Viral load in 1-day-old and 6-week-old chickens infected with chicken anaemia virus by the intraocular route

Development of TaqMan Real-Time Polymerase Chain Reaction Assay for Detection of Chicken Anemia Virus in Newcastle Disease Vaccines

Exogenous chicken anemia virus (CAV) has been detected in commercial poultry vaccines in various countries of the world. The presence of unwanted CAV in vaccines not only influences the epidemiology of chicken infectious anemia disease, but may also lead to vaccine failure and confusing results when vaccine responses are monitored. To detect CAV in contaminated vaccines, nucleic acid testing (unlike conventional testing) has a shorter processing time and does not require cell culture or live animals. The aim of the current study was to develop a TaqMan real-time polymerase chain reaction (PCR) assay to detect and quantify CAV in poultry vaccines and investigate CAV contamination in Razi live Newcastle disease vaccines. The TaqMan real-time PCR assay was set up, optimized, and validated in successive experiments. A standard plasmid pUC-VP2 containing viral protein 2 of CAV was constructed and used in the assay to generate a standard curve to quantify CAV genomes. A clear linear correlation was observed between threshold cycle (Ct) values and plasmid copy numbers in the amplification plots of 10-fold serial dilution of the plasmid. Total DNA of three samples of each of four different Razi live Newcastle disease vaccines, namely LaSota, B1, clone.12IR, and thermo-resistant strains, were extracted and subjected to real-time PCR assay. No CAV contamination was detected in the Razi Live Newcastle vaccines. The developed TaqMan real-time PCR assay provides a quick, specific, and sensitive method for use in detecting CAV in quality control vaccine testing and viral load studies.

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.

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.

Persistent Infection with Chicken Anemia Virus in 3-Week-Old Chickens Induced by Inoculation of the Virus by the Natural Route

Naturally acquired chicken anemia virus (CAV) infection in chickens frequently occurs from 3 weeks of age onward after maternally derived antibodies have decayed. The oral inoculation of older chickens with CAV was reported to have negative effects on cell-mediated immune function, and pathological changes were identified. To date, there has been no complete illustration of an immunological and persistent infection. To understand the pathogenesis of persistent CAV infection, an immunological study of CAV-infected 3-week-old specific pathogen-free (SPF) chickens was carried out by different routes of inoculation. The weight, packed cell volumes, and organ samples were obtained at 7, 14, 21, and 28 days postinfection (dpi). Here, we compared hematological, immunological, and sequential pathological evaluations and determined the CAV tissue distribution in different organs. Neither a reduction in weight gain nor anemia was detected in either the inoculated or the control group. The immune-pathological changes were investigated by evaluating the body and thymus weight ratio and specific antibody titer. Delayed recovery of the thymus corresponding to a low antibody response was detected in the orally inoculated group. This is different from what was found in chickens intramuscularly infected with the same dose of CAV. The CAV remaining in a wide range of tissues was examined by viral reisolation into cell culture. The absence of the virus in infected tissues was typically found in the intramuscularly inoculated group. These chickens were immediately induced for a protective antibody response. A few viruses replicating in the thymus were found 21 dpi due to the regression in the antibody titer in the orally inoculated group. Our findings support that a natural infection with CAV may lead to the gradual CAV viral replication in the thymus during inadequate antibody production. The results clearly confirmed that virus-specific antibodies were essential for viral clearance. Under CIA-risk circumstances, administration of the CAV vaccine is important for achieving a sufficient protective immune response.

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.

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

Chicken anemia virus (CAV) is one the important pathogen affecting commercial poultry sector globally by causing mortality, production losses, immunosuppression, aggravating co-infections and vaccination failures. Here, we describe the effects of CAV load on hematological, histopathological and immunocytochemical alterations in 1-day old infected chicks. The effects of CAV on cytokine expression profiles and generation of virus specific antibody titer were also studied and compared with viral clearance in various tissues. The results clearly confirmed that peak viral load was achieved mainly in lymphoid tissues between 10 and 20 days post infection (dpi), being highest in the blood (log1010.63 ±0.87/ml) and thymus (log1010.29 ±0.94/g) followed by spleen, liver, bone marrow and bursa. The histopathology and immunoflowcytometric analysis indicated specific degeneration of T lymphoid cells in the thymus, spleen and blood at 15 dpi. While the transcript levels of interleukin (IL)-1, IL-2, IL-12 decreased at all dpi, interferon (IFN)-γ increased (3-15 fold) during early stages of infection and the appearance of virus specific antibodies were found to be strongly associated with virus clearance in all the tissues. Our findings support the immunosuppressive nature of CAV and provide the relation between the virus load in the various body tissues and the immunopathological changes during clinical CAV infections.

Latent porcine circovirus type 2-infected domestic pigs: A potential infection model for the effective development of vaccines against latent or chronic virus induced diseases

Until recently, knowledge of the pathogenicity of Circoviridae and Anelloviridae family members was limited. Our previous discoveries provided clues toward resolving this issue based on studies of the latent nature of porcine circovirus type 2 (PCV2) genotype group members. We developed a conventional pig infection model that indicated that weaners already harbored latent PCV2 infection in the thymus, which enabled the viruses to specifically modulate the maturation of T-helper cells. This finding raised the possibility that the thymi of normal fetuses were already infected with PCV2. The present findings further substantiate our hypothesis that PCV2 masquerades as the host by infecting fetuses before they acquire immune-competence. We provide the first demonstration that all domestic pig fetuses preferentially harbor latent PCV2-infected cells in their thymi. These PCV2-infected cells are different from thymocytes and are located in the medulla of the fetal thymus. These latent PCV2-infected cells in fetuses are found at the same location and share characteristics with the infected cells observed in adolescent pigs. Moreover, fetuses also harbor these infected cells in other lymph system organs. We provide the first demonstration that the fetal thymus virus pools are minimally affected by sow vaccination, highlighting the immune-privileged character of this organ. Furthermore, we found a striking reduction in virus-infected cells in the fetal spleen and an increase in PCV2-infected cells in the fetal intestine of anti-PCV2-vaccinated mothers. These data indicate that specific immune response interactions occur between mothers and their progeny that are not dependent on the humoral immunity of the mother and cannot be attributed to the rudimentary humoral responses of the fetuses because these pig fetuses do not have any PCV2-specific antibodies. These shifts in our understanding of the PCV2-infected cell pool will lead to different avenues in the search for effective vaccination strategies against latent and chronic pathogens.

Chronological analysis of gross and histological lesions induced by field strains of fowl adenovirus serotypes 1, 8b and 11 in one-day-old chickens

Fowl adenoviruses (FAdVs) cause diseases in domestic chickens, including inclusion body hepatitis (IBH), with immunosuppression believed to play a role in their pathogenesis. To gain a better understanding of the pathogenesis and chronology of disease caused by FAdVs, the gross pathology, histopathology and dissemination of virus were examined at several different time points, after inoculation of one-day-old specific pathogen-free chickens with FAdV-1, FAdV-8b or FAdV-11 via the ocular route. FAdV-8b had a slightly greater virulence than FAdV-11, but both were primary pathogens. The presence and severity of hepatic lesions were used to define the three stages of the disease: incubation (1-3 days post-inoculation, PI), degeneration (4-7 days PI) and convalescence (14 days PI). Both viruses were detected in the liver, kidney, bursa, thymus and gizzard of most birds during the degenerative stage, and persisted in the gizzard into convalescence. The FAdV-1 isolate was found to be apathogenic, but virus was detected in the bursa and/or gizzard of several birds between 2 and 7 days PI. This is the first study examining the chronology of gross and microscopic lesions of pathogenic and apathogenic FAdVs in association with viral presence in multiple tissues. It was concluded that both FAdV-8b and FAdV-11 are primary pathogens, and that these strains may play a role in immunosuppression.

Assessing the efficacy of an inactivated chicken anemia virus vaccine

BACKGROUND

Chicken anemia virus (CAV) is an immunosuppressive virus that causes chicken infectious anemia (CIA) which is a highly contagious avian disease. CAV causes major economic losses in the poultry industry worldwide. The current CAV vaccine is a live attenuated strain administered in the drinking water that risks horizontal infection of other chickens. The purpose of this study was to develop a novel vaccine against CAV that can be administered safely using a highly pathogenic isolate inactivated with β-propiolactone hydrolysis that would protect chicks from CAV.

METHODS

Hens were vaccinated twice intramuscularly with a novel CAV GD-G-12 inactivated vaccine and the humoral immune responses of the hens and offspring were monitored by ELISA. A heterologous intramuscular challenge using the CAV strain GD-E-12 was conducted in the chicks hatched from vaccinated or unvaccinated hens.

RESULTS

The vaccine strain, GD-G-12, was shown to be highly pathogenic prior to inactivation evidenced by thymic atrophy and bleeding, and weight loss. The inactivated vaccine was considered safe and showed no signs of pathogenicity. High titers of CAV specific antibodies were detected in the vaccinated hens and in their chicks, indicating vertical transfer of maternal antibodies. Furthermore, the chicks hatched from vaccinated hens were resistant to a heterologous CAV challenge and showed no signs of weight loss and thymic atrophy and bleeding.

CONCLUSION

Our studies are proof of principle that inactivated GD-G-12 might be a novel vaccine candidate to prevent CAV infection, and highlight the utility of using an inactivated virus for this vaccine.

Application of high-resolution melting curve analysis for typing of fowl adenoviruses in field cases of inclusion body hepatitis

OBJECTIVE

Fowl adenoviruses (FAdVs) cause inclusion body hepatitis (IBH) in chickens. In this study, clinical cases of IBH from Australian broiler flocks were screened for the presence and genotype of FAdVs.

METHODS

Twenty-six IBH cases from commercial poultry farms were screened. Polymerase chain reaction (PCR) coupled with high-resolution melt (HRM) curve analysis (PCR/HRM genotyping) was used to determine the presence and genotype of FAdVs. For comparison, field isolates were also assessed by virus microneutralisation and nucleotide sequence analysis of the hexon loop 1 (Hex L1) gene. PCR detection of chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) was also employed.

RESULTS

FAdV-8b and FAdV-11 were identified in 13 cases each. In one case, FAdV-1 was also identified. Cross-neutralisation was observed between the FAdV-11 field strain and the reference FAdV-2 and 11 antisera, a result also seen with the type 2 and 11 reference FAdVs. Field strains 1 and 8b were neutralised only by their respective type antisera. The FAdV-8b field strain was identical to the Australian FAdV vaccine strain (type 8b) in the Hex L1 region. The Hex L1 sequence of the FAdV-11 field strain had the highest identity to FAdV-11 (93.2%) and FAdV-2 (92.7%) reference strains. In the five cases tested for CAV and IBDV, neither virus was detected. The evidence suggested the presence of sufficient antibodies against CAV and IBD in the parent flocks and there was no indication of immunosuppression caused by these viruses.

CONCLUSION

These results indicate that PCR/HRM genotyping is a reliable diagnostic method for FAdV identification and is more rapid than virus neutralisation and direct sequence analysis. Furthermore, they suggest that IBH in Australian broiler flocks is a primary disease resulting from two alternative FAdV strains from different species.

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.