Immune dysfunction following infection with chicken anemia agent and infectious bursal disease virus. I. Kinetic alterations of avian lymphocyte subpopulations

Infectious bursal disease virus: predicting viral pathotype using machine learning models focused on early changes in total blood cell counts

Infectious bursal disease (IBD) is an avian viral disease caused in chickens by infectious bursal disease virus (IBDV). IBDV strains (Avibirnavirus genus, Birnaviridae family) exhibit different pathotypes, for which no molecular marker is available yet. The different pathotypes, ranging from sub-clinical to inducing immunosuppression and high mortality, are currently determined through a 10-day-long animal experiment designed to compare mortality and clinical score of the uncharacterized strain with references strains. Limits of this protocol lie within standardization and the extensive use of animal experimentation. The aim of this study was to establish a predictive model of viral pathotype based on a minimum number of early parameters measured during infection, allowing faster pathotyping of IBDV strains with improved ethics. We thus measured, at 2 and 4 days post-infection (dpi), the blood concentrations of various immune and coagulation related cells, the uricemia and the infectious viral load in the bursa of Fabricius of chicken infected under standardized conditions with a panel of viruses encompassing the different pathotypes of IBDV. Machine learning algorithms allowed establishing a predictive model of the pathotype based on early changes of the blood cell formula, whose accuracy reached 84.1%. Its accuracy to predict the attenuated and strictly immunosuppressive pathotypes was above 90%. The key parameters for this model were the blood concentrations of B cells, T cells, monocytes, granulocytes, thrombocytes and erythrocytes of infected chickens at 4 dpi. This predictive model could be a second option to traditional IBDV pathotyping that is faster, and more ethical.

Physiological parameter values for physiologically based pharmacokinetic models in food-producing animals. Part II: Chicken and turkey

Physiologically based pharmacokinetic (PBPK) models are growing in popularity due to human food safety concerns and for estimating drug residue distribution and estimating withdrawal intervals for veterinary products originating from livestock species. This paper focuses on the physiological and anatomical data, including cardiac output, organ weight, and blood flow values, needed for PBPK modeling applications for avian species commonly consumed in the poultry market. Experimental and field studies from 1940 to 2019 for broiler chickens (1-70 days old, 40 g - 3.2 kg), laying hens (4-15 months old, 1.1-2.0 kg), and turkeys (1 day-14 months old, 60 g -12.7 kg) were searched systematically using PubMed, Google Scholar, ProQuest, and ScienceDirect for data collection in 2019 and 2020. Relevant data were extracted from the literature with mean and standard deviation (SD) being calculated and compiled in tables of relative organ weights (% of body weight) and relative blood flows (% of cardiac output). Trends of organ or tissue weight growth during different life stages were calculated when sufficient data were available. These compiled data sets facilitate future PBPK model development and applications, especially in estimating chemical residue concentrations in edible tissues to calculate food safety withdrawal intervals for poultry.

Comparative study on dynamic and immunopathology of four intermediate-plus infectious bursal disease (IBD) vaccines in commercial broiler chickens

INTRODUCTION

The selection of the right IBD control strategy is primarily based on the choice of the appropriate vaccine strain. High maternal IBD-specific antibodies (Abs) compete with the efficacy IBD vaccine, which necessitates the application of intermediate-plus vaccine strain.

METHODS

A comparative experimental study was designed for evaluation of four different commercially available intermediate-plus IBD vaccines in commercial broilers before complete weaning of IBD-specific maternal Abs.

RESULTS

As determined by IBD- specific quantitative real-time polymerase chain reaction, three tested vaccine strains (228E, Winterfield H2512, and Winterfield 2512) were able to establish in the bursal tissues as early as six hours (hrs) post-vaccination (PV). Both the 228E and the Winterfield H2512 strains vaccinated groups had the highest viral load and replication rate in the bursal tissues at 24, 36, 48 and 72 hrs PV. Earlier seroconversion, 7-14 days PV, was observed in the case of Winterfield H2512, 228E, and Winterfield 2512 vaccinated birds compared to the Lukert vaccinated birds. The 228E strain was more virulent and induces the highest lesion score with severe degrees of lymphocyte depletion and necrosis which persisted up to 28 days PV.

CONCLUSION

Overall, the different intermediate-plus IBD strains possess variable early kinetics in the bursal tissues and eliciting antibody (Ab) responses differently withdifferent degrees of bursal lesions. The assessment of the intrabursal vaccine load together with humoral immunity and bursal damage lesion score are fundamental parameters in the evaluation of the intermediate-plus IBD vaccines.

The Stronger Downregulation of in vitro and in vivo Innate Antiviral Responses by a Very Virulent Strain of Infectious Bursal Disease Virus (IBDV), Compared to a Classical Strain, Is Mediated, in Part, by the VP4 Protein

IBDV is economically important to the poultry industry. Very virulent (vv) strains cause higher mortality rates than other strains for reasons that remain poorly understood. In order to provide more information on IBDV disease outcome, groups of chickens (n = 18) were inoculated with the vv strain, UK661, or the classical strain, F52/70. Birds infected with UK661 had a lower survival rate (50%) compared to F52/70 (80%). There was no difference in peak viral replication in the bursa of Fabricius (BF), but the expression of chicken IFNα, IFNβ, MX1, and IL-8 was significantly lower in the BF of birds infected with UK661 compared to F52/70 (p < 0.05) as quantified by RTqPCR, and this trend was also observed in DT40 cells infected with UK661 or F52/70 (p < 0.05). The induction of expression of type I IFN in DF-1 cells stimulated with polyI:C (measured by an IFN-β luciferase reporter assay) was significantly reduced in cells expressing ectopic VP4 from UK661 (p < 0.05), but was higher in cells expressing ectopic VP4 from F52/70. Cells infected with a chimeric recombinant IBDV carrying the UK661-VP4 gene in the background of PBG98, an attenuated vaccine strain that induces high levels of innate responses (PBG98-VP4UK661) also showed a reduced level of IFNα and IL-8 compared to cells infected with a chimeric virus carrying the F52/70-VP4 gene (PBG98-VP4F52/70) (p < 0.01), and birds infected with PBG98-VP4UK661 also had a reduced expression of IFNα in the BF compared to birds infected with PBG98-VP4F52/70 (p < 0.05). Taken together, these data demonstrate that UK661 induced the expression of lower levels of anti-viral type I IFN and proinflammatory genes than the classical strain in vitro and in vivo and this was, in part, due to strain-dependent differences in the VP4 protein.

Combination of TLR2 and TLR3 agonists derepress infectious bursal disease virus vaccine-induced immunosuppression in the chicken

Live intermediate plus infectious bursal disease virus (IBDV) vaccines (hot vaccines) are used for protection against the virulent IBDV strains in young chickens. We evaluated the potential of Toll-like receptor (TLR) agonists to alleviate hot vaccine-induced immunosuppression. The combination of Pam3CSK4 and poly I:C synergistically upregulated IFN-β, IFN-γ, IL-12, IL-4, and IL-13 transcripts and cross-inhibited IL-1β, IL-10, and iNOS transcripts in the chicken peripheral blood mononuclear cells (PBMCs) as analyzed by quantitative real-time PCR. Further, four-week old specific pathogen free White Leghorn chickens (n = 60) were randomly divided into six groups and either immunized with hot IBDV vaccine with or without Pam3CSK4 and/or poly I:C or not vaccinated to serve as controls. The results indicated that poly I:C alone and in combination with Pam3CSK4 alleviated vaccine-induced immunosuppression, as evidenced by greater weight gain, increased overall antibody responses to both sheep erythrocytes and live infectious bronchitis virus vaccine, upregulated IFN-γ transcripts and nitric oxide production by PBMCs (P < 0.05), and lower bursal lesion score in the experimental birds. In conclusion, poly I:C alone and its combination with Pam3CSK4 reduced the destruction of B cells as well as bursal damage with restoration of function of T cells and macrophages when used with a hot IBDV vaccine.

Molecular epidemiology of chicken anaemia virus in sick chickens in China from 2014 to 2015

Chicken anaemia virus (CAV), a member of the genus Gyrovirus, is the etiological agent of chicken infectious anaemia. CAV infects bone marrow-derived cells, resulting in severe anaemia and immunosuppression in young chickens and a compromised immune response in older birds. We investigated the molecular epidemiology of CAV in sick chickens in China from 2014 to 2015 and showed that the CAV-positive rate was 13.30%, in which mixed infection (55.56%) was the main type of infection. We isolated and identified 15 new CAV strains using different methods including indirect immunofluorescence assay and Western Blotting. We used overlapping polymerase chain reaction to map the whole genome of the strains. Phylogenetic analyses of the obtained sequences and related sequences available in GenBank generated four distinct groups (A-D). We built phylogenetic trees using predicted viral protein (VP) sequences. Unlike CAV VP2s and VP3s that were well conserved, the diversity of VP1s indicated that the new strains were virulent. Our epidemiological study provided new insights into the prevalence of CAV in clinical settings in recent years in China.

Simultaneous detection of eight immunosuppressive chicken viruses using a GeXP analyser-based multiplex PCR assay

BACKGROUND

Immunosuppressive viruses are frequently found as co-infections in the chicken industry, potentially causing serious economic losses. Because traditional molecular biology methods have limited detection ability, a rapid, high-throughput method for the differential diagnosis of these viruses is needed. The objective of this study is to develop a GenomeLab Gene Expression Profiler Analyser-based multiplex PCR method (GeXP-multiplex PCR) for simultaneous detection of eight immunosuppressive chicken viruses.

RESULTS

Using chimeric primers, eight such viruses, including Marek's disease virus (MDV), three subgroups of avian leucosis virus (ALV-A/B/J), reticuloendotheliosis virus (REV), infectious bursal disease virus (IBDV), chicken infectious anaemia virus (CIAV) and avian reovirus (ARV), were amplified and identified by their respective amplicon sizes. The specificity and sensitivity of the optimised GeXP-multiplex PCR assay were evaluated, and the data demonstrated that this technique could selectively amplify these eight viruses at a sensitivity of 100 copies/20 μl when all eight viruses were present. Among 300 examined clinical specimens, 190 were found to be positive for immunosuppressive viruses according to this novel assay.

CONCLUSION

The GeXP-multiplex PCR assay is a high-throughput, sensitive and specific method for the detection of eight immunosuppressive viruses and can be used for differential diagnosis and molecular epidemiological surveys.

Comparative histopathological and immunological study of two field strains of chicken anemia virus

Infection of poultry with chicken anemia virus (CAV) is implicated in several field problems in broiler flocks due to the immunosuppression generated and, consequently, the increased susceptibility to secondary infections. Recently, we have reported an increased occurrence of clinical cases caused by CAV strains distantly related to those commonly used for vaccination. In order to understand the behavior of two Argentinean CAV strains (CAV-10 and CAV-18) in two-week-old chickens, an immune and histopathological study was performed. Neither mortality nor clinical signs were observed in the infected or control groups. Thymus lobes from chickens infected with both CAV viruses were smaller compared to the negative control group. At 14 days post-infection (dpi), only chickens inoculated with CAV-10 show a severe depletion of lymphocytes in the thymus cortex and in follicles from the bursa of Fabricius. Also thymopoiesis disorders, such as reduction in the percentage of total DP (CD4 + CD8α+) thymocytes and alteration in the percentages of DP subpopulations, were more important in animals inoculated with the CAV-10 than the CAV-18 strain. In addition, only animals infected with CAV-10 show a decrease in CD8αβ splenocytes. Altogether our results show that, although both Argentinean CAV strains produce subclinical infections in chickens causing immunosuppression at 14 dpi, they might differ in their in vivo pathogenicity.

Infectious Bursal Disease: a complex host-pathogen interaction

Infectious Bursal Disease (IBD) is caused by a small, non-enveloped virus, highly resistant in the outside environment. Infectious Bursal Disease Virus (IBDV) targets the chicken's immune system in a very comprehensive and complex manner by destroying B lymphocytes, attracting T cells and activating macrophages. As an RNA virus, IBDV has a high mutation rate and may thus give rise to viruses with a modified antigenicity or increased virulence, as emphasized during the last decades. The molecular basis of pathogenicity and the exact cause of clinical disease and death are still poorly understood, as it is not clearly related to the severity of the lesions and the extent of the bursal damage. Recent works however, pointed out the role of an exacerbated innate immune response during the early stage of the infection with upregulated production of promediators that will induce a cytokine storm. In the case of IBDV, immunosuppression is both a direct consequence of the infection of specific target immune cells and an indirect consequence of the interactions occurring in the immune network of the host. Recovery from disease or subclinical infection will be followed by immunosuppression with more serious consequences if the strain is very virulent and infection occurs early in life. Although the immunosuppression caused by IBDV is principally directed towards B-lymphocytes, an effect on cell-mediated immunity (CMI) has also been demonstrated therefore increasing the impact of IBDV on the immunocompetence of the chicken. In addition to its zootechnical impact and its role in the development of secondary infections, it may affect the immune response of the chicken to subsequent vaccinations, essential in all types of intensive farming. Recent progress in the field of avian immunology has allowed a better knowledge of the immunological mechanisms involved in the disease but also should give improved tools for the measurement of immunosuppression in the field situation. Although satisfactory protection may be provided by the induction of high neutralizing antibody titres, interference from parental antibodies with vaccination has become the most important obstacle in the establishment of control programs. In this context, recombinant HVT and immune complex vaccines show promising results.

Dual infections with low virulent chicken infectious anaemia virus (lvCIAV) and intermediate infectious bursal disease virus (iIBDV) in young chicks increase lvCIAV in thymus and bursa while decreasing lymphocyte disorders induced by iIBDV

The use of attenuated vaccines or the occurrence of low virulent T-lymphotropic or B-lymphotropic viruses in flocks may alter the immune responses of young chicks in spite of the absence of clinical signs. Infections with a low virulent T-lymphotropic chicken infectious anaemia virus (lvCIAV) followed by infection with an intermediate B-lymphotropic infectious bursal disease virus (iIBDV) were conducted in specific pathogen free chicks. Thirty-six 1-day-old chicks were infected with the lvCIAV strain (CAV-VAC®) and a similar number of chicks were inoculated with phosphate-buffered saline. At 14 days after lvCIAV infection, one group of 18 lvCIAV-infected chicks and one group of 18 uninfected chicks were infected with an iIBDV strain. At 4, 7 and 14 days post infection with iIBDV, six chicks from each group were euthanized and lymphoid organs were collected. Detection of lvCIAV and iIBDV genomes was conducted by polymerase chain reaction and reverse transcriptase-polymerase chain reaction, respectively. Double-labelled lymphoid subsets from the thymus, spleen and bursa were studied by cytofluorometric analysis. The results reveal that previous infection with lvCIAV increases the occurrence of the lvCIAV and iIBDV genome in thymus and/or bursa without the occurrence of clinical signs in dually lvCIAV/iIBDV-infected chicks. However, the decreases of B cells in spleen and bursa and increases of T-cell subsets in bursa observed in chicks infected with iIBDV did not occur in chicks previously infected with lvCIAV. Taken together, these results suggest that previous infection of young chicks with lvCIAV decreases lymphoid disorders induced by iIBDV while subsequent iIBDV infection increases the lvCIAV genome in lymphoid organs.

Circoviruses: immunosuppressive threats to avian species: a review

Circoviruses are small, non-enveloped, icosahedral viruses that are unique among animal viruses in having circular, single-stranded DNA genomes. Their genomes are also the smallest possessed by animal viruses. The circovirus family currently comprises three members, chicken anaemia virus, porcine circovirus, and psittacine beak and feather disease virus, with pigeon circovirus being classified as a tentative member. Infections with each of the four circoviruses are associated with potentially fatal diseases in which virus-induced damage to lymphoid tissue and immunosuppression are common features. Experience with other animal virus families suggests that additional animal species will be infected by, as yet undiscovered, circoviruses and that these may display similar tissue tropism and disease-causing potential. Recent reports describing the association of circovirus-like viruses with immunodeficiency-related diseases of geese and southern black-backed gulls suggest that circovirus infections of avian species may be more common than previously recognized, and prompt the question of whether novel circoviruses infect poultry to cause clinical and/or subclinical diseases that may be economically important. This review has three purposes. First, it is designed to summarize the currently available information about the classified circoviruses and viruses that are regarded as circovirus-like. Second, it aims to alert the readership to the possibility that other avian species, including commercial poultry, may be infected with novel circoviruses. Finally, possible methods for discovering novel circoviruses and for controlling infections by such viruses are suggested.

Effects of chicken anaemia virus and infectious bursal disease virus-induced immunodeficiency on infectious bronchitis virus replication and genotypic drift

We followed changes in a portion of the S1 gene sequence of the dominant populations of an infectious bronchitis virus (IBV) Arkansas (Ark) vaccine strain during serial passage in chickens infected with the immunosuppressive chicken anaemia virus (CAV) and/or infectious bursal disease virus (IBDV) as well as in immunocompetent chickens. The IBV-Ark vaccine was applied ocularly and tears were collected from infected chickens for subsequent ocular inoculation in later passages. The experiment was performed twice. In both experiments the dominant S1 genotype of the vaccine strain was rapidly and negatively selected in all chicken groups (CAV, IBDV, CAV+IBDV and immunocompetent). Based on the S1 genotype, the same IBV subpopulations previously reported in immunocompetent chickens and named component (C) 1 to C5 emerged both in immunocompetent and immunodeficient chickens. During the first passage different subpopulations emerged, followed by the establishment of one or two predominant populations after further passages. Only when the subpopulation designated C2 became established in either CAV-infected or IBDV-infected chickens was IBV maintained for more than four passages. These results indicate that selection does not cease in immunodeficient chickens and that phenotype C2 may show a distinct adaptation to this environment. Subpopulations C1 or C4 initially became established in immunocompetent birds but became extinct after only a few succeeding passages. A similar result was observed in chickens co-infected with CAV+IBDV. These results suggest that the generation of genetic diversity in IBV is constrained. This finding constitutes further evidence for phenotypic drift occurring mainly as a result of selection.

Infectious bronchitis virus in the chicken Harderian gland and lachrymal fluid: viral load, infectivity, immune cell responses, and effects of viral immunodeficiency

We compared detection of infectious bronchitis virus (IBV) by quantitative RT-PCR (qRT-PCR) in tears and trachea of IBV-infected chickens and found that quantitative detection of IBV RNA in tears is more sensitive than in tracheal homogenates. Furthermore, we demonstrated that IBV contained in chicken lachrymal fluid is infectious and that tears of IBV-infected chickens can be used to infect naive chickens. We compared the immune responses to IBV in the Harderian gland and cecal tonsils of immunocompetent chickens and chickens infected with chicken anemia virus (CAV) and/or infectious bursal disease virus (IBDV). Flow cytometry analyses of lymphocytes in Harderian glands and cecal tonsils indicated that the relative abundance of IgM+ B cells in the Harderian glands and cecal tonsils following exposure to IBV in combination with immunosuppressive viruses was reduced compared to chickens infected with IBV alone. CAV, but not IBDV, reduced the CD4+/CD8+ T cell ratios compared to chickens infected with IBV alone. Enzyme-linked immuno-spot forming assays on cells in the Harderian glands and cecal tonsils of IBV-infected chickens indicated that maximum IBV-specific IgA-secreting cell responses were reduced in chickens infected with CAV. IBDV co-infected chickens displayed a delayed IgA response to IBV. Thus immunosuppressive viruses reduced B cells and T helper cells in the Harderian glands and cecal tonsils in response to IBV, and slowed the kinetics and/or reduced the magnitude of the mucosal immune response against IBV. We have shown for the first time that CAV affects pathogen-specific B cell responses in a mucosal effector site.

Chicken anemia virus

Chicken anemia virus (CAV), the only member of the genus Gyrovirus of the Circoviridae, is a ubiquitous pathogen of chickens and has a worldwide distribution. CAV shares some similarities with Torque teno virus (TTV) and Torque teno mini virus (TTMV) such as coding for a protein inducing apoptosis and a protein with a dual-specificity phosphatase. In contrast to TTV, the genome of CAV is highly conserved. Another important difference is that CAV can be isolated in cell culture. CAV produces a single polycistronic messenger RNA (mRNA), which is translated into three proteins. The promoter-enhancer region has four direct repeats resembling estrogen response elements. Transcription is enhanced by estrogen and repressed by at least two other transcription factors, one of which is COUP-TF1. A remarkable feature of CAV is that the virus can remain latent in gonadal tissues in the presence or absence of virus-neutralizing antibodies. In contrast to TTV, CAV can cause clinical disease and subclinical immunosuppression especially affecting CD8+ T lymphocytes. Clinical disease is associated with infection in newly hatched chicks lacking maternal antibodies or older chickens with a compromised humoral immune response.

Pivotal role of ChIFNgamma in the pathogenesis and immunosuppression of infectious bursal disease

This study investigates the pivotal role of chicken interferon-gamma (ChIFNgamma) in the pathogenesis and immunosuppression of infectious bursal disease virus (IBDV) infection and is divided into in vivo, ex vivo and in vitro experiments. Two-week-old specific pathogen free chickens were inoculated with the 849VB very virulent strain of IBDV. The levels of systemic ChIFNgamma and chicken interleukin-6 in the serum were followed for 2 weeks during in vivo experiments. Then, splenocytes and bursal cells from infected chickens were analysed for their immunocompetence after mitogenic activation in ex vivo experiments. Finally, in vitro experiments were conducted to assess the direct immunosuppressive effect of ChIFNgamma on splenocytes and peripheral blood lymphocytes from non-inoculated specific pathogen free chickens. Our results reveal that the acute phase of infectious bursal disease coincides, on one hand, with high levels of systemic ChIFNgamma and chicken interleukin-6 and, on the other hand, with a strong inhibition of proliferation and activation of mitogen-stimulated splenocytes from infected chickens, as measured by ChIFNgamma production. Two weeks after viral inoculation, T lymphocytes infiltrating the bursa of Fabricius had recovered their activation capability. Finally, an in vitro study showed that the proliferation of naïve splenocytes and peripheral blood lymphocytes was directly and specifically inhibited by ChIFNgamma. In conclusion, a ChIFNgamma dysregulation occurs in chickens infected with IBDV and the overproduction of ChIFNgamma by T lymphocytes plays a key role in the pathogenesis and immunosuppression induced by this virus.

Epidemiological and experimental evidence for immunodeficiency affecting avian infectious bronchitis

We evaluated the effects of viral immunodeficiency on the outcome of infectious bronchitis virus (IBV) infection in chickens as a hypothetical cause for failure of adequate protection in vaccinated chickens. Initially, we investigated IBV isolations from cases of respiratory disease in association with the presence of thymic and/or bursal atrophy in 322 submissions during 1997 to 2002. Arkansas (Ark)-type IBV was most frequently isolated in spite of extensive ArkDPI vaccination in the broiler industry. The number of IBV isolations was consistently higher in broilers aged 27 to 43 days, coinciding with lymphocytic depletion of the bursa and/or thymus, providing circumstantial evidence that immunodeficiency and IBV incidence may be linked. S1 gene sequence analyses, antigenic characterizations, and challenge of susceptible chickens demonstrated that the field IBV isolates tested were closely related to vaccine strains and had low pathogenicity for chickens. We experimentally evaluated the effects of immunodeficiency caused by co-infection with chicken anaemia virus and infectious bursal disease virus on the outcome of IBV infection. Clinical signs and histological lesions were more persistent in immunodeficient chickens. Local specific IgA production was delayed and lower levels were achieved in immunodeficient chickens. At the same time, IBV RNA concentrations in tracheas and lachrymal fluids were higher and more persistent in immunodeficient chickens. Collectively, these results indicate that viral immunodeficiency most probably plays a relevant role in the epidemiology and outcome of IBV infection.

Economically important non-oncogenic immunosuppressive viral diseases of chicken--current status

Immunosuppressive viral diseases threaten the poultry industry by causing heavy mortality and economic loss of production, often as a result of the chickens' increased susceptibility to secondary infections and sub-optimal response to vaccinations. This paper aimed to present an up-to-date review of three specific economically important non-oncogenic immunosuppressive viral diseases of chickens, viz. chicken infectious anaemia (CIA), infectious bursal disease (IBD) and hydropericardium syndrome (HPS), with emphasis on their immunosuppressive effects. CIA and IBD causes immunosuppression in chickens and the socio-economic significance of these diseases is considerable worldwide. CIA occurs following transovarian transmission of chicken anaemia virus and has potential for inducing immunosuppression alone or in combination with other infectious agents, and is characterized by generalized lymphoid atrophy, increased mortality and severe anemia. The virus replicates in erythroid and lymphoid progenitor cells, causing inapparent, sub-clinical infections that lead to depletion of these cells with consequent immunosuppressive effects. The IBD virus replicates extensively in IgM(+) cells of the bursa and chickens may die during the acute phase of the disease, although IBD virus-induced mortality is highly variable and depends, among other factors, upon the virulence of the virus strain. The sub-clinical form is more common than clinical IBD because of regular vaccination on breeding farms. Infection at an early age significantly compromises the humoral and local immune responses of chickens because of the direct effect of B cells or their precursors. HPS is a recently emerged immunosuppressive disease of 3-6-weeked broilers, characterized by sudden onset, high mortality, typical hydropericardium and enlarged mottled and friable livers, with intranuclear inclusion bodies in the hepatocytes. The agent, fowl adenovirus-4, causes immunosuppression by damaging lymphoid tissues; the presence of IBD and CIA viruses may predispose for HPS or HPS may predispose for other viral infections. Synergism with CIA or other virus infections or prior immunosuppression is necessary to produce IBH-HPS in chickens and the susceptibility of chickens infected with fowl adenovirus varies throughout the course of CIA infection. The mechanism of immunosuppression has been studied in detail for certain chicken viruses at molecular levels, which will provides new opportunities to control these diseases by vaccination.

Characterization and Phylogenetic Analysis of Brazilian Chicken Anaemia Virus

Chicken anaemia virus (CAV) was detected by a Nested-PCR assay in field samples from different regions of Brazil. The 539 bp amplified fragments of vp1 gene from 44 field samples were sequenced and 10 new nucleotide sequences of CAV were observed. These sequences were phylogenetically analysed by Mega2 using neighbour joining distance methods with 1000 bootstrap replications. Phylogenetic analysis did not show correlation between CAV pathology pattern and genetic groups. The 10 nucleotide sequences of the Brazilian samples were also analysed together with 30 sequences of CAV strains previously described from other countries. The genetic variability observed was not related to the geographical distribution. Amino acid substitutions were detected at 9 positions of the Brazilian sequences and two of them had not been observed before, (65)R replacing the Q residue and (98)F replacing Y residue.

Oral Infection with Chicken Anemia Virus in 4-Wk Broiler Breeders: Lack of Effect of Major HistocompatibilityBComplex Genotype

The pathologic consequences of chicken anemia virus (CAV) oral inoculation in 4-wk-old broiler breeders of different major histocompatibility B complex (MHC) genotypes were evaluated. MHC B complex was determined by hemagglutination and sequence-based typing. Clinical signs, serology, gross lesions, histopathologic analysis, and CAV genome quantification were used to evaluate disease progression. Clinical disease was not apparent in the inoculated broilers throughout the experimental period. At 14 days postinoculation, antibodies against CAV were detected in 26.4% (29/110) of the inoculated birds. The distribution of percent positive was 34.6% (9/26) and 32.3% (10/31) of the chickens with B A9/A9 and B A9/A4 MHC genotypes, respectively, and seroconversion in six other genotypes was 19% (10/53). These differences among MHC genotypes for specific seroconversion rate were not statistically significant. CAV genomes were detected in the thymus of 87.7% (93/110) of the inoculated birds with no statistically significant differences between MHC genotypes. Mild thymic lymphocytolysis, lymphedema, and medullary hemorrhage were observed in the inoculated chickens. Histomorphometric analysis showed that cortical lymphocyte-to-parenchyma ratios did not differ between inoculated and uninoculated groups or among MHC genotypes. Similar findings have been reported previously in white-leghorn chickens of similar age, suggesting that broilers show a similar resistance to the effects of CAV infection at this age. The absence of significant clinical and pathological changes in the orally inoculated broilers at this age contrasts with CAV-associated thymus damage seen frequently in condemned commercial broilers at harvest.

Isolation and Preliminary Characterization of Chicken Anemia Virus from Chickens in Nigeria

Chicken anemia virus (CAV) was isolated for the first time from the Nigerian chicken population. The virus was recovered from necropsied birds from broiler and pullet flocks that suffered disease outbreaks tentatively diagnosed as infectious bursal disease. A sensitive polymerase chain reaction (PCR) assay detected CAV DNA in tissues of necropsied birds. Restriction endonuclease analysis performed with the 733-bp PCR product and the Cfo I enzyme indicated at least two different CAVs were circulating among the Nigerian chicken population. Four isolates were obtained from pooled liver and thymus tissues using the MDCC-MSB1 cell line. These isolates were found to be antigenically closely related to the Cuxhaven-1 (Cux-1) reference strain of CAV when reacted with four monoclonal antibodies prepared against the Cux-1 virus. One of the isolates (isolate A) induced thymus atrophy, bone marrow aplasia, and low hematocrit values when inoculated into 1-day-old specific-pathogen-free chickens. These findings not only demonstrate that CAV is present in Nigeria, but they also likely represent the first cell culture isolation of the virus in Africa.

Molecular epidemiology of chicken anemia virus in Nigeria

Between February 2002 and May 2004, chicken anemia virus (CAV) was detected by PCR in organ samples from 14 flocks of poultry farms in Lagos, Ogun and Oyo States in Southwestern Nigeria. The farms reported low (<5%) to high mortalities (up to 100%) with various lesions at necropsy. The complete VP1 gene of 30 of these positive strains was sequenced. Strains that diverged by up to 4.4% on a nucleotide level differed only by up to 2.5% at the amino acid level (7 aa) as a result of clustered silent mutations. No amino acid substitutions specific for Nigerian strains were observed. Some birds had a CAV mixed infection. Genetic clustering of the VP1 gene did not correlate with differences in flock mortality but the co-infection of CAV with IBDV may be particularly lethal. This first molecular epidemiological study of CAV in Africa shows that the Nigerian strains cluster with viruses from very diverse geographic origins and were almost as diverse (4.4%) as all other strains combined (5.8%).

Chicken Infectious Anemia Virus: An Example of the Ultimate Host–Parasite Relationship

Chicken infectious anemia virus (CIAV) is a resistant and ubiquitous virus of chickens causing disease in young chickens and immunosuppression in all birds. This paper reviews the current knowledge of CIAV with a focus on new findings indicating that immunosuppressive effects have not been fully appreciated, especially as they relate to the development of antigen-specific cytotoxic T cells. A more complete understanding of the immunosuppressive effects of CIAV emphasizes the need for better vaccines, especially for the broiler industry. In addition, a new model is proposed for the control of viral replication in the reproductive tract of specific-pathogen-free chickens, which may be latently infected. This model suggests that virus transcription is controlled by viral enhancer and repressor elements, which are regulated by different hormones. As a consequence, CIAV has a well-adapted relationship with its host, avoiding immune detection, ensuring passage of virus to the next generation, and eliciting limited pathology to the host.

Comparative analysis of Marek’s disease virus (MDV) glycoprotein-, lytic antigen pp38- and transformation antigen Meq-encoding genes: association of meq mutations with MDVs of high virulence

Marek's disease (MD) is a highly contagious lymphoproliferative and demyelinating disorder of chickens. MD is caused by Marek's disease virus (MDV), a cell-associated, acute-transforming alphaherpesvirus. For three decades, losses to the poultry industry due to MD have been greatly limited through the use of live vaccines. MDV vaccine strains are comprised of antigenically related, apathogenic MDVs originally isolated from chickens (MDV-2), turkeys (herpesvirus of turkeys, HVT) or attenuated-oncogenic strains of MDV-1 (CVI-988). Since the inception of high-density poultry production and MD vaccination, there have been two discernible increases in the virulence of MDV field strains. Our objectives were to determine if common mutations in the major glycoprotein genes, a major lytic antigen phosphoprotein 38 (pp38) or a major latency/transformation antigen Meq (Marek's EcoRI-Q-encoded protein) were associated with enhanced MDV virulence. To address this, we cloned and sequenced the major surface glycoprotein genes (gB, gC, gD, gE, gH, gI, and gL) of five MDV strains that were representative of the virulent (v), very virulent (vv) and very virulent plus (vv+) pathotypes of MDV. We found no consistent mutations in these genes that correlated strictly with virulence level. The glycoprotein genes most similar among MDV-1, MDV-2 and HVT (gB and gC, approximately 81 and 75%, respectively) were among the most conserved across pathotype. We found mutations mapping to the putative signal cleavage site in the gL genes in four out of eleven vv+MDVs, but this mutation was also identified in one vvMDV (643P) indicating that it did not correlate with enhanced virulence. In further analysis of an additional 12 MDV strains, we found no gross polymorphism in any of the glycoprotein genes. Likewise, by PCR and RFLP analysis, we found no polymorphism at the locus encoding the pp38 gene, an early lytic-phase gene associated with MDV replication. In contrast, we found distinct mutations in the latency and transformation-associated Marek's EcoRI-Q-encoded protein, Meq. In examination of the DNA and deduced amino acid sequence of meq genes from 26 MDV strains (9 m/vMDV, 5 vvMDV and 12 vv+MDVs), we found distinct polymorphism and point mutations that appeared to correlate with virulence. Although a complex trait like MDV virulence is likely to be multigenic, these data describe the first sets of mutations that appear to correlate with MDV virulence. Our conclusion is that since Meq is expressed primarily in the latent/transforming phase of MDV infection, and is not encoded by MDV-2 or HVT vaccine viruses, the evolution of MDV virulence may be due to selection on MDV-host cell interactions during latency and may not be mediated by the immune selection against virus lytic antigens such as the surface glycoproteins.

Effect of intravenous endotoxin on blood cell profiles of broilers housed in cages and floor litter environments

Commercial broilers are constantly exposed to airborne microorganisms and endotoxin (lipopolysaccharide, LPS). It has been shown that microbial contamination of the air was higher in broiler houses using floor litter than in broiler houses using netting-type floors. The current study evaluated the effect of housing conditions on blood leukocyte profiles and tested the hypothesis that, when compared to broilers reared in clean stainless steel cages (Cage group), broilers raised on floor litter (Floor group) should experience a higher environmental challenge and have a desensitized immune system that may exhibit better tolerance/resistance to subsequent intravenous LPS challenge. Hematological parameters were evaluated prior to and following i.v. administration of 1 mg/kg BW Salmonella typhimurium LPS (dissolved at 1 mg/0.25 mL in PBS) or i.v. injection of 0.25 mL/kg BW PBS alone. The results showed that prior to LPS/PBS injection, broilers in the cage group had higher heterophil and monocyte concentrations, a higher B cell percentage within the lymphocyte population, and a higher heterophil to lymphocyte (H:L) ratio in the blood. The i.v. LPS injection resulted in 25% mortality in the cage group and 42% mortality in the floor group within 8 h post-injection. LPS reduced the concentrations of total white blood cells (WBC) and all differential WBC except eosinophils and increased thrombocyte concentrations within 1 h post-injection in both groups. All of these values returned to their respective pre-injection levels within 48 h post-injection in the surviving birds. The two groups exhibited similar overall hematological changes after LPS injection except that the cage group showed a higher H:L ratio at 8 h post-injection and a lower B-cell percentage within the lymphocyte population at 48 h post-injection when compared with the floor group. We concluded that the immune systems of broilers reared on floor litter were desensitized and exhibited less pronounced leukocyte responses to i.v. LPS when compared with those of broilers reared in clean stainless steel cages. However, such desensitization of the immune system did not help broilers survive subsequent i.v. LPS challenge.

Characterization of a spontaneously transformed chicken mononuclear cell line

We describe the characterization of a spontaneously transformed chicken monocytic cell line that developed as a single colony of cells in a heterophil culture that was inadvertently left in the incubator over a period of 25 days. These cells, hitherto named HTC, grow efficiently at both 37 or 41 degrees C in culture medium containing either 5% FBS or 2% chicken serum. The HTC cells are acid phosphatase positive, show expressions of both class I and class II major histocompatibility complex (MHC), CD44, K1, and K55 cell surface antigens, and engulf latex beads, produce nitrite and interleukin-6 on stimulation with bacterial lipopolysaccharide (LPS). Treatment with phorbol myristate acetate (PMA) induces respiratory burst in HTC cells and the secretion of matrix metalloproteinase (MMP) into culture medium. Using gene-specific primers and reverse transcriptase-polymerase chain reaction (RT-PCR), the presence of mRNA trancripts for interferon-gamma (IFN-gamma), interleukin-1 (IL-1), interleukin-6 (IL-6), nitric oxide synthase (NOS), matrix metalloproteinase-2 (MMP-2), and transforming growth factor-beta (TGF-beta) were detected. Lipopolysaccharide (LPS) treatment of HTC cells modulated IL-1, IL-6, IFN-gamma, NOS mRNA levels as detected by RT-PCR analyses. Using different avian tumor virus gene-specific primers and PCR, the HTC cells were positive for the presence of avian leukosis virus (ALV) and Marek's disease virus (MDV) but negative for reticuloendothelial virus (REV), chicken infectious anemia virus (CIAV), and herpes virus of turkeys (HVT). The production of ALV antigens by HTC cells was further confirmed using p27 gag protein ELISA. Collectively, these results show that the HTC cells belong to myeloid/macrophage lineage and were likely transformed by ALV and MDV but retain many interesting and useful biological activities.

Immunopathologic Investigations with an Attenuated Chicken Anemia Virus in Day-Old Chickens

The immunopathologic effects induced by two attenuated chicken anemia virus (CAV) isolates, known as cloned isolate 34 (CI 34) and cloned revertant isolate 18 (CRI 18), that were derived from highly passaged pools of Cux-1 CAV isolate, were compared with those induced by a pathogenic, molecularly cloned, low-passage Cux-1 isolate (CI Cux). This comparison involved the intramuscular inoculation of 1-day-old specific-pathogen-free chicks with each of the viruses and investigation of birds at selected days postinoculation for gross pathology and depletions in the thymic T-cell populations as determined by flow cytometry. Whereas infection with the pathogenic CI Cux produced severe anemia and pronounced bone marrow and thymus lesions, infections with the attenuated CRI 18 and CI 34 isolates produced no anemia, no or mild lesions, respectively, and moderate T-cell depletion. The results suggest that, with CAV, reduced pathogenicity for 1-day-old chicks correlates with reduced depletion of T-cell populations in the thymus and with reduced severity of lesions in the thymus and bone marrow.

Sequence analysis of the full-length cloned DNA of a chicken anaemia virus (CAV) strain from Bangladesh: evidence for genetic grouping of CAV strains based on the deduced VP1 amino acid sequences

Chicken anaemia virus (CAV) was detected in the bursa of Fabricius of a 4-week-old chicken obtained from an outbreak of acute infectious bursal disease in Bangladesh. Repeated attempts to grow this virus in MDCC-MSB1 cells were not successful. A full-length PCR amplicon of the genome of this strain, designated as BD-3 CAV, was cloned and sequenced. The complete nucleotide sequence and the deduced amino acid sequence were compared with those of 12 other CAV strains. The genetic analysis of the amino acid sequences of VP1 indicated the possible existence of genetic groups among CAV strains, as BD-3 CAV along with four other strains (CIA-1, L-028, Isolate 704 and TR-20) formed a distinct lineage. These strains have four signatory amino acids in VP1, such as 75I/T, 97L, 139Q and 144Q, out of which the latter two are located in a small hydrophilic peak.

Antigen-specific T cell proliferation following coccidia infection

Coccidia antigen-specific T lymphocyte proliferation induced by Eimeria acervulina was measured in chickens congenic at the major histocompatibility complex and in two unrelated lines. Sporozoites and merozoites induced high proliferation of lymphocytes following primary infection, with similar changes seen for splenic or peripheral blood lymphocytes. Highest antigen-specific proliferation after both primary and secondary infection was seen in Line 15I5, which contributed the background genome to the congenic lines. In general, merozoites elicited higher proliferation responses than sporozoites. Analyses of differences between uninfected and infected chickens showed that, at some points in the infection cycle, proliferation of lymphocytes was greater and at other times less for infected than uninfected chickens.

Immune dysfunction following infection with chicken anemia agent and infectious bursal disease virus. II. Alterations of in vitro lymphoproliferation and in vivo immune responses

To determine the functional impact of alterations in lymphocyte concentrations and ratios following infection with chicken anemia agent (CAA) alone or in combination with infectious bursal disease virus (IBDV) on the immune system of young chickens, in vitro lymphoproliferation assays and in vivo responses to vaccination with several common viral agents were assessed at various time intervals post-inoculation (PI). Concanavalin A (Con A), phytohemagglutinin (PHA) and pokeweed mitogen (PWM) stimulation of splenic lymphocytes (SPL) collected from control birds could not be detected until 10-14 days PI. Infection with CAA was characterized by significantly higher PWM stimulation of SPL at 17 days PI and significantly lower PWM stimulation of peripheral blood lymphocytes (PBL) at 14 days PI, compared with uninfected controls. Concanavalin A and PWM stimulation of SPL was significantly increased in birds inoculated with IBDV alone. Lymphocytes harvested from birds inoculated simultaneously with CAA and IBDV had significantly lower responses. Effects on humoral and cell-mediated immunity following CAA and/or IBDV were determined by evaluating vaccination responses to Newcastle disease virus (NDV), fowl pox virus (FPV) and infectious laryngotracheitis virus (ILTV) during the acute phase of CAA infection (2 weeks PI). Vaccination of birds 2 weeks following CAA infection at 1 day of age resulted in decreased protection against NDV (85.7%) and ILTV (7.1%) challenge compared with protection rates in control birds (100% and 53.3% respectively). Infectious bursal disease virus infection was associated with decreased protection against NDV (60%) only. Concomitant infection at 1 day of age resulted in a greater reduction in NDV challenge protection (33.3%), slightly decreased FPV protection (87.5%), increased numbers of persistent FPV vaccination lesions and increased protection against ILTV challenge (71.4%). Vaccination of birds 2 weeks following CAA infection at 2 weeks of age resulted in slightly decreased NDV humoral antibody, development of persistent FPV vaccination lesions (17%) and increased immunity to ILTV challenge compared with control birds (83.3% vs. 66.7%). Chickens inoculated with IBDV alone displayed a more severe depression in NDV antibody titers and only a slight decrease in ILTV protection. Vaccination following concomitant infection at 2 weeks of age resulted in a higher percentage of FPV persistent vaccination lesions (39%) and greatly enhanced immunity to ILTV challenge (100%).