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

Genetic Sequence and Pathogenicity of Infectious Bursal Disease Virus in Chickens in Egypt During 2017-2021

The continued circulation of infectious bursal disease virus (IBDV) in Egypt, despite the use of various vaccines, is a serious problem that requires continuous detection of IBDV. In the current study, real-time reverse transcriptase polymerase chain reaction testing of 100 diseased chicken flocks during 2017-2021 revealed the presence of very virulent IBDV (vvIBDV) in 67% of the flocks, non-vvIBDV in 11%, and a mixture of both vvIBDV and non-vvIBDV in 4%. Twenty-nine IBDV isolates were submitted for partial sequencing of the viral protein 2 hypervariable region (VP2-HVR), and 27 isolates were confirmed to be genogroup A3 (vvIBDV) with 96.3%-98.5% similarity to the global A3 (vvIBDV) and 88.9%-97% similarity to genogroup A1 vaccine strains. The remaining two isolates were non-vvIBDV and showed 91.1% and 100% identity with classical genogroup A1 strains, respectively. Furthermore, the sequence and phylogenetic analysis of VP1 (amino acids 33-254) of two selected isolates of A3, 5/2017 and 98/2021, clustered them as B2, vvIBDV-like, strains with high similarity (99.5%) to four Egyptian, 99% to Chinese and European, and 97.7% to Chinese and Polish vvIBDV isolates. Experimental infection of commercial broiler chickens with two vvIBDV-A3B2 isolates (5/2017 and 98/2021) showed no mortality despite typical tissue lesions, clear histopathological changes, and strong ELISA antibody response. Isolate 98/2021 was more pathogenic, as confirmed by histopathology, whereas isolate 5/2017 induced a stronger serological response. In conclusion, vvIBDV (A3B2) strains with two amino acid (aa) substitutions in VP1 as V141I and V234I as well as VP2 as Y220F and G254S are still circulating in Egypt.

Isolation, Molecular, and Histopathological Patterns of a Novel Variant of Infectious Bursal Disease Virus in Chicken Flocks in Egypt

After an extended period of detecting classical virulent, attenuated, and very virulent IBDV, a novel variant (nVarIBDV) was confirmed in Egypt in this study in 18, IBD vaccinated, chicken flocks aged 19-49 days. Partial sequence of viral protein 2 (VP2) [219 aa, 147-366, resembling 657 bp] of two obtained isolates (nos. 3 and 4) revealed nVarIBDV (genotype A2d) and OR682618 and OR682619 GenBank accession numbers were obtained. Phylogenetic analysis revealed that both nVarIBDV isolates were closely related to nVarIBDV strains (A2d) circulating in China, exhibiting 100% identity to SD-2020 and 99.5-98.1% similarity to ZD-2018-1, QZ, GX and SG19 strains, respectively. Similarity to USA variant strains, belonging to genotypes A2b (9109), A2c (GLS) and A2a (variant E), respectively, was 95.5-92.6%. Also, the VP2 hypervariable region in those two, A2d, isolates revealed greater similarities to Faragher 52/70 (Vaxxitek®) at 90.4% and to an Indian strain (Ventri-Plus®) and V217 (Xtreme®) at 89.7% and 86-88.9% in other vaccines. Histopathological examination of both the bursa of Fabricius and spleen collected from diseased chickens in flock no. 18 revealed severe atrophy. In conclusion, further studies are required to investigate the epidemiological situation of this novel genotype across the country, and to assess various vaccine protections against nVarIBDV. Additionally, vaccination of breeders with inactivated IBD vaccines including this nVarIBDV is essential to obtain specific maternal antibodies in their broilers.

Molecular characterization of chicken infectious anaemia virus (CIAV) in China during 2020-2021

Chicken infectious anaemia virus (CIAV) has been identified as the causative agent of chicken infectious anaemia (CIA), causing huge economic losses to the poultry industry globally. In this study, a total of 573 clinical samples were collected from 197 broiler farms in 17 provinces of China during 2020-2021. Among them, 375 samples (375/573, 65.4%) were positive for CIAV by real-time PCR. The positive rate of CIAV detection between different regions of China ranged from 46.67% (North China) to 81.25% (Central China). The nucleotide sequences of the VP1 gene were obtained for 91 CIAV strains, whole genome sequencing was successful for 72 out of 91 strains. Phylogenetic analysis based on the VP1 gene revealed that 91 CIAV strains currently circulating in China belong to three genotypes (II, IIIa and IIIb), and most of the CIAV strains belong to genotype IIIa. Phylogenetic analysis of the whole genome showed that 71 CIAV strains belong to genotype IIIa, and one strain belongs to genotype II. Sequence analysis showed several amino acid substitutions in both the VP1, VP2 and VP3 proteins. Our results enhance the understanding of the molecular characterization of CIAV infection in China.RESEARCH HIGHLIGHTS A molecular systematic survey of CIAV in China during 2020-2021.CIAV genotype IIIa is the predominant genotype in China.

Molecular characterization of chicken anemia virus in Guangxi Province, southern China, from 2018 to 2020

Background

Chicken anemia virus (CAV) causes chicken infectious anemia, which results in immunosuppression; the virus has spread widely in chicken flocks in China.

Objectives

The aim of this study was to understand recent CAV genetic evolution in chicken flocks in Guangxi Province, southern China.

Methods

In total, 350 liver samples were collected from eight commercial broiler chicken farms in Guangxi Province in southern China from 2018 to 2020. CAV was detected by conventional PCR, and twenty CAV complete genomes were amplified and used for the phylogenetic analysis and recombination analysis.

Results

The overall CAV-positive rate was 17.1%. The genetic analysis revealed that 84 CAVs were distributed in groups A, B, C (subgroups C1-C3) and D. In total, 30 of 47 Chinese CAV sequences from 2005-2020 belong to subgroup C3, including 15 CAVs from this study. There were some specific mutation sites among the intergenotypes in the VP1 protein. The amino acids at position 394Q in the VP1 protein of 20 CAV strains were consistent with the characteristics of a highly pathogenic strain. GX1904B was a putative recombinant.

Conclusions

Subgroup C3 was the dominant genotype in Guangxi Province from 2018–2020. The 20 CAV strains in this study might be virulent according to the amino acid residue analysis. These data help improve our understanding of the epidemiological trends of CAV in southern China.

Development of lymphocyte subpopulations in local breed chickens

BACKGROUND AND AIM

Local breeds of chicken are known to have relatively higher disease resistance to many endemic diseases and diseases that are highly virulent in commercial chickens. This study aimed to address the lymphocyte subpopulations in three constitutive immune system organs (thymus, bursa of Fabricius, and spleen) in 30, 8-week-old, male local breed chickens.

MATERIALS AND METHODS

The T (CD3+) and B lymphocytes (Bu-1+) were identified through one-color, direct immunofluorescent staining of the thymus, bursa, and spleen lymphocytes. Likewise, two-color, direct immunofluorescent staining was performed to identify the CD4- and/or CD8-defined T lymphocytes. The proportions of T and B lymphocytes and CD4- and/or CD8 defined chicken lymphocyte subsets in lymphoid suspensions prepared from the thymus, bursa, and spleen were determined by flow cytometry.

RESULTS

CD3+ cells, particularly those positive for CD4+CD8-, were dominant in the thymus, whereas cells expressing the Bu-1 marker were predominant in the bursa of Fabricius. The proportion of T and B cells was almost equal in the spleen, with more cells expressing the CD4-CD8+ marker in the red pulp.

CONCLUSION

These findings indicate that local breeds of chicken could serve as a reliable model for studying the immune system of commercial light chicken breeds, due to the similarity in the presence and the distribution of the immune cells.

Origin, spreading and genetic variability of chicken anaemia virus

Chicken anaemia virus (CAV) is a widespread pathogen that causes immunosuppression in chickens. The virus-induced immunosuppression often results in secondary infections and a sub-optimal response to vaccinations, leading to high mortality rates and significant economic losses in the poultry industry. The small circular ssDNA genome (2.3 kb) has three partially overlapping genes: vp1, vp2 and vp3. VP1 capsid protein is highly variable and contains the neutralizing epitopes. Here, we analysed CAV strains from Uruguay using the full-length vp1 gene and performed a global comparative analysis to provide new evidence about the origin, dispersion and genetic variability of the virus. The phylogenetic analysis classified CAV in three or four major clades. Two clades (II and III) grouped most of the strains circulating worldwide including the Uruguayan strains. The phylodynamic analyses indicated that CAV emerged in the early 1900s and diverged to originate clade II and III. This early period of viral emergence was characterised by local diversification promoted by the extremely high substitution rate inferred for the virus (3.8 × 10^-4 substitutions/site/year). Later, the virus underwent a global spreading by intra- and inter-continental migrations that correlates with a significant rise in the effective population size. In South America, CAV was introduced in three different migratory events and spread across the continent. Our findings suggest that the current CAV distribution is the consequence of its continuous expansion capability that homogenizes the populations and prevents the detection of clear temporal and geographic patterns of evolution in most strains.RESEARCH HIGHLIGHTS Current strains of chicken anaemia virus emerged in Asia in the early 1900s.Chicken anaemia virus has a high substitution rate.The phylogenetic analysis classified chicken anaemia virus in four major clades.Evolution in South America was characterized by long migration and local spreading.

Chicken infectious anaemia virus infections in chickens in northern Vietnam: epidemiological features and genetic characterization of the causative agent

Since the first report of chicken infectious anaemia virus (CIAV) in Vietnam in 2013, there have not been many studies focused on the detection of CIAV or the molecular characteristics of the virus. This study attempted to investigate the presence of CIAV in northern Vietnam by molecular-based methods. Regarding the spatial distribution of CIAV, the PCR-based results showed that CIAV was detected in 47 out of 64 farms (73.4%) and in all 10 investigated provinces. Of the 119 samples assayed by PCR, 74 (62.2%) tested positive for CIAV DNA. By arranging the samples into different categories, it was found that CIAV was detected at high rates (above 50%) based on all 4 evaluated criteria as follows: production type of chicken, housing system, flock size and age group. Different housing systems were significantly associated with the detection rates of CIAV (P = 0.003). By genetic analyses, all of the Vietnamese CIAVs were found to (i) lack substitutions related to attenuation substitutions, (ii) group separately from vaccine-like CIAVs and (iii) belong to genogroups G2 and G3 of CIAV. Because of the wide distribution of CIAV and because the virus was confirmed not to be vaccine-like viruses, it is suggested that further studies be conducted on the clinical form of chicken infectious anaemia, as well as the immunosuppressive effect of CIAV on chickens in Vietnam.RESEARCH HIGHLIGHTS Wide distribution of chicken infectious anaemia virus (CIAV) in northern Vietnam.Vietnamese CIAVs belong to genogroups G2 and G3 of CIAV.

Tissue Tropism of Chicken Anaemia Virus in Naturally Infected Broiler Chickens

Chicken anaemia virus (CAV) causes chicken infectious anaemia, a severe disease characterized by anaemia and immunosuppression and leading to serious economic losses in the poultry industry worldwide. Although CAV infection has been investigated under experimental conditions, information regarding natural infection is scarce. This report describes an outbreak of CAV infection in 18-day-old broiler chickens and investigates virus tropism in affected birds. Thymic atrophy, pale bone marrow, swelling of the legs and foot ulcers (gangrenous dermatitis) were the most common gross lesions. Severe lymphoid cell depletion in the thymic cortex and presence of intranuclear acidophilic inclusion bodies, depletion of haemopoietic cells in bone marrow and presence of lymphoid infiltrates in several organs were also observed. Immunohistochemical labelling demonstrated the CAV antigens VP1 and VP3 in several organs. The expression of both proteins was similar in the thymic cortex and in the bone marrow, the main target organs of CAV; however, VP3 expression was more abundant in the other organs. Labelling of serial sections showed that CD3⁺ T lymphocytes might be responsible for the dissemination of the virus from the thymus and bone marrow to other organs and that virus-induced apoptosis, mediated through caspase-3, occurred mainly in the thymus and bone marrow.

Characterization of full genome sequences of chicken anemia viruses circulating in Egypt reveals distinct genetic diversity and evidence of recombination

Chicken anemia virus (CAV) is one of the commercially important diseases of poultry worldwide. In Egypt, CAV has been reported to be a potential threat to the commercial poultry sectors. Hence, this study was aimed at isolation and full genomic analysis of CAVs circulating in chicken populations in different geographical location in Egypt. A total of 42 samples were collected from broiler chicken flocks in 9 governorates in Egypt from 12 to 42 days of age. The mortality rate observed among chickens was ranging from 3% to 22%. Nineteen out of 42 farms were found positive for the CAV genome by polymerase chain reaction (PCR). Full genome sequencing was conducted for 18 positive samples. Genetic analysis revealed a high similarity of >99% in 11 viruses with the vaccine strain Del-Ros; while the other seven samples shared close similarity to CAV field strains isolated from China, Taiwan, and Brazil. The data also indicated Q139 and Q144 amino acids substitutions among the VP1 of Egyptian field strains, which are known to be important in virus replication and spread. Phylogenetic analysis of the sequenced viruses (n = 18) based on either the full gene nucleotide sequence or VP1 coding sequence, suggested the circulation of four distinct genotypes in Egypt designated as group A, B, C and D. Moreover, evidence of recombination was detected among four Egyptian CAVs located within group A. The findings of this study succeeded to elucidate the epidemiological and genetic features of CAVs circulating in Egypt, and underscores the important of CAVs surveillance.

Faecal virome of healthy chickens reveals a large diversity of the eukaryote viral community, including novel circular ssDNA viruses

This study is focused on the identification of the faecal virome of healthy chickens raised in high-density, export-driven poultry farms in Brazil. Following high-throughput sequencing, a total of 7743 de novo-assembled contigs were constructed and compared with known nucleotide/amino acid sequences from the GenBank database. Analyses with blastx revealed that 279 contigs (4 %) were related to sequences of eukaryotic viruses. Viral genome sequences (total or partial) indicative of members of recognized viral families, including Adenoviridae, Caliciviridae, Circoviridae, Parvoviridae, Picobirnaviridae, Picornaviridae and Reoviridae, were identified, some of those representing novel genotypes. In addition, a range of circular replication-associated protein encoding DNA viruses were also identified. The characterization of the faecal virome of healthy chickens described here not only provides a description of the viruses encountered in such niche but should also represent a baseline for future studies comparing viral populations in healthy and diseased chicken flocks. Moreover, it may also be relevant for human health, since chickens represent a significant proportion of the animal protein consumed worldwide.

Molecular Survey of Respiratory and Immunosuppressive Pathogens Associated with Low Pathogenic Avian Influenza H9N2 Subtype and Virulent Newcastle Disease Viruses in Commercial Chicken Flocks

The study was carried out in 48 poultry flocks to elucidate the roles of various complicating pathogens involved along with Newcastle disease (ND)/ low pathogenic avian influenza (LPAI) outbreaks. Necropsy was conducted and samples were collected for the isolation of Newcastle disease virus (NDV), Influenza A virus, infectious bronchitis virus (IBV), pathogenic bacteria; molecular detection of infectious laryngotracheitis virus (ILTV), fowl adeno virus (FAV), chicken anaemia virus (CAV), Mycoplasma synoviae (MS) and Mycoplasma gallisepticum (MG). The isolation results confirmed that 18/48 flocks (37%) were positive for the presence of hemagglutinating agents. Out of 18 hemagglutination (HA) positive flocks, 11 flocks (61%) were positive for both avian influenza virus (AIV) and NDV; 4 flocks (22%) were positive for NDV; and 3 flocks (17%) were positive for AIV. Sequence analysis of hemagglutinin and neuraminidase genes of AIV revealed that all were belonging to LPAI-H9N2 subtype. Sequence analysis of F gene of NDV revealed that they belong to virulent type. The PCR results confirmed the presence of three to seven etiological agents (CAV, FAV, ILTV, MG, MS and avian pathogenic E. coli along with LPAI/NDV from all the 18 HA-positive flocks. The detection rate of triple, quadruple, quintuple, sextuple and sevenfold infections was 17% (3 flocks), 28% (5 flocks), 11%, (2 flocks) 28% (5 flocks) and 17% (3 flocks), respectively. In conclusion, the disease complex involved more than one pathogen, primarily resulting from the interplay between LPAI-H9N2 and NDV; subsequently this could be exacerbated by co-infection with other agents which may cause exacerbated outbreaks that may otherwise go undetected in field.

Transcriptomic Profiling of Virus-Host Cell Interactions following Chicken Anaemia Virus (CAV) Infection in an In Vivo Model

Chicken Anaemia Virus (CAV) is an economically important virus that targets lymphoid and erythroblastoid progenitor cells leading to immunosuppression. This study aimed to investigate the interplay between viral infection and the host's immune response to better understand the pathways that lead to CAV-induced immunosuppression. To mimic vertical transmission of CAV in the absence of maternally-derived antibody, day-old chicks were infected and their responses measured at various time-points post-infection by qRT-PCR and gene expression microarrays. The kinetics of mRNA expression levels of signature cytokines of innate and adaptive immune responses were determined by qRT-PCR. The global gene expression profiles of mock-infected (control) and CAV-infected chickens at 14 dpi were also compared using a chicken immune-related 5K microarray. Although in the thymus there was evidence of induction of an innate immune response following CAV infection, this was limited in magnitude. There was little evidence of a Th1 adaptive immune response in any lymphoid tissue, as would normally be expected in response to viral infection. Most cytokines associated with Th1, Th2 or Treg subsets were down-regulated, except IL-2, IL-13, IL-10 and IFNγ, which were all up-regulated in thymus and bone marrow. From the microarray studies, genes that exhibited significant (greater than 1.5-fold, false discovery rate <0.05) changes in expression in thymus and bone marrow on CAV infection were mainly associated with T-cell receptor signalling, immune response, transcriptional regulation, intracellular signalling and regulation of apoptosis. Expression levels of a number of adaptor proteins, such as src-like adaptor protein (SLA), a negative regulator of T-cell receptor signalling and the transcription factor Special AT-rich Binding Protein 1 (SATB1), were significantly down-regulated by CAV infection, suggesting potential roles for these genes as regulators of viral infection or cell defence. These results extend our understanding of CAV-induced immunosuppression and suggest a global immune dysregulation following CAV infection.