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

Molecular characterization and pathogenicity study of a highly pathogenic strain of chicken anemia virus that emerged in China

Chicken infectious anemia (CIA) is caused by chicken anemia virus (CAV). Recently, severe anemia has emerged in layer chickens (8 to 10-week-old) on poultry farms in China. However, the etiological characteristics and pathogenic potential of CAV in chickens at 6 weeks or older are not well understood. In this study, we isolated a CAV strain, termed SD15, from two-month-old chicken with severe anemia and analyzed the genetic evolution relationship. We found that strain SD15 had the highest homology (98.9%) with CAV18 strain. Comparison with 33 reference strains revealed 16 amino acid mutations in strain SD15, two of which were previously unknown (F210S in VP1 and L25S in Vp3). Compared with low pathogenic strains (Cux-1 and C14), highly pathogenic strains (SDLY08 and SD15) had three base mutations in their noncoding region. To further understand its pathogenicity, 10-week-old specific-pathogen-free (SPF) chickens were challenged with the novel strain and SDLY08. No obvious clinical symptoms were observed in the SDLY08 group. However, SD15-infected chickens showed significant growth retardation and immunosuppression. The main manifestations of immunosuppression were the significantly reduced thymus and bursa indices and AIV-H9 vaccine-induced antibody levels (P < 0.05). The lowest number of red blood cells in the SD15 group was just 60% of that in the control group. Taken together, the novel strain SD15 not only showed higher pathogenicity but also exhibited the potential ability to break the age resistance of older chickens to CAV. Our study enhanced the understanding of the epidemiological characteristics of chickens infected with severe anemia and can facilitate the development of improved control strategies of CIA in China.

Genomic Characterization of CIAV Detected in Contaminated Attenuated NDV Vaccine: Epidemiological Evidence of Source and Vertical Transmission From SPF Chicken Embryos in China

Live attenuated vaccines have been extensively used to prevent infectious disease in poultry flocks. Freedom from exogenous virus is a high priority for any veterinary vaccines. Recently, attenuated Newcastle disease virus (NDV) vaccines were detected to be contaminated with chicken infectious anemia virus (CIAV) in a routine screening for exogenous viruses. To investigate the possible source of the contamination, we conducted virological tests on a specific-pathogen-free (SPF) layer breeder flock that provide the raw materials for vaccines in this manufacturer. Firstly, CIAV antibodies in serum and egg yolks samples of the SPF laying hens were detected by ELISA assays. The results showed that CIAV antibodies in serum and egg yolks were 62% positive and 57% positive, respectively. Then, DNA was extracted from the NDV vaccines and SPF chicken embryonated eggs, and detected by molecular virology assays. The results showed that three assays for pathogens in embryonated eggs had similar positive rates (35.8%). And the sequences of CIAV from SPF embryos and NDV vaccines consisted of 2,298 nucleotides (nt) with 100% homology. The new full-length genome of CIAV was designated SDSPF2020 (Genbank accession number: MW660821). Data showed SDSPF2020 had the sequence similarities of 95.8–99.6% with reference strains, and shared the highest homology with the Chinese strain HLJ15125. These results strongly suggested that exogenous CIAV contamination is most likely caused by wild virus infection in SPF flocks and vertical transmission to chicken embryos. Collectively, this study illustrated that vertical transmission of CIAV from a SPF layer breeder flock to embryos was a non-neglible way for exogenous virus contamination in vaccine production.

Relevance of antibodies against the Chicken Anaemia Virus

Chicken Infectious Anaemia (CIA) Virus (CAV) inhibits the function of multiple immune compartments. Mortality due to clinical infection is controlled in broilers by passive immunization derived from vaccinated breeders. Therefore, serological tests are often used in chicks to determine maternally-derived antibodies (MDA). We used a vaccine overdose-induced model of CIA. The model replicated the most common features of the disease. This model was used to determine the role of MDA in the protection of chicks. Hatchlings were tested for anti-CAV titers by ELISA and were sorted into groups based on antibody levels. SPF chicks were used as a no-antibody control. Lower specific antibody levels seemed to facilitate viral entry into the thymus, but viral levels, CD4⁺ and CD8⁺ counts, thymus architecture, and haematocrit were preserved by MDA, regardless of its levels. Levels of MDA are not correlated with protection from CIA, but are important for the progression CAV infection.

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.

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.

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.

Study of dynamic of chicken infectious anaemia virus infection: which sample is more reliable for viral detection?

Chicken infectious anaemia virus (CIAV) is a widely distributed immunosuppressive agent. SPF flocks and eggs used for vaccine production and diagnostics must be CIAV-free. Detection of CIAV infection in SPF flocks involves primarily serology or other invasive methods. In order to evaluate different types of samples for rapid detection of CIAV infection, a trial was conducted in serologically negative broiler breeder pullets vaccinated with a commercial live-attenuated CIAV vaccine. Controls and vaccinated groups were sampled before and after vaccination. Invasive and non-invasive samples were used for CIAV DNA detection by real-time PCR. Seroconversion occurred at 14 days post-inoculation (DPI) in the vaccinated group, whereas CIAV genome was detected by qPCR at 7 DPI in both invasive and non-invasive samples. Only invasive samples remained qPCR positive for CIAV DNA by 21 DPI despite seroconversion of the chickens.

Pathological and immunohistochemical studies of subclinical infection of chicken anemia virus in 4-week-old chickens

Subclinical infection of chicken anemia virus (CAV) at 4 to 6 weeks of age, after maternal antibodies have waned, is implicated in several field problems in broiler flocks. In order to understand the pathogenesis of subclinical infection with CAV, an immunopathological study of CAV-inoculated 4-week-old SPF chickens was performed. Sixty 4-week-old SPF chickens were equally divided into CAV and control groups. The CAV group was inoculated intramuscularly with the MSB1-TK5803 strain of CAV. Neither mortality nor anemia was detected in the CAV and control groups. In the CAV group, no signs were observed, except that some chickens were grossly smaller compared with the control group. Sporadic thymus lobes appeared to be reddening and atrophied. Within the first two weeks p.i. of CAV, there was a mild to moderate depletion of lymphocytes in the thymus cortex and spleen in some chickens. Moreover, lymphoid depletion of the bursa of Fabricius, proventriculus and cecal tonsils was observed. Hyperplastic lymphoid foci were observed in the liver, lungs, kidneys and heart at the 4th week p.i. of CAV. Immunohistochemically, a moderate lymphoid depletion of CD4(+)and CD8(+) T cells in the thymus cortex and spleen was observed in some chickens within two weeks p.i. of CAV. CAV inclusions and antigens were detected infrequently in the thymus cortex and spleen. It could be concluded that the immunosuppression in subclinical infection with CAV occurs as a result of reduction of cellular immunity.

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.

Unraveling the puzzle of human anellovirus infections by comparison with avian infections with the chicken anemia virus

Current clinical studies on human annelloviruses infections are directed towards finding an associated disease. In this review we have emphasized the many similarities between human anellovirus and avian circoviruses and the cell and tissue types infected by these pathogens. We have done this in order to explore whether knowledge acquired from natural and experimental avian infections could reflect and be extrapolated to the less well-characterized human annellovirus infections. The knowledge gained from the avian system may provide suggestions for decoding the enigmatic human anellovirus infections, and finding the specific disease or diseases caused by these human anellovirus infections. Each additional parallelism between chicken anemia virus (CAV) and Torque teno virus (TTV) further strengthens this premise. As we have seen information from human infections can also be used to better understand avian infections as well. Increased attention must be focused on the "hidden" or unrecognized, seemingly asymptomatic effects of circovirus and anellovirus infections. Understanding the facilitating effect of these infections on disease progression caused by other pathogens may help to explain differences in outcome of complicated poultry and human diseases. The final course of a pathogenic infection is determined by variations in the state of health of the host before, during and after contact with a pathogen, in addition to the phenotype of the pathogen and host. The health burden of circoviridae and anellovirus infections may be underestimated, due to lack of awareness of the need to search past the predominant clinical effect of identified pathogens and look for modulation of cellular-based immunity caused by co-infecting circoviruses, and by analogy, human anneloviruses.

The contribution of feathers in the spread of chicken anemia virus

Chicken anemia virus (CAV) spreads vertically and horizontally, however, the process is mostly still obscure. To further clarify the horizontal CAV spread, we examined the contribution of feathers. We demonstrated that CAV could be amplified from DNA purified from feather shafts of experimentally infected chicks, and the process efficacy was evaluated by comparing the amplification of DNA purified from feather shafts and lymphoid organs of CAV-experimentally infected chicks. DNA from feathers was found as an efficient source for CAV detection. Further, to substantiate whether CAV reaches the feather shafts passively via the blood, or intrinsically, causing histopathological changes, the feather follicle tissues were examined for CAV-induced lesions. Specific histological changes were found, however, immunohistochemistry failed to detect viral proteins. To determine whether the feather shafts are a source of infective virus, they were homogenized and used to infect 1-day-old chicks via the mucosal entries (eyes, nose and oropharynx). That infection mode simulates the natural route of horizontal infection in commercial poultry houses. We demonstrated the CAV-infection by serology, virology and pathology, showing that feather shafts carry infectious CAV either on their surface or within their feather pulp, and concluded that feathers contribute to the horizontal CAV dissemination.