Recombinant fiber-1 protein of fowl adenovirus serotype 4 induces high levels of neutralizing antibodies in immunized chickens

Virulent fowl adenovirus serotype 4 (FAdV-4) causes hydropericardium syndrome (HPS) with high mortality in chickens, leading to significant economic losses to the poultry industry. The development of an effective vaccine is essential for successful disease control. Here, we produced recombinant fiber-1 protein of FAdV-4, isolated from a Japanese HPS outbreak strain, JP/LVP-1/96, using a baculovirus expression system and evaluated its immunogenicity and protective efficacy. Recombinant fiber-1 protein induced high levels of neutralizing antibodies in immunized chickens, which were maintained for a minimum of 10 weeks. After being challenged with the virulent FAdV-4 strain JP/LVP-1/96, the immunized chickens did not exhibit clinical signs of infection or histopathological changes, there was a significant reduction in the viral load in various organs and total serum proteins, and albumin levels did not decline. These results suggest that the recombinant fiber-1 protein produced in this study can serve as a subunit vaccine to control HPS in chickens.

β-catenin facilitates fowl adenovirus serotype 4 replication through enhancing virus-induced autophagy

β-catenin is a key component of the Wnt/β-catenin signal transduction cascade which is a highly conserved signaling pathway in eukaryotes. Increasing evidence suggests that the Wnt/β-catenin signaling pathway is involved in the infection of many viruses. However, its role in fowl adenovirus serotype 4 (FAdV-4) replication remains unclear. In the present study, we showed that FAdV-4 infection increased the expression of β-catenin and promoted the nuclear translocation of β-catenin. Overexpression of β-catenin and LiCl treatment stimulated the accumulation of β-catenin in the nucleus, and then facilitated FAdV-4 replication. Conversely, repression of β-catenin by inhibitors and siRNA significantly inhibited FAdV-4 replication. Furthermore, inhibition of autophagy by 3-Methyladenine (3-MA) suppressed the FAdV-4 replication, and repression of β-catenin inhibited the FAdV-4-triggered autophagy. In conclusion, the nuclear translocation of β-catenin benefits FAdV-4 replication, and suppression of β-catenin limits FAdV-4 production by inhibiting FAdV-4-induced autophagy. These findings indicated that β-catenin is an important regulator of FAdV-4 replication which can serve as a potential target for anti-FAdV-4 agents.

Oral immunization of recombinant Saccharomyces cerevisiae expressing fiber-2 of fowl adenovirus serotype 4 induces protective immunity against homologous infection

Hydropericardium-hepatitis syndrome (HHS) caused by fowl adenovirus (FAdV) serotype 4 strains is a highly contagious disease that causes significant economic loss to the global poultry industry. However, subunit vaccine against FAdV-4 infection is not yet commercially available to date. This study aims to explore the potential for oral immunization of recombinant Saccharomyces cerevisiae expressing Fiber-2 of FAdV-4 as a subunit vaccine. Here, we constructed recombinant S. cerevisiae (ST1814G/Fiber-2) expressing recombinant Fiber-2 (rFiber-2), which was displayed on the cell surface. To evaluate the immune response and protective effect of live recombinant S. cerevisiae, chickens were orally immunized with the constructed live ST1814G/Fiber-2, three times at 5-day intervals, and then challenged with FAdV-4. The results showed that oral administration of live ST1814G/Fiber-2 could stimulate the production of humoral immunity, enhance the body's antiviral activity and immune regulation ability, improve the composition of gut microbiota, provide protection against FAdV-4 challenge, reduce viral load in the liver, and alleviate the pathological damage of heart, liver, and spleen for chicken. In addition, we found the synergistic effect in combining the ST1814G/Fiber-2 yeast and inactivated vaccine to trigger stronger humoral immunity and mucosal immunity. Our results suggest that oral live ST1814G/Fiber-2 is a potentially safer auxiliary preparation strategy in controlling FAdV-4 infection.

Genomic characterization of a fowl adenovirus serotype 4 strain isolated from a chicken with hydropericardium syndrome in Japan

Here, we report the genomic characterization of a fowl adenovirus serotype 4 strain isolated from a chicken with hydropericardium syndrome in Japan. The viral genome of FAdV-4 strain JP/LVP-1/96 was found to be 45,688 bp long. Amino acid substitutions at position 219 (G to D) in the fiber-2 protein and at position 188 (I to R) in the hexon protein, which are commonly found in virulent FAdV-4 strains, were also found in the JP/LVP-1/96 strain. Additional specific amino acid substitutions commonly found in virulent FAdV-4 strains were found in ORFs 4 and 43, which are present only in members of the species Fowl adenovirus C. Phylogenetic analysis based on complete hexon protein gene sequences showed that strain JP/LVP-1/96 belongs to a different genetic cluster from the strains circulating in neighboring countries.

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.

Identification of specific serotypes of fowl adenoviruses isolated from diseased chickens by PCR

We have developed a polymerase chain reaction (PCR) assay to facilitate detection of the major disease-associated serotypes of fowl adenovirus (FAdV) including serotypes 1, 2, 4, 8a and 8b; primers were designed based on serotype-specific sequences of the hexon gene. We tested field isolates from chickens diagnosed with inclusion body hepatitis, gizzard erosion and hydropericardium syndrome together with reference FAdV strains characterized in Japan. We found that the primers were serotype specific; appropriate amplification of serotype-specific hexon genes was confirmed by sequence analysis of the PCR products. This PCR assay will be useful for detection of FAdV and for differentiation between disease-associated serotypes.

Pathogenicity of a Jinding duck-origin cluster 2.1 isolate of Tembusu virus in 3-week-old Pekin ducklings

Tembusu virus (TMUV) infection most commonly affects breeder and layer ducks during laying period, and can also affect young ducks below 7 weeks of age. Here, we report our investigation of a TMUV-caused fatal disease of Jingding ducklings (Anas platyrhynchos domesticus) in Northeast China. The disease resulted in mortalities of up to 40 % in 2 to 4-week-old ducks, up to 25 % in 5 to 6-week-old ducks, and less than 10 % in 7 to 8-week-old ducks. Using a TMUV-specific reverse transcription-PCR assay, all 44 ducks collected from 10 different farms were found positive for TMUV. Phylogenetic analysis of the E nucleotide sequence revealed that five of the six TMUV strains detected from three young ducks and three laying ducks were grouped within cluster 2.1. Inoculation of the liver sample of a 40-day-old sick duck in BHK-21 cells resulted in isolation of cluster 2.1 TMUV strain H. In experimental infections performed using 3-week-old Pekin ducklings (Anas platyrhynchos domesticus) (n = 30; 10 birds/group), high mortality (60 %) was caused by strain H, in sharp contrast with a very low mortality (10 %) caused by strain Y which was isolated during outbreaks of the TMUV-related disease of young Jinding ducks in 2014 in the same region. These findings clearly demonstrated that the cluster 2.1 TMUV strain H is more pathogenic for 3-week-old ducklings as compared to the cluster 2.2 TMUV strain Y. The present study may enhance our understanding of pathogenicity of TMUV in young ducks, and will stimulate further studies on the pathogenesis of TMUV infection.

Pathogenic, Phylogenetic, and Serological Analysis of Group I Fowl Adenovirus Serotype 4 SDSX Isolated From Shandong, China

Hydropericardium hepatitis syndrome (HHS) caused by group I fowl adenovirus serotype 4 (FAdV-4) is an acute and infectious disease in fowl, particularly in broilers aged 3–5 weeks. In June 2015, a highly pathogenic disease outbroke in 25–40 day-old ducklings in Shandong province, characterized similar symptom to HHS. In order to determine the pathogenic mechanism of FAdV-4 (SDSX strain) in meat ducks. We divided 90 25-day-old Cherry Valley meat ducks into three groups (oral, subcutaneous, and control; 30 ducks in each group) and infected them with the virus. HHS, inclusion body hepatitis, and enlargement and hemorrhage of the spleen, kidney, lung, thymus, and brain were observed in FAdV-4-infected meat ducks. Histopathological changes were mainly characterized by severe fatty degeneration in the liver, basophilic inclusion bodies in hepatocytes, and vacuolation in the bursa. More importantly, viral DNA could be detected by quantitative real-time polymerase chain reaction in several viscera tissues (e.g., heart, liver, spleen) on the third day after infection. Notably, the livers of the two infected groups contained the highest concentration of viral DNA. In addition, immune responses were studied based on titer levels of the virus antibody and the levels of inflammatory cytokines interleukin (IL)-2 and interferon (IFN)-γ, and most levels were significantly upregulated, indicating that the host immune responses were activated early in infection. These findings increase our understanding of the pathogenicity of FAdV-4 (SDSX) in meat ducks and provide the foundation for further in-depth study of the pathogenic mechanism of this virus.

Fowl adenovirus serotype 4: Epidemiology, pathogenesis, diagnostic detection, and vaccine strategies

Fowl adenovirus (FAdV) serotype-4 is highly pathogenic for chickens, especially for broilers aged 3 to 5 wk, and it has emerged as one of the foremost causes of economic losses to the poultry industry in the last 30 years. The liver is a major target organ of FAdV-4 infections, and virus-infected chickens usually show symptoms of hydropericardium syndrome. The virus is very contagious, and it is spread both vertically and horizontally. It can be isolated from infected liver homogenates and detected by several laboratory diagnostic methods (including an agar gel immunodiffusion test, indirect immunofluorescence assays, counterimmunoelectrophoresis, enzyme-linked immunosorbent assays, restriction endonuclease analyses, polymerase chain reaction (PCR), real-time PCR, and high-resolution melting-curve analyses). Although inactivated vaccines have been deployed widely to control the disease, attenuated live vaccines and subunit vaccines also have been developed, and they are more attractive vaccine candidates. This article provides a comprehensive review of FAdV-4, including its epidemiology, pathogenesis, diagnostic detection, and vaccine strategies.

A subunit vaccine based on fiber-2 protein provides full protection against fowl adenovirus serotype 4 and induces quicker and stronger immune responses than an inactivated oil-emulsion vaccine

As the number of hepatitis hydropericardium syndrome (HHS) cases has increased in recent years in China, development of a safe and effective vaccine is now urgent. To address this problem a subunit vaccine is a good option, we here systematically investigated the minimum immune dose of a subunit vaccine against HHS based on recombinant fowl adenovirus serotype 4 (FAdV-4) fiber-2 protein and compared the effects between this subunit vaccine and an inactivated oil-emulsion FAdV-4 vaccine in a vaccination trial. The results revealed that the lowest dose of recombinant fiber-2 protein that could provide 100% protection against challenge with virulent FAdV-4 strain HB1501 as well as elicit protective immunity was 2.5 μg/bird. Neither clinical signs nor gross lesions were observed in chickens. In addition, immunization of specific-pathogen-free (SPF) chickens with recombinant fiber-2 protein (≥2.5 μg/bird) could induce quicker and stronger immune responses than the inactivated oil-emulsion FAdV-4 vaccine. These findings provide important information about the development of subunit vaccines for the control of HHS.

Molecular analysis of the hexon, penton base, and fiber-2 genes of Korean fowl adenovirus serotype 4 isolates from hydropericardium syndrome-affected chickens

Fowl adenovirus serotype 4 (FAdV-4) is the causative agent of hydropericardium syndrome (HPS), a highly pathogenic disease in poultry. In the present study, hexon, penton base, and fiber-2 genes encoding major capsid proteins were analyzed in four FAdV-4 isolates from HPS-affected chickens in Korea. Nucleotide sequences of the entire hexon (2811 bases), penton base (1578 bases), and fiber-2 (1425 bases) genes from the Korean isolates were 97.5-99.3, 99.1-99.7, and 95.5-99.0 % identical, respectively, to those of foreign FAdV-4 isolates. In the N-terminal tail region of fiber-2, the KRP motif predicted to be the nuclear localization signal was identified in the Korean isolates, whereas KRP/A was detected in other isolates. The VYPF motif in fiber-2, which is known to interact with the penton base, was present in the same region of all FAdV-4 isolates that were compared. Amino acid variations in fiber-2 for HPS and non-HPS isolates revealed that D219 and T300 were conserved among ten HPS isolates from five countries, including Korea. T380 in fiber-2, previously found in HPS isolates, corresponded to A380 in the Korean isolates, indicating that T380 is not relevant for increased virulence. Phylogenetic analysis showed that the four Korean FAdV-4 isolates were more related to MX-SHP95, a Mexican FAdV-4 isolate of HPS origin, than to FAdV-4 isolates of Indian and Chinese origin, suggesting that the genetic relationship among FAdV-4 isolates is independent of geographic distribution. The molecular features of these genes will provide valuable information for vaccine development against HPS in the future.

Adenovirus in Rural Côte D'Ivoire: High Diversity and Cross-Species Detection

The Taï region in Western Côte d'Ivoire is characterized by extensive overlap of human and animal habitats. This could influence patterns of adenovirus transmission between humans and domestic animals. Fecal samples from humans and various domestic animals were tested for the presence of adenoviruses by PCR. Phylogenetic and species delineation analyses were performed to further characterize the adenoviruses circulating in the region and to identify potential cross-species transmission events. Among domestic animals, adenovirus shedding was frequent (21.6% of domestic mammals and 41.5% of chickens) and the detected strains were highly diverse, several of them representing novel types. Although no evidence for zoonotic transmission of animal adenovirus was obtained, the present study provides concordant evidence in favor of common cross-species transmission of adenoviruses between different animal species and first indications for adenovirus transmission from humans to animals. These findings underline the thus far underestimated importance of reverse zoonotic transmission of viruses and of the role of domestic animals as pathogen reservoirs, "bridge species," or intermediate hosts.

Epidemiological investigation of outbreaks of fowl adenovirus infection in commercial chickens in Korea

In total, 39 clinical cases of fowl adenoviruses (FAdV) infection in chickens (28 broiler, 7 native, and 4 layer chickens) between 2007 and 2010 in Korea were investigated. The FAdV types 4, 8b, and 11 comprised 18, 9, and 12 clinical cases, respectively. All FAdV type 4 cases showed clinical hydropericardium (HPS) lesions as well as inclusion body hepatitis (IBH), whereas all FAdV types 8b and 11 cases exhibited IBH lesions without HPS. All 3 types were detected in broiler (9-30 d old) and layer chickens (23-112 d old), whereas most native chickens (14-65 d old) were affected only by FAdV type 4. Infectious bursal disease virus and chicken infectious anemia virus were complications in 51.3% of FAdV cases, with mortalities of 55% to <0.1%. Chicken infectious anemia virus was detected in all native chicken cases. These results indicate that preventive measures against FAdV infection and immunosuppressive diseases on poultry farms should be implemented.

Inclusion body hepatitis caused by fowl adenovirus in broiler chickens in Japan, 2009-2010

From January 2009 to June 2010, many broiler chicks suddenly died without clinical signs. The mortality rates were from 1.2% to 17.0% in affected flocks. Inclusion body hepatitis (IBH) was detected in 13 prefectures (northern, eastern, western, and southern areas) in Japan. The livers were enlarged and pale. The bursa of Fabricius and thymus had not atrophied. Multifocal necroses of hepatocytes with basophilic intranuclear inclusions were seen in the liver. Eosinophilic intranuclear inclusion bodies in hepatocytes were rare. Focal necrosis of acinar cells with basophilic intranuclear inclusions was found in the pancreas. Basophilic intranuclear inclusion bodies were detected in intact surface epithelial cells of gizzard and epithelial cells of the small intestine. The intranuclear inclusions of liver, pancreas, gizzard, and small intestine were stained positively for immunohistochemistry of fowl adenovirus (FAV) antigen. Ultrastructurally, basophilic intranuclear inclusions consisted of viral particles approximately 70 nm in diameter and arranged in a crystalline array. FAV was isolated from the liver of chickens affected with IBH. The serotype of most isolates was 2. This study suggests that IBH produced by FAV is epidemic in broiler chicks in Japan and that the present cases occurred as the primary disease without the association of infectious bursal disease virus or chicken anemia virus.