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

The impact of full-fat Hermetia illucens larvae meal on the health and immune system function of broiler chickens

Introduction

Alternative protein sources have recently been attracting growing interest as potential components of livestock nutrition. This study evaluated the effect on broiler health of replacing the soybean protein component of poultry feed with processed insect protein from farmed Hermetia illucens (HI) larvae.

Material and Methods

A total of 384 male broiler chicks were divided into four diet groups (eight pens/treatment and 12 birds/pen) and reared to the 42nd day of life (dol). Each treatment group received a starter diet until the 14th dol, then a grower diet until the 35th and finally a finisher diet until the 42nd. The soybean meal in standard diets was replaced with full-fat HI larvae meal in the following amounts: 0% for the control group HI-0, 50% for group HI-50, 75% for group HI-75, and 100% for group HI-100. At 1 dol, chicks were vaccinated against Marek's disease, coccidiosis, Newcastle disease and infectious bronchitis and at 7 dol against avian metapneumovirus infections using live-attenuated vaccines. Blood and spleen samples were collected at three and six weeks of age and analysed using ELISA, flow cytometry, haematology and biochemistry.

Results

On the 42nd dol, as the content of larvae meal in the chickens' diets increased, the birds' body weights decreased significantly. The substitution of the protein source had no effect on the haematological markers. In chicks that received larvae meal, there was a decrease in creatine kinase activity and phosphorus levels and an increase in calcium and uric acid levels in serum. Raising the proportion of full-fat HI larvae meal in the diet raised the percentage of T CD3+CD8a+ cells and lowered that of T CD3+CD4+ cells in both sample types. Chickens fed larvae meal had significantly lower post-vaccination anti-infectious bronchitis virus antibody titres.

Conclusion

The poorer production results and impaired health in experimental birds may indicate lower than 50% protein substitution with full-fat HI larvae meal to be optimal.

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.

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.

Increased arginine, lysine, and methionine levels can improve the performance, gut integrity and immune status of turkeys but the effect is interactive and depends on challenge conditions

Arginine (Arg), lysine (Lys), and methionine (Met) can be used to support the health status of turkeys. The present study investigated selected performance, gut integrity, and immunological parameters in turkeys reared in optimal or challenge conditions. The experiment lasted for 28 days, and it had a completely randomized 2 × 3 factorial design with two levels of dietary Arg, Lys and Met (high or low) and challenge with Clostridium perfringens (C. perfringens), Escherichia coli lipopolysaccharide (LPS) or no challenge (placebo). Increased dietary levels of Arg, Lys and Met had a beneficial effect on turkey performance and immunological parameters, and it improved selected indicators responsible for maintaining gut integrity in different challenge conditions. Under optimal conditions (with no challenge), high ArgLysMet diets did not compromise bird performance and they improved selected performance parameters in challenged birds. The immune system of turkeys was not excessively stimulated by high ArgLysMet diets, which did not disrupt the redox balance and had no negative effect on gut integrity. High ArgLysMet diets increased the expression levels of selected genes encoding nutrient transporters and tight junction proteins. However, the influence exerted by different dietary inclusion levels of Arg, Lys and Met on gut integrity was largely determined by the stressor (C. perfringens vs. LPS). Further studies are required to investigate the role of Arg, Lys and Met levels in the diet on the immune response, gut function and performance of turkeys in different challenge conditions.

Immune Parameters in Chickens Treated with Antibiotics and Probiotics during Early Life

The aim of the study was to compare the effect of the administration of antibiotics or probiotics on chickens in their first week of life, on selected parameters of humoral and cellular immunity, and on the bursa of Fabricius and spleen indices. The experiment was carried out on 90 one-day-old male broilers. The control group received no additive in the drinking water; the group GP received a probiotic providing Enterococcus faecium and Bacillus amyloliquefaciens; and the group GA received 10% enrofloxacin in the drinking water on the first five days of life. Administration of the antibiotic enrofloxacin or a probiotic containing E. faecium and B. amyloliquefaciens strains to chickens in their first week of life exerts pronounced immunomodulatory effects on humoral and cellular defense mechanisms in these birds. The changes in the subpopulations of B and T cells immediately following early administration of enrofloxacin or the probiotic were not observed at the age of 35 days. Early administration of enrofloxacin can pose a risk of suppression of humoral immunity, as indicated by the significant decrease in the total IgY concentration in the plasma of the chickens.

Effect of a Mineral-Microbial Deodorizing Preparation on the Functions of Internal Organs and the Immune System in Commercial Poultry

Animal production is identified as one of the main sources of high concentrations of odours, which are related to air pollution, health problems of living organisms and indirect negative impact on production results. One common method for reducing emissions of ammonia is using preparations containing probiotics and hygroscopic or disinfecting compounds. This study was undertaken in order to determine the impact of innovative mineral-microbial deodorizing preparation, which reduces odorous gases, applying to the litter once a week in poultry houses on the physiological status of breeder chickens, broiler chickens and turkeys. Samples were collected after slaughter and analyzed using ELISA tests, flow cytometry and biochemical methods. Biochemical markers of the liver and kidney profile (ALT, AST, LDH, ALP, CK, TP, CALC, PHOS) and the titers of specific antibodies against AEV, aMPV, AAvV-1, IBDV, HEV, BA were analyzed in serum samples. The percentage contribution of T and B lymphocyte subpopulations was determined in the samples of tracheal mucosa, blood, and spleen. No significant differences were found between the control and experimental group with regard to all the analyzed parameters, with some exceptions for biochemistry. The results of our study indicated that mineral-microbial deodorizing preparation did not affect the physiological status of birds.

The immune status, oxidative and epigenetic changes in tissues of turkeys fed diets with different ratios of arginine and lysine

In the present experiment, it was assumed that the appropriate dietary ratio of arginine (Arg) to lysine (Lys) can improve the immune status and growth performance of turkeys. The aim of this study was to evaluate the effects of two inclusion rates of Arg relative to Lys in turkey diets with Lys content consistent with National Research Council (NRC) recommendations or 10% higher on the immune status of birds and indicators of protein and DNA damage due to oxidation, nitration or epigenetic changes. Another goal was to determine which dietary Arg:Lys ratio stimulates the immune response of turkeys vaccinated against Ornithobacterium rhinotracheale. The experiment was performed on 576 turkeys randomly assigned to four groups with two levels of Lys (low = NRC recommendation or high = NRC + 10%) and two levels of Arg (95% or 105% Arg relative to the content of dietary Lys). It was found that the Lys content of turkey diets should be 10% higher than that recommended by the NRC and combined with the higher Arg level (105% of Lys). Although the above Arg:Lys ratio did not improve the growth performance of birds, it stimulated their immune system and reduced protein nitration as well as protein and DNA oxidation.

Phytoncides in The Prevention and Therapy of Blackhead Disease and Their Effect on The Turkey Immune System

Introduction

Turkey histomonosis poses a serious threat to poultry production due to the ban on the use of effective drugs. The aim of the study was to evaluate the influence of a phytoncidal feed supplement on the course of histomonosis. The preparation was also analysed for immunomodulatory properties.

Material and Methods

Clinical observations and production monitoring were conducted in a flock of turkeys with histomonosis from their 11^th to 56^th weeks of life which were treated with the adiCox^SOLPF soluble supplement in a dose of 2.5 mL/L water. Later the preparation was used in a preventive dose (1 mL/L). The influence on the immune system was evaluated in broiler turkeys having been given adiCox^SOLPF for 3 days in doses of 1 or 3 mL/L. The T and B lymphocyte percentages in turkey blood and spleen tissue were analysed with flow cytometry. ELISA was implemented to evaluate antibody titres after Ornithobacterium rhinotracheale vaccination, and biochemical analyses were performed to evaluate the supplement's safety.

Results

AdiCox^SOLPF was found effective in therapy and prevention of histomonosis. Additionally, adiCox^SOLPF stimulated both humoral and cell-mediated immune mechanisms, without impairing the functions of internal organs. The treated turkeys also yielded better production results (eggs/hen, fertility, and hatchability).

Conclusion

AdiCox^SOLPF possesses immunomodulatory properties and it can be used successfully in the prevention and therapy of histomonosis in turkeys.

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.

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.

The effect of different dietary levels of DL-methionine and DL-hydroxy analogue on the antioxidant status of young turkeys infected with the haemorrhagic enteritis virus

BACKGROUND

The results of experiments involving broiler chickens and turkeys indicate that increased dietary methionine (Met) levels may improve the antioxidant protection of tissues in fast-growing birds. This is an important consideration since viral infections induce oxidative stress. The aim of this study was to verify the hypothesis that turkey diets with increased Met content can suppress oxidation processes induced by infection caused by the haemorrhagic enteritis virus (HEV), and that the noted effect is determined by the chemical form of this amino acid: DL-methionine (DLM) or DL-hydroxy analogue of Met (MHA).

RESULTS

Dietary Met content above 40% higher than the level recommended by the NRC (1994) intensified lipid peroxidation in the small intestine, leading to an increase in malondialdehyde (MDA) and lipid peroxide (LOOH) levels, but it also stimulated antioxidant mechanisms in the blood and liver of turkeys infected with HEV. In comparison with DLM, MHA contributed to more severe symptoms of oxidative stress, such as elevated MDA levels in the intestines, and a decrease in glutathione peroxidase (GPx) activity and ferric-reducing ability of plasma (FRAP).

CONCLUSIONS

In HEV-infected turkeys, diets with increased Met content did not exert a clear antioxidant effect, which was noted in uninfected birds. The prooxidant activity of Met observed in the small intestinal wall was suppressed in the blood and liver of turkeys, most likely due to intensified synthesis of uric acid and glutathione. In comparison with MHA, DLM had a more beneficial influence on the analysed parameters of the redox status in the small intestine, blood and liver of turkeys.

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.

Biochemical and immunological responses of young turkeys to vaccination against Ornithobacterium rhinotraheale and different levels of dietary methionine

The objective of this study was to verify the hypothesis that increasing levels of dietary methionine can stimulate the mechanisms of cell-mediated and humoral immunity in young turkeys. The blood and organs involved in cell-mediated and humoral immune responses were analyzed in 8-week-old turkeys that had been vaccinated against Ornithobacterium rhinotraheale (ORT) infection (on days 17 and 48). The birds were fed diets with a low (LM), medium (MM) and high (HM) methionine content (0.45 and 0.40%, 0.60 and 0.51%, 0.71 and 0.57% in weeks 1 - 4 and 5 - 8, respectively). Dietary methionine supplementation led to a significant increase in body weights of turkeys at 56 days of age, from 3532 g in group LM to 3720 g in group MM and 3760 g in group HM (p=0.001). A significant increase in vaccine-induced antibody titers against ORT was noted in group HM relative to group LM (p=0.006). Increasing levels of methionine had no significant effect on total serum IgG nor IgM levels and most serum biochemical parameters, TP, ALB, GLOB, GLU, AST, ALP, P and Ca. In comparison with group LM, group HM turkeys were characterized by a lower percentage of IgM⁺ B cell subpopulation in the blood and bursa of Fabricius. The percentages of CD4⁺ and CD8⁺ T cell subpopulations in the bursa of Fabricius in group HM were significantly different from those found in groups LM and MM. The highest percentages of CD4⁺ T cells and CD8⁺ T cells in the spleen were observed in groups LM (p<0.001) and HM (p=0.04), respectively. The differences were statistically significant relative to the remaining groups. Turkeys of group LM were characterized by a lower CD4⁺ T cell percentage in the thymus (p<0.001) and a lower CD8⁺ T cell percentage in the cecal tonsils (CTs) (p<0.01). Vaccination against ORT resulted in a significant increase in the percentage of CD4⁺CD8⁺ T cell subpopulation and a decrease in the percentage of CD8⁺ T cell subset in the spleen.

The influence of phytoncides on the immune system of broiler chickens and turkeys

The aim of our study was to investigate the influence of adiSalmoSOL PF dietary supplement, given for 3 days in drinking water, on selected parameters of cell-mediated (Experiment I) and humoral (Experiment II) immunity in chicken and turkey broilers. In Experiment I, birds were randomly divided into two groups of 10 birds each. Group 1 comprised control turkeys or chickens, whereas group 2 birds were administered adiSalmo^SOLPF. In Experiment II, a total of 69 chickens were divided into three groups (1-3) of 23 birds each. At the age of 25 days, group 1 was given adiSalmo^SOLPF. Birds from groups 1-3 were vaccinated at 28 days of age. Group 2 was given adiSalmo^SOLPF after vaccination. In Experiment I, a significant increase in percentages of CD4 + T lymphocytes in the bursa of Fabricius, cecal tonsils and spleen, CD8 + T lymphocytes in the thymus and spleen, CD4 + CD8 + T lymphocytes in the bursa of Fabricius and ileal mucosa and IgM + B lymphocyte in the ileal mucosa were observed in group 2 chickens. In Experiment I, a significant increase in percentages of CD4 + T lymphocytes in the thymus and spleen, CD8+ T lymphocytes in the cecal tonsils and blood, and CD4 + CD8 + T lymphocytes in the thymus and ileal mucosa was recorded in group 2 turkeys. No differences in percentages of IgM + B lymphocytes were observed between turkey groups. In Experiment II, the highest post-vaccination titers of anti-IB antibodies were observed in group 2, but it was not statistically significant. The results of our study indicate that adiSalmo^SOLPF showed immunomodulatory activity in chickens and turkeys.

Immunological and biochemical indicators in turkeys fed diets with a different Methionine content

The objective of this study was to determine the effect of different levels of dietary methionine on selected immune parameters of young turkeys. A total of 357 one-day-old female Hybrid Converter turkeys were randomly divided into three groups with low, medium and high level of dietary me- thionine (LM, MM, HM) of seven replicates each. Methionine was added to the basal diet (LM) at 0.16% (MM) and 0.32% (HM). At 17 days of age, seven birds per group were vaccinated against Ornithobacterium rhinotraheale (ORT) infection, with ORNITIN (ABIC) vaccine. At 28 days of age, blood was sampled and the birds were euthanized. The serum concentrations and activity of selected biochemical parameters, total IgY and IgM, and vaccine-induced antibody titers (IgY) against ORT were determined. The percentages of CD4+, CD8+, CD4+/CD8+ T cell subpopulations and IgM+ B cell subpopulation were determined in blood and organs by flow cytometry. Different supplementary levels of methionine had no significant effect on vaccine-induced anti- body titers against ORT or total serum IgM and IgY levels, as well as on the percentages of periph- eral blood T and B cell subsets. Increasing dietary methionine rates decreased the percentage of CD4+ T cell subpopulation, however it has increased the percentage of IgM+ B cell subpopulation in the spleen. Vaccination against ORT resulted in a significant decrease in the percentage of CD4+ T cell subset and an increase in the percentage of CD8+ T cell subset in the spleen. It could be concluded that MM turkeys have developed the most desirable values of immune parameters.

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 14 weeks 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.