 4, Aviadenovirus. In situ hybridization and PCR demonstrated that the virus was epitheliotropic and lymphotropic and that infection was systemic in the majority of animals. Adeno-associated virus was also detected by PCR in most affected falcons, but no other infectious agents or predisposing factors were found in any birds. Subsequent to the 1996 epizootic, a similar disease caused by the same adenovirus was found over a 5-year period in orange-breasted falcons (Falco deiroleucus), teita falcons (Falco fasciinucha), a merlin (Falco columbarius), a Vanuatu peregrine falcon (Falco peregrinus nesiotes), and gyrfalcon x peregrine falcon hybrids (Falco rusticolus/peregrinus) that died in Wyoming, Oklahoma, Minnesota, and California. These findings indicate that this newly recognized adenovirus is widespread in western and midwestern North America and can be a primary pathogen in different falcon species.

Immunopathogenesis of haemorrhagic enteritis virus (HEV) in turkeys

Infection of turkeys with the haemorrhagic enteritis virus (HEV), a type II avian adenovirus, results in varying rates of morbidity and mortality. The disease is characterised by splenomegaly, intestinal haemorrhage, sudden death and immunosuppression. The mechanisms of HEV immunopathogenesis and immunosuppression are not fully understood. Recent studies indicate that immune responses play a central role in disease pathogenesis. HEV infects B cells and macrophages and induces necrosis as well as apoptosis in infected and possibly in by-stander cells. The ability of the infected birds to mount an optimum humoral immune response as well as normal macrophage functions such as phagocytosis may be impaired. Elevated numbers of splenic CD4(+) cells during the acute phase of infection may be associated with viral clearance. Types I and II interferons (IFN) and pro-inflammatory cytokines such as interleukin-6 and tumour necrosis-like factors (TNF) are released at the peak of the infection. Cytokines may play a protective as well as a destructive role. While a massive release of proinflammatory cytokines may lead to systemic shock associated with haemorrhagic enteritis and death, release of IFNs may protect turkeys from the disease. Treatment with thalidomide, which is a potent TNF down-regulatory drug, prevented HEV-induced intestinal haemorrhage and treatment with an IFN-inducing chemical prevented HEV-replication and inhibited HEV-induced pathological and histopathological lesions.

PCR for specific detection of haemorrhagic enteritis virus of turkeys, an avian adenovirus

A hexon gene based PCR was developed for specific amplification of DNA sequences from the haemorrhagic enteritis virus (HEV) of turkeys. The hexon genes of different avian adenoviruses were compared for primer construction. Two regions with low sequence homology between HEV and fowl adenovirus (FAV) hexon genes were selected for primer localisation. In correlation with the known sequence data a fragment of 1647 bp was amplified from a live vaccine and spleens of turkeys suffering from haemorrhagic enteritis (HE). All other avian adenoviruses which are able to infect turkeys, i.e. FAV and turkey adenoviruses (TAV), were negative. This is the first PCR for specific detection of HEV DNA which should be useful for rapid diagnosis and epidemiological investigations of HEV infections in turkeys.

Comparative pathogenesis of haemorrhagic enteritis virus (HEV) infection in turkeys and chickens

The pathogenesis of haemorrhagic enteritis virus (HEV) infection in chickens 3-4 days post-infection was compared with that in turkeys. As expected, infected turkeys showed HEV-specific lesions that included enlargement and mottling of the spleen, as well as haemorrhagic enteritis. In infected chickens, only splenomegaly was observed. The number of HEV-infected cells in the spleen was significantly (P < 0.05) higher in the turkey than in the chicken. In both species, the immunohistochemical labelling of B-cell surface determinants was diminished and the splenic B-cell areas were undetectable after HEV infection. Infection with HEV resulted in an increase in nitric oxide production by macrophages in chickens but not in turkeys.

The complete DNA sequence and genome organization of the avian adenovirus, hemorrhagic enteritis virus

Hemorrhagic enteritis virus (HEV) belongs to the Adenoviridae family, a subgroup of adenoviruses (Ads) that infect avian species. In this article, the complete DNA sequence and the genome organization of the virus are described. The full-length of the genome was found to be 26,263 bp, shorter than the DNA of any other Ad described so far. The G + C content of the genome is 34.93%. There are short terminal repeats (39 bp), as described for other Ads. Genes were identified by comparison of the DNA and predicted amino acid sequences with published sequences of other Ads. The organization of the genome in respect to late genes (52K, IIIa, penton base, core protein, hexon, endopeptidase, 100K, pVIII, and fiber), early region 2 genes (polymerase, terminal protein, and DNA binding protein), and intermediate gene IVa2 was found to be similar to that of other human and avian Ad genomes. No sequences similar to E1 and E4 regions were found. Very low similarity to ovine E3 region was found. Open reading frames were identified with no similarity to any published Ad sequence.

Distribution of mouse adenovirus type 1 in intraperitoneally and intranasally infected adult outbred mice

In situ nucleic acid hybridization and immunohistochemistry were used to determine the histological localization of mouse adenovirus type 1 (MAV-1) during acute infection of adult mice infected either intraperitoneally or intranasally with 1,000 PFU of wild-type virus. Organ samples were collected from days 1 to 17 postinfection for the intraperitoneally infected mice and from days 1 to 13 for the intranasally infected mice. Endothelial cells of the brain and spinal cord showed extensive evidence of MAV-1 infection. Endothelial cells in lungs, kidneys, and other organs were also positive for MAV-1, indicating a widespread involvement of the systemic circulation. The presence of viral nucleic acid and/or antigen was also demonstrated in lymphoid tissue. The spleens, Peyer's patches, and peripheral lymph nodes showed positive staining at various times postinfection in mice infected by either route. Virus-infected cells in the spleen exhibited a stellate shape and were localized to the red pulp and germinal centers, suggesting that they are cells of the mononuclear phagocytic system.