Impact of virus load on immunocytological and histopathological parameters during clinical chicken anemia virus (CAV) infection in poultry

Recombinant Marek's disease virus expressing VP1 and VP2 proteins provides robust immune protection against chicken infectious anemia virus

Chicken infectious anemia (CIA) is a highly contagious disease caused by the chicken infectious anemia virus (CIAV), and it poses a serious threat to the poultry industry. However, effective control measures and strategies have not been identified. In this study, a recombinant Marek's disease virus (rMDV) expressing the VP1 and VP2 proteins of CIAV was successfully constructed using CRISPR/Cas9, and a commercial Marek's disease virus (MDV) vaccine strain was used as the vector. VP1 and VP2 expression by rMDV was confirmed by immunofluorescence assay and western blot analysis, which revealed robust in vitro expression. Further analysis showed that the VP1 and VP2 genes integrated into the MDV genome did not alter the growth kinetics of the virus and remained stable even after 20 passages, indicating the genetic stability of the recombinant virus. In animal studies, vaccination of one-day-old specific-pathogen-free chickens with rMDV induced high levels of CIAV-specific antibodies (1 × 105) and neutralizing antibodies (1:25) and a potent cellular immune response. Moreover, rMDV vaccination conferred an 85% protective index against challenge with a highly virulent strain of CIAV, significantly reducing the occurrence of anemia and thymic atrophy caused by CIAV infection and dramatically suppressing CIAV replication in the thymus. Collectively, these results highlight the potential of rMDV as a vaccine candidate for preventing and controlling CIAV infection, thus offering a new avenue for mitigating the impact of CIA on the poultry industry.

Beak and feather disease virus (BFDV) persists in tissues of asymptomatic wild Crimson Rosellas

Infectious diseases can drive populations and species to extinction. Beak and feather disease virus (BFDV) is a circovirus of global conservation concern that can infect all Psittaciformes and some other species. Yet some parrot species, such as Crimson rosellas (Platycercus elegans), can live successfully with high BFDV prevalence (>40%) with no clinical signs reported in infected individuals. We assessed BFDV load in 10-12 tissues per bird, from n = 66 P. elegans, to reveal tissue tropism and BFDV persistence in tissues. Here we show that in 94% of individuals, BFDV was detected in one or more tissues. While BFDV replicated to high levels in subadults, in adults (some confirmed seropositive) the virus persisted in various tissues at much lower levels. Our findings reveal that BFDV is much more common in wild P. elegans than previously thought and suggest that current screening practices (mostly on blood) may substantially underestimate BFDV infection estimates, with implications for biosecurity and conservation programs globally.

Effects of garlic, onion, and apple cider vinegar as a herbal mixture on performance and blood traits of broilers inoculated with chicken infectious anemia virus

This study assessed the effects of a herbal mixture (HM) to protect poultry against chicken infectious anemia (CIA) and to modulate the adverse effects of this virus on performance, mortality, blood profile, white blood cells (WBCs) count, liver enzymes, liver histopathology, and intestinal morphology. Therefore, 240 one-day-old male broiler chicks (Ross 308) were divided into four experimental groups, with six replicates and ten chicks per group. The experimental groups consisted of a control group and groups with 2.5%, 5%, and 7.5% HM, all based on corn-soybean meal. All chicks were inoculated with the CIA virus (CIAV) on day 7. The results showed that supplementation of 2.5% of HM to broiler diet increased feed intake (FI) (P < 0.05) and also increased body weight (BW) and weight gain (WG) slightly (P > 0.05). Adding 7.5% HM caused a reversible decrease in FI, BW, and WG and increased FCR. Compared with the control group, mortality rates declined with an additional dose of HM in CIAV-infected chickens. HM supplementation in the diet of CIAV-infected chickens increased hematocrit (HCT), hemoglobin (Hb), and mean corpuscular volume (MCV) and decreased mean corpuscular hemoglobin concentration (MCHC) compared to the control (P < 0.05). Lymphocyte percentage and lymphocyte/heterophile ratio increased in HM-supplemented groups, especially at 2.5% (P < 0.05), and heterophile and granulocyte percentages were reduced (P < 0.05). Liver enzyme alkaline phosphatase (ALP) and liver steatosis declined in the 2.5% HM-treated group compared to the control (P < 0.05). It was concluded that adding 2.5% of the HM to the CIAV-infected broiler's diet did not negatively affect chicken performance. In addition to its hypolipidemic effects, it could prevent HCT and Hb from decreasing in chicks infected with CIAV and positively affect leukocyte types and liver enzymes. Interestingly, an additional dose of HM in the diet of the CIAV-infected broilers reduced mortality. Therefore, adding 2.5% of HM could prevent the adverse effects of CIA on hematological traits in broiler chicken flocks without adverse effects on performance.

Chicken anemia virus VP1 negatively regulates type I interferon via targeting interferon regulatory factor 7 of the DNA-sensing pathway

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway plays a vital role in sensing viral DNA in the cytosol, stimulating type I interferon (IFN) production and triggering the innate immune response against DNA virus infection. However, viruses have evolved effective inhibitors to impede this sensing pathway. Chicken anemia virus (CAV), a nonenveloped ssDNA virus, is a ubiquitous pathogen causing great economic losses to the poultry industry globally. CAV infection is reported to downregulate type I IFN induction. However, whether the cGAS-STING signal axis is used by CAV to regulate type I IFN remains unclear. Our results demonstrate that CAV infection significantly elevates the expression of cGAS and STING at the mRNA level, whereas IFN-β levels are reduced. Furthermore, IFN-β activation was completely blocked by the structural protein VP1 of CAV in interferon stimulatory DNA (ISD) or STING-stimulated cells. VP1 was further confirmed as an inhibitor by interacting with interferon regulatory factor 7 (IRF7) by binding its C-terminal 143-492 aa region. IRF7 dimerization induced by TANK binding kinase 1 (TBK1) could be inhibited by VP1 in a dose-dependent manner. Together, our study demonstrates that CAV VP1 is an effective inhibitor that interacts with IRF7 and antagonizes cGAS-STING pathway-mediated IFN-β activation. These findings reveal a new mechanism of immune evasion by CAV.

Genomic Sequence and Pathogenicity of the Chicken Anemia Virus Isolated From Chicken in Yunnan Province, China

Chicken anemia virus (CAV), which has been reported in many countries, causes severe anemia and immunosuppression in chickens. In this study, a CAV strain YN04 belonging to genotype A was first identified from infected chickens in Yunnan province, China. Moreover, the animal infection experiments further confirmed that the strain YN04 is a highly pathogenic strain, which can cause 86.67% mortality in chickens in the infection group. The mean death time of infected chickens was 13.1 days post infection (dpi). CAV infection induced severe anemia with significant decrease in packed cell volume (PCV), and serious atrophy and lesion of thymus and bursa with high viral load at 14 dpi. Besides, CAV infection caused a sharp decrease in chicken body weight and immune organ indices including the ratio of thymus or bursa to body weight at 21 dpi, which displayed the potential immunosuppression state at this stage. These findings enrich the epidemiological data on CAV and may provide information for preventing its further spread in Yunnan province, China.

Newcastle Disease Virus Vectored Chicken Infectious Anaemia Vaccine Induces Robust Immune Response in Chickens

Newcastle disease virus (NDV) strain R2B, with an altered fusion protein cleavage site, was used as a viral vector to deliver the immunogenic genes VP2 and VP1 of chicken infectious anaemia virus (CIAV) to generate a bivalent vaccine candidate against these diseases in chickens. The immunogenic genes of CIAV were expressed as a single transcriptional unit from the NDV backbone and the two CIA viral proteins were obtained as separate entities using a self-cleaving foot-and-mouth disease virus 2A protease sequence between them. The recombinant virus (rR2B-FPCS-CAV) had similar growth kinetics as that of the parent recombinant virus (rR2B-FPCS) in vitro with similar pathogenicity characteristics. The bivalent vaccine candidate when given in specific pathogen-free chickens as primary and booster doses was able to elicit robust humoral and cell-mediated immune (CMI) responses obtained in a vaccination study that was conducted over a period of 15 weeks. In an NDV and CIAV ELISA trial, there was a significant difference in the titres of antibody between vaccinated and control groups which showed slight reduction in antibody titre by 56 days of age. Hence, a second booster was administered and the antibody titres were maintained until 84 days of age. Similar trends were noticed in CMI response carried out by lymphocyte transformation test, CD4⁺ and CD8⁺ response by flow cytometry analysis and response of real time PCR analysis of cytokine genes. Birds were challenged with virulent NDV and CIAV at 84 days and there was significant reduction in the NDV shed on the 2nd and 4th days post challenge in vaccinated birds as compared to unvaccinated controls. Haematological parameters comprising PCV, TLC, PLC and PHC were estimated in birds that were challenged with CIAV that indicated a significant reduction in the blood parameters of controls. Our findings support the development and assessment of a bivalent vaccine candidate against NDV and CIAV in chickens.

Effective production of recombinant Δ60VP1 chicken anemia virus protein in Escherichia coli and its application to a serodiagnostic indirect ELISA

Chicken anemia virus (CAV) causes severe anemia and immunosuppression in chickens. VP1 is the main capsid protein, and is suitable for diagnostic kit development, however, it has 24 arginine residues in the first forty N-terminal amino acids of the protein causing toxicity to bacteria leading to reduced prokaryotic expression. In this study, a 60 amino acid N-terminally truncated VP1 (Δ60VP1) which removes the toxic region was expressed in Escherichia coli and the resultant insoluble recombinant protein was purified by Ni-NTA affinity chromatography with anionic denaturing detergents. The high amounts of purified Δ60VP1 produced (150 mg/L) retained appropriate antigenicity and the antigen was used to develop an indirect enzyme-linked immunosorbent assay (ELISA) for serological diagnosis of CAV. One hundred fifty-two chicken serum samples (n = 152) were evaluated using the newly developed Δ60VP1 indirect ELISA (cutoff value = 7.58 % S/P). The sensitivity and specificity of the Δ60VP1 indirect ELISA were 87.50 % and 95.31 %, respectively, while the agreement between the Δ60VP1 indirect ELISA and the commercial IDEXX CAV ELISA was 90.79 % (kappa = 0.814). In this study, we have developed an alternative VP1 production platform in E. coli by truncating the N-terminal 60 amino acids (Δ60VP1) and using anionic denaturing detergents during the purification to successfully solubilize the insoluble Δ60VP1. The antigen was purified with high yield and good immunoreactivity, and an indirect ELISA was developed. The assay could potentially be applied to large-scale CAV serosurveillance.

Pathological and virological analysis of concurrent disease of chicken anemia virus infection and infectious bronchitis in Japanese native chicks

A concurrent infection of chicken anemia virus (CAV) and infectious bronchitis virus (IBV) was detected in Japanese native chicks in 2017, in which a high mortality rate (97.7%) was recorded in a small flock of 130 chicks exhibiting poor growth. Histological examination revealed that the affected chicks exhibited two different pathological entities: one was severe hematopoietic and lymphocytic depletion with abnormally large cells containing intranuclear inclusion bodies of CAV, whereas the other was renal tubular necrosis due to IBV infection. Immunohistochemistry detected CAV antigens in the bone marrow, liver, and spleen as well as IBV antigens in the kidneys, trachea, and air sacs. CAV was isolated from the liver sample of the chicks, and the isolated strain was designated as CAV/Japan/HS1/17. A phylogenetic analysis of the CAV VP1 gene revealed that CAV/Japan/HS1/17 is genetically similar to Chinese strains collected from 2014 to 2016. An experimental infection was performed using CAV/Japan/HS1/17 and specific-pathogen-free chicks to determine the pathogenicity of CAV/Japan/HS1/17. The isolate caused 100% anemia and 70% mortality to chicks inoculated at one day old, 80% of chicks inoculated at seven days old also developed anemia, and 10% died from CAV infection. These results suggest that the unusually high mortality in Japanese native chicks can be attributed to dual infection with both CAV and IBV. The results of the experimental infection suggest that CAV/Japan/HS1/17 has a pathogenic potential to specific-pathogen-free chicks and a relatively higher pathogenicity than previous Japanese CAV strains.

Oral Inoculation of Specific-Pathogen-Free Chickens with Chicken Anemia Virus Induces Dose-Dependent Viremia and Transient Anemia

Chicken infectious anemia caused by chicken anemia virus (CAV) is a very important immunosuppressive disease in chickens. The horizontal spread of CAV in field chickens has been confirmed mainly through oral infection in our published article. Anemia is the main symptom of this disease. Studies by other scientists have shown that infection of CAV in 1-day-old chicks can cause anemia, and the degree of anemia is directly proportional to the dose of infectious virus. However, the pathogenesis of oral inoculation of CAV in older chickens is still not well understood. The purpose of this study was to determine whether 3-weeks-old specific-pathogen-free (SPF) chickens infected with different viral doses in oral route would cause anemia, as well as other signs associated with age-resistance. The experimental design was divided into a high-dose inoculated group (10⁶ 10₅₀), low-dose inoculated group (10³ TCID₅₀), and non-virus inoculated control group, and 12 birds in each group at the beginning of the trial. The packed cell volumes (PCVs), CAV genome copies in tissues, CAV titer in peripheral blood fractions, and serology were evaluated at 7, 14, and 21 days post-infection (dpi). Virus replication and spread were estimated using quantitative polymerase chain reaction (qPCR) and viral titration in cell culture, respectively. The results showed that the average PCVs value of the high-dose inoculated group was significantly lower than that of the control group at 14 dpi (p < 0.05), and 44.4% (4/9) of the chickens reached the anemia level (PCVs < 27%). At 21 dpi, the average PCV value rebounded but remained lower than the control group without significant differences. In the low-dose inoculated group, all birds did not reach anemia during the entire trial period. Peripheral blood analysis showed that the virus titer in all erythrocyte, granulocyte and mononuclear cell reached the peak at 14 dpi regardless of the high-dose or low-dose inoculated group, and the highest virus titer appeared in the high-dose inoculated group of mononuclear cell. In the low-dose inoculated group, CAV was detected only at 14 dpi in erythrocyte. Taken together, our results indicate that the older birds require a higher dose of infectious CAV to cause anemia after about 14 days of infection, which is related to apoptosis caused by viral infection of erythrocytes. In both inoculated groups, the viral genome copies did not increase in the bone marrow, which indicated that minimal cell susceptibility to CAV was found in older chickens. In the low-dose inoculated group, only mononuclear cells can still be detected with CAV at 21 dpi in seropositive chickens, indicating that the mononuclear cell is the target cell for persistent infection. Therefore, complete elimination of the CAV may still require the aid of a cell-mediated immune response (CMI), although it has previously been reported to be inhibited by CAV infection. Prevention of early exposure to CAV could be possible by improved hygiene procedures.

Virus-Induced Immunosuppression in Chickens

A healthy immune system is a cornerstone for poultry production. Any factor diminishing the immune responses will affect production parameters and increase cost. There are numerous factors, infectious and noninfectious, causing immunosuppression (IS) in chickens. This paper reviews the three viral diseases that most commonly induce IS or subclinical IS in chickens: Marek's disease virus (MDV), chicken infectious anemia virus (CIAV), and infectious bursal disease virus (IBDV), as well as the interactions among them. MDV-induced IS (MDV-IS) affects both humoral and cellular immune responses. It is very complex, poorly understood, and in many cases underdiagnosed. Vaccination protects against some but not all aspects of MDV-IS. CIAV induces apoptosis of the hemocytoblasts resulting in anemia, hemorrhages, and increased susceptibility to bacterial infections. It also causes apoptosis of thymocytes and dividing T lymphocytes, affecting T helper functions, which are essential for antibody production and cytotoxic T lymphocyte (CTL) functions. Control of CIAV is based on vaccination of breeders and maternal antibodies (MAbs). However, subclinical IS can occur after MAbs wane. IBDV infection affects the innate immune responses during virus replication and humoral immune responses as a consequence of the destruction of B-cell populations. Vaccines with various levels of attenuation are used to control IBDV. Interactions with MAbs and residual virulence of the vaccines need to be considered when designing vaccination plans. The interaction between IBDV, CIAV, and MDV is critical although underestimated in many cases. A proper control of IBDV is a must to have proper humoral immune responses needed to control CIAV. Equally, long-term control of MDV is not possible if chickens are coinfected with CIAV, as CIAV jeopardizes CTL functions critical for MDV control.

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.

Viruses with Circular Single-Stranded DNA Genomes Are Everywhere!

Circular single-stranded DNA viruses infect archaea, bacteria, and eukaryotic organisms. The relatively recent emergence of single-stranded DNA viruses, such as chicken anemia virus (CAV) and porcine circovirus 2 (PCV2), as serious pathogens of eukaryotes is due more to growing awareness than to the appearance of new pathogens or alteration of existing pathogens. In the case of the ubiquitous human circular single-stranded DNA virus family Anelloviridae, there is still no convincing direct causal relation to any specific disease. However, infections may play a role in autoimmunity by changing the homeostatic balance of proinflammatory cytokines and the human immune system, indirectly affecting the severity of diseases caused by other pathogens. Infections with CAV (family Anelloviridae, genus Gyrovirus) and PCV2 (family Circoviridae, genus Circovirus) are presented here because they are immunosuppressive and affect health in domesticated animals. CAV shares genomic organization, genomic orientation, and common features of major proteins with human anelloviruses, and PCV2 DNA may be present in human food and vaccines.

Immunomodulatory and prophylactic efficacy of herbal extracts against experimentally induced chicken infectious anaemia in chicks: assessing the viral load and cell mediated immunity

Chicken infectious anaemia virus (CIAV) is an economically important and a highly immunosuppressive virus affecting poultry industry worldwide. In this study we assessed the immunomodulatory effects of four herbal preparations namely Withania somnifera, Tinospora cordifolia, Azadirachta indica and E Care Se Herbal in resisting the viral multiplication and immunosuppression inflicted by CIAV in chicks. Day-old chicks (n = 90) were randomly and equally divided into six groups (Groups A-F). Groups A-D were administered with purified extracts of W. somnifera, T. cordifolia, A. indica and E Care Se Herbal, respectively followed by the evaluation of viral load in lymphoid organs by quantitative real-time PCR and cell mediated immune response by flow cytometric analysis of CD4⁺ and CD8⁺ T cells. Groups A-D were found to resist CIAV multiplication and pathogenesis with significant reduction of viral load compared with the infected control (P < 0.05). Group A-C chicks showed significantly higher (P < 0.05) CD4⁺ and CD8⁺ T cell counts compared to control birds while of E Care Se Herb had minimal effect on T cell count. The findings suggested that the herbal preparations used during the study were effective as both prophylactic and immunomodulatory agents and thus have potential of being used against CIAV induced immunosuppression in poultry.