Complete genome sequence and pathogenicity of fowl adenovirus serotype 4 involved in hydropericardium syndrome in Southwest China

Immunoprotection of FliBc chimeric fiber2 fusion proteins targeting dendritic cells against Fowl adenovirus serotype 4 infection

Hepatitis-hydropericardium syndrome (HHS) is a highly fatal disease in chickens caused by the highly pathogenic fowl adenovirus serotype 4 (FAdV-4), which has severe economic consequences. The fiber2 protein exhibits excellent potential as a candidate for a subunit vaccination against FAdV-4. Despite having a high safety profile, subunit vaccines have low immunogenicity due to their lack of infectivity, which leads to low levels of immune response. As a vaccine adjuvant, Salmonella flagellin possesses the potential to augment the immunological response to vaccinations. Additionally, a crucial strategy for enhancing vaccine efficacy is efficient presentation of immune antigens to dendritic cells (DC) for targeted vaccination. In this study, we designed FAdV-4-fiber2 protein, and a recombinant protein called FliBc-fiber2-SP which based on FAdV-4-fiber2 protein, was generated using the gene sequence FliBc, which retains only the conserved sequence at the amino and carboxyl termini of the flagellin B subunit, and a short peptide SPHLHTSSPWER (SP), which targets chicken bone marrow-derived DC. They were separately administered via intramuscular injection to 14-day-old specific pathogen-free (SPF) chickens, and their immunogenicity was compared. At 21 d postvaccination (dpv), it was found that the FliBc-fiber2-SP recombinant protein elicited significantly higher levels of IgG antibodies and conferred a vaccine protection rate of up to 100% compared to its counterpart fiber2 protein. These results suggest that the DC-targeted peptide fusion strategy for flagellin chimeric antigen construction can effectively enhance the immune protective efficacy of antigen proteins.

Genetic modification regulates pathogenicity of a fowl adenovirus 4 strain after cell line adaptation (genetic mutation in FAdV-4 lowered pathogenicity)

Fowl adenovirus 4 (FAdV-4) is a major avian virus that induces fatal diseases in chicken such as, hydropericardium and hepatitis. The viral structure consists of hexon, penton, fiber-1, and fiber-2 which are associated with immunopathogenesis. In this study, we investigated the genetic modification of a FAdV-4 strain after continuous passages in a cell line and evaluated the pathogenicity associated with mutations. We used the FadV-4 KNU14061 strain, which was isolated from layers in 2014. The virus went through 80 passages in the Leghorn male hepatoma (LMH) cell line. The full genetic sequence was identified, and we found a frameshift in the fiber-2 amino acid sequence after the initial thirty passages. To examine whether the frameshift in the fiber-2 gene affects the pathogenicity in chicken, we inoculated LMH80 (80 times passaged) and LMH10 (10 times passaged) into 3-day-old chickens and examined the pathogenesis. LMH10 infection via intramuscular route induced fatal pathology, but LMH80 did not. Furthermore, LHM80 pre-treatment protected hosts from the LMH10 challenge. Thus, the genetic modification isolated by serial passage lowered pathogenicity and the resulting virus acted as an attenuated vaccine that can be a FAdV-4 vaccine strain candidate.

Pathogenicity and epidemiological survey of fowl adenovirus in Shandong Province from 2021 to 2022

In recent years, the poultry industry had been markedly affected by adenoviral diseases such as hydropericardium syndrome and inclusion body hepatitis caused by fowl adenovirus (FAdV), which have become increasingly prevalent in China. Shandong Province, China, is an important area for poultry breeding where various complex and diverse FAdV serotypes were isolated. However, the dominant strains and their pathogenic characteristics are not yet reported. Therefore, a pathogenicity and epidemiological survey of FAdV was conducted, showing that the local dominant serotypes of FAdV epidemics were FAdV-2, FAdV-4, FAdV-8b, and FAdV-11. Their mortality rates in the 17-day-old specific-pathogen-free (SPF) chicks ranged from 10 to 80%; clinical signs included mental depression, diarrhea, and wasting. The maximum duration of viral shedding was 14 days. The highest incidence in all infected groups was on days 5-9, and then gradual regression occurred thereafter. The most pronounced symptoms occurred in chicks infected with FAdV-4, including pericardial effusion and inclusion body hepatitis lesions. Our results add to the current epidemiological data on FAdV in poultry flocks in Shandong and elucidate the pathogenicity of dominant serotypes. This information may be important for FAdV vaccine development and comprehensive epidemic prevention and control.

Complete genome sequence and pathogenicity analysis of a highly pathogenic FAdV-4 strain

Fowl adenovirus serotype 4 (FAdV-4) is a double-stranded DNA virus that mainly infects broiler chickens and has caused huge economic losses to the poultry industry. Recently, an FAdV-4 strain, SDLC202009, the causative pathogen of hydropericardium-hepatitis syndrome (HHS) in Liaocheng, Shandong, was isolated from commercial laying hens and propagated in specific pathogen free SPF chicken embryos. Pathogenicity studies showed that SDLC202009 could infect SPF chicken embryos and chickens, with a mortality rate of 100%. The complete genome was sequenced, and phylogenetic analysis showed that SDLC202009 belonged to the FAdV-4 cluster, with a genome length of 43, 077 bp. The SDLC202009 had 99.9% identity with the JSJ13 and SD1601, which were recently isolated in China. Compared to the recently isolated strain in China, SDLC202009 had deleted open reading frame 19 (ORF19), ORF27, ORF48, and ORF0. SDLC202009 harbored amino acid site mutations in the main structural proteins hexon, fiber1, and fiber2 similar with those in highly pathogenic strains. Furthermore, SDLC202009 showed unique mutations in hexon A571P, fiber1 E216K, and fiber2 N98K. In summary, our findings provide theoretical support for prevention and control of the HHS.

Detection, Quantification and Molecular Characterization of Fowl Adenoviruses Circulating in Ecuadorian Chicken Flocks during 2019-2021

Fowl adenoviruses are a group of pathogens that cause large economic losses worldwide in the poultry industry, in addition to producing a wide range of diseases, such as IBH, HHS, and enteric and respiratory diseases. The objective of this study was to quantify, identify, and molecularly characterize the types of FAdV circulating in commercial poultry farms (broilers, breeders, and layers) in Ecuador from 2019 to 2021. Molecular characterization was performed by PCR, quantification by qPCR, and subsequent sequencing for each positive sample. The results indicated that the FAdV genotypes circulating in our country are FAdV-2/D2, FAdV-6/E1, FAdV-8a/E2, and FAdV-11/D3; the samples were grouped into different groups that contain sequences that were obtained from countries in Africa, Asia, and America, and that are found in birds at different ages, since early age where can cause different clinical signs, such as diarrhea, ruffled feathers and dwarfism. Therefore, these results indicate that several genotypes of the virus are circulating in commercial poultry flocks, suggesting that biosecurity measures on farms should be improved, in addition to carrying out new or improved vaccination plans.

Chicken interferon-induced transmembrane protein 1 promotes replication of coronavirus infectious bronchitis virus in a cell-specific manner

Interferon-induced transmembrane proteins (IFITMs) are broad-spectrum antiviral proteins that inhibit numerous virus infections by impeding viral entry into target cells. However, increasing evidence suggests diverse functions of IFITMs in virus infection, especially with the coronavirus. We analyzed the effect of chicken interferon-induced transmembrane proteins (chIFITMs) on coronavirus infectious bronchitis virus (IBV) infection in vitro. We demonstrated that the antiviral effects of IFITMs are dependent on cell and virus types. The overexpression of chIFITM1 dramatically promoted the replication of IBV Beaudette strain in the chicken hepatocellular carcinoma cell line, LMH. Mechanistically, chIFITMs share roughly the same subcellular localization in different host cells, and overexpressed of chIFITM1 have no effect of viral attachment and entry. Further studies revealed that mutations of amino acids at key positions (60KSRD63, 68KDFV71) in the intracellular loop domain (CIL) caused loss of the promoted function. Interaction with downstream proteins in co-response to viral infection could be the primary reason behind variable functions of chIFITM1 in different cells. In all, our study explored the functions of chIFITMs in viral infection from a new perspective.

Epidemiological survey of avian adenovirus in China from 2015 to 2021 and the genetic variability of highly pathogenic Fadv-4 isolates

The prevalence of poultry adenovirus in China is determined using clinical diagnosis, molecular biological testing, serological testing, and LMH cell virus isolation. These methods can track and test key poultry and waterfowl breeding areas across the country. From 2015 to 2021, 9613 suspected adenovirus samples were collected from 28 provinces. After the first generation of gene sequencing, a total of 2210 hexo gene fragments were obtained. Among them, FAdV-1 type accounted for 7.65%, FAdV-2 type accounted for 5.34%, FAdV-3 type accounted for 2.04%, FAdV-4 type accounted for 38.24%, FAdV-5 type accounted for 2.17%, FAdV-6 type accounted for 0.32%, FAdV-7 type accounted for 0.77%, FAdV-8a type accounted for 10.63%, FAdV-8b type accounted for 11.58%, FAdV-9 type accounted for 0.50%, FAdV-10 type accounted for 8.10%, and FAdV-11 type accounted for 12.67%. A total of 877 FAdV strains were isolated from FAdV suspected samples by seeding LMH cells, and there were 475 FAdV-4 strains among them. A total of 473 isolates were highly pathogenic FAdV-4, and the percentage of amino acid homology with the highly pathogenic FAdV-4 reference strains was >99.1%. Two isolates were non-pathogenic, and the amino acid homology with the ON1 reference strain was >99.6%. Part of the amino acid positions of the hexon gene have mutations, including positions 188, 193, 195, 238, and 240.

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.

Pathogenicity and virus shedding ability of fowl adenovirus serotype 4 to ducks

Fowl adenovirus serotype 4 (FAdV-4) is the pathogen causing hepatitis-hydropericardium syndrome (HHS) in broilers. Since June 2015, it has emerged as one of the leading causes of economic losses in the poultry industry in China. Although most studies on FAdV-4 have focused on its pathogenicity to broilers, limited studies have been performed on other natural hosts such as ducks and geese. In this study, we assessed the pathogenicity of FAdV-4 to ducks of different ages through intramuscular injection and found that infected ducks showed severe growth depression. The infected ducks also suffered from extensive organ damage and had histopathological changes in the liver, spleen, and kidney. Although the virus infection caused lymphocyte necrosis of immune organs and the development of the bursa of Fabricius (bursa) was inhibited, the humoral immune response of infected ducks to FAdV-4 remained strong. The infected ducks also had high viral load in tissues and shed virus after the challenge. Overall, our research demonstrates that FAdV-4 can infect ducks and adversely affect the productivity of animals. And the viruses shed by infected ducks can pose a potential risk to the same or other poultry flocks.

The fowl adenovirus serotype 4 (FAdV-4) induce cellular pathway in chickens to produce interferon and antigen-presented molecules (MHCI/II)

FAdV-4 is the major strain of adenovirus that responsible for hydro-pericardial syndrome (HPS) in poultry. In this study, the virus's specific gene fragments were isolated from clinically suspected cases and amplified by PCR. Finally, after a viral infection to investigate the immune response of the host, the gene expression of MHC (major histo-compatible) molecules (MHCIα, MHCIIβ), Ii (Invariant Chain) gene, inflammatory cytokines (IFN-β, IFN-γ, and IL-1β), and transcription factors (MDA5, STING, IRF7, and NF-kB) were detected by real-time PCR (fluorescence technology). The results of sequence comparison showed that the clinically isolated virus was 100% homologous to a virulent strain of avian adenovirus group C serotype 4 (FAdV-4), which were named AH-FAdV-4. The TCID₅₀ and pathogenicity of the virus were determined that was 10^6.52/0.1 mL with a mortality rate of 100% in chickens and 0% in ducks. Furthermore, results showed that the expression level of MHCIα, MHCIIβ, and Ii genes in chicken embryo kidney cells significantly (P < 0.01) upregulated (increased) after infection, which was 43, 5.2, and 2.5 times higher than the control group. With the addition of PDTC, an inhibitor of NF-kB, then the expression level of MHCIα, MHCIIβ, and Ii was decreased significantly (P < 0.01) than the control group. The transcription levels of these genes were decreased 0.64, 0.27, and 0.26 respectively. Simultaneously, the expression levels of IFN-β, IFN-γ, and IL-1β were also significantly (P < 0.01) up-regulated (increased) 7.8, 22.7, and 5 times higher than the control group. It was found that up-regulation of STING and NF-κB pathways are directly involved in the regulation of inflammatory cytokines (IFN-β, IFN-γ, and IL-1β), MHC molecules (MHCIα, MHCIIβ), and Ii gene. The results also showed that the gene regulation pathways consecutively increased the expression levels of MDA5, STING, IRF7, and NF-kB. It is conducted that the expression levels of cytokines, MHC molecules, and li gene were increased by STING and NF-kB pathways.

Pathogenicity and Immune Responses in Specific-Pathogen-Free Chickens During Fowl Adenovirus Serotype 4 Infection

Hydropericardium-hepatitis syndrome, a recently emerged disease of chickens, is caused by some strains of fowl adenovirus serotype 4 (FAdV-4). However, the relationship between the immune response and cytokine expression during FAdV-4 infection is largely unknown. In this study, our data showed that all chickens exhibited typical clinical signs and lesions and that the viral load was significantly increased in both the liver and thymus following FAdV-4 infection. We also found that the appearance of tissue lesions in the liver and thymus was consistent with the viral copy numbers, indicating that virus replication in systemic organs closely correlated with disease progression. In addition, the effects of FAdV-4 infection on the transcription of some avian cytokines were studied in vivo. In general, expression of the proinflammatory cytokines interleukin (IL)-2 and interferon (IFN)-α and IFN-β in the liver and thymus was strongly upregulated. Interestingly, the expression of IL-2 was the most highly upregulated. Expression of the anti-inflammatory cytokines IL-4, IL-10, and transforming growth factor (TGF)-β1 and TGF-β2, were also upregulated. Moreover, we investigated both the humoral and cellular immune responses in chickens infected with FAdV-4. Compared to those in the noninfected chickens, the antibody levels in chickens infected with FAdV-4 were significantly increased within 30 days postinfection. In addition, the ratio of CD4+/CD8+ T cells was decreased in FAdV-4-infected chickens. Taken together, these findings increase our understanding of the pathogenesis of FAdV-4 in chickens and provide a foundation for additional pathogenesis studies.

Molecular characterization and pathogenicity of a fowl adenovirus serotype 4 isolated from peacocks associated with hydropericardium hepatitis syndrome

In September 2019, a highly prevalent infectious disease caused severe hydropericardium hepatitis syndrome (HHS) in a peacock farm in Central China. The disease showed high mortality of 78.6% in 28-42 day-old peacocks. In this study, one strain of highly pathogenic fowl adenovirus serotype 4 (FAdV-4) was isolated from peacocks and designated as HN19. Molecular characterization of amino acid revealed that HN19 contains the same deletions as the dominate strains in chickens in China recently. Phylogenetic analyses revealed that HN19 showed higher homology with other FAdV-4 strains isolated from China, indicating that HN19 might originate from previously FAdV-4 predecessor in China. Experimental infection of the HN19 strain via intramuscular injection led to 100% mortality rate in 21-day-old specific pathogenic-free (SPF) chickens. To our knowledge, this represents the first report on the prevalence of FAdV-4 in peacocks. These results suggested that the potential risk of cross-species transmission of FAdV-4 from chickens to peacocks, highlighting the need for implementing strict biosecurity measures to avoid the mixing of different bird species.

Genetic Characterization and Pathogenicity Analysis of Recently Isolated Fowl Adenovirus 8b in Korea

A Korean field strain of fowl adenovirus (FAdV) 8b was isolated from chickens showing high mortality. Isolated FAdV-8b strains with the hexon and fiber genes were genetically analyzed. The Korean FAdV-8b (K194/19) strain isolated in 2019 showed higher sequence identity with the FAdV-8b strain isolated in China but lower sequence identity with the Korean FAdV-8b (K187/08) strain isolated in 2008. The K194/19 strain formed a distinct subcluster within the FAdV-8b cluster in a phylogenetic tree based on hexon and fiber genes. FAdV can infect day-old chicks through vertical transmission, and so blood samples were obtained from 54-, 60-, and 63-wk-old parent chickens. FAdV-specific antibody levels were investigated with ELISA and virus neutralization (VN) tests with the K194/19 and K187/08 strains as antigens. In VN tests, all sera neutralized the K187/08 strain. However, the K194/19 strain was neutralized by sera collected from 60- and 63-wk-old chickens but not sera obtained from 54-wk-old chickens, indicating natural infection. Finally, to determine the pathogenicity of the K194/19 strain, 1-day-old and 4-wk-old specific-pathogen-free birds were infected with the K194/19 and K187/08 strains. No significant difference in pathogenicity was observed between the two strains. Although the K194/19 strain showed similar pathogenicity with the K187/08 strain, differences in nucleotide and amino acid sequences of the hexon and fiber genes may determine the evasion ability of the K187/08 neutralizing antibody, indicating the need for development of a novel FAdV vaccine.

Pathogenicity and Molecular Typing of Fowl Adenovirus-Associated With Hepatitis/Hydropericardium Syndrome in Central China (2015-2018)

In central China, a large number of broiler and layer flocks have suffered from outbreaks of severe hepatitis/hydropericardium syndrome (HHS). This resulted in huge economic losses to the poultry industry, from 2015 to 2018. To identify the specific pathogen and study its pathogenicity, 195 samples from Hubei, Jiangxi, Anhui, Hunan, and Henan provinces in central China were collected. The samples were screened for the adenovirus hexon gene, and neighbor joining was used for the phylogenetic reconstruction of the sequences. Among the collected samples, 122 were found to be positive for fowl adenovirus (FAdV) by PCR, and 73 isolates were obtained. The predominant viral serotype was serotype 4 (FAdV-4), which was found in 48 isolates, while 24 were serotype 10 (FAdV-10), and one was serotype 2 (FAdV-2). The CH/HBTF /1710 isolate was selected for further experiment and inoculated into 33-day-old specific pathogen-free chickens via intramuscular injection or oral administration to evaluate pathogenicity. It was found that the mortality for chickens infected by intramuscular injection or oral administration was 70 and 60%, respectively. Necropsy revealed mild to severe hepatitis and hydropericardium at 5 and 7 days after infection. Ancestor analyses indicated that all of the FAdV-4 strains obtained in this study shared a common Indian precursor and had a close genetic relationship with the JSJ13, SDSX, HN/151025, and SDDM-15 strains common in China.

Fowl Adenovirus (FAdV) Recombination with Intertypic Crossovers in Genomes of FAdV-D and FAdV-E, Displaying Hybrid Serological Phenotypes

After analyzing 27 new genomes from fowl adenovirus (FAdV) field isolates and so-far unsequenced prototypes, we report the first evidence for recombination in FAdVs. Recombination was confined to species FAdV-D and FAdV-E, accommodating the largest number of, and the intraspecies-wise most differentiated, types. The majority of detected events occurred in FAdV-E, involving segments with parental origin of all constitutive types. Together with the diversity of breakpoints, this suggests widespread recombination in this species. With possible constraints through species-specific genes and diversification patterns, the recombinogenic potential of FAdVs attains particular interest for inclusion body hepatitis (IBH), an important disease in chickens, caused by types from the recombination-prone species. Autonomously evolving, recombinant segments were associated with major sites under positive selection, among them the capsid protein hexon and fiber genes, the right-terminal ORFs 19, 25, and the ORF20/20A family. The observed mosaicism in genes indicated as targets of adaptive pressures points toward an immune evasion strategy. Intertypic hexon/fiber-recombinants demonstrated hybrid neutralization profiles, retrospectively explaining reported controversies on reference strains B3-A, T8-A, and X11-A. Furthermore, cross-neutralization supported sequence-based evidence for interdomain recombination in fiber and contributed to a tentatively new type. Overall, our findings challenge the purported uniformity of types responsible for IBH, urging more complete identification strategies for FAdVs. Finally, important consequences arise for in vivo studies investigating cross-protection against IBH.

Characterization of fowl adenovirus serotype 4 circulating in chickens in China

Outbreaks of fowl adenovirus (FAdV) has resulted in huge economic losses in poultry industry in China since 2015. This study detected the pathogens from diseased chickens and determined that fowl adenovirus serotype 4 (FAdV-4) and co-infection of immunosuppressive pathogens were the causes of the outbreaks. Phylogenetic analysis results indicated that these pandemic strains originated from previously FAdV-4 predecessor in China and had obtain gene mutations that might contribute to enhanced pathogenicity of these strains. Compared with early strains, the pathogenicity of novel FAdV-4 strains significantly increased, which led to systemic infections and injuries to multiple organs in the infected chickens. Our study could provide useful information for understanding of the FAdV-4 and favorable theory basis for clinical prevention and control of the disease.

Pathogenicity of a fowl adenovirus serotype 4 isolated from chickens associated with hydropericardium-hepatitis syndrome in China

Hydropericardium-hepatitis syndrome (HHS) is characterized by pericardial effusion and hepatitis and causes huge economic losses in the poultry industry in China. In this study, a strain of fowl adenoviruses (FAdV-4) (GX-1) was isolated from liver samples of diseased chickens with HHS. Phylogenetic analysis based on complete genome gene revealed that GX-1 clustered with the C-type fowl adenovirus and was serotyped as FAdV-4. Pathogenicity testing showed that the GX-1 strain caused 100% mortality in 10-day-old specific pathogen-free chickens at a dose of 104 tissue culture infective doses (TCID50) within 3 d post-infection. A viral dose of 103 TCID50 resulted in a 16% survival rate before day 9 and at 102 TCID50 an 80% rate before day 6. At necropsy, livers from infected chickens were swollen and yellow brown with necrotic foci. The hearts were flabby with amber-colored and jelly-like fluid in the pericardial sacs. The kidneys were swollen and congested. Histologically eosinophilic intranuclear inclusion body could be seen in the hepatic cell. The result of histopathological examination also revealed that heart muscle fibers were fractured with extensive congestion and hemorrhaging. Other tissues like kidney, bursa of Fabricius, thymus, and spleen were observed degeneration and necrosis. Virus-specific antibodies appeared in serum beginning at day 14 and reached statistically significant levels at 21, 28, 35, and 42 dpi (P < 0.001). In conclusion, we identified a highly virulent FAdV-4 virus as causative agent of the HHS outbreak reported here. The FAdV-4 GX-1 strain will be valuable for vaccine evaluation and development to prevent and reduce the spread of HHS in the poultry industry.

Pathogenicity of fowl adenovirus (FAdV) serotype 4 strain SDJN in Taizhou geese

Hydropericardium hepatitis syndrome (HHS) is a fatal disease in chickens, mainly caused by fowl adenovirus serotype 4 (FAdV-4). Since June 2015, HHS has appeared in many provinces in China. The disease has spread from broilers to laying hens, breeders and Cherry Valley ducks, seriously endangering the health of the poultry industry in China. In July 2016, an infectious disease was noticed in a goose farm in Jinan, Shandong Province, China, and hydropericardium was the main finding in post mortem investigations. In the actual study, we isolated a FAdV-4 strain from the livers of naturally-infected goslings and designated it as SDJN. We first evaluated its pathogenicity by inoculating Taizhou geese at 10, 20, and 30 days of age with 10^-7.15EID₅₀/0.2 ml doses of the SDJN strain in 1 ml allantoic fluid via subcutaneous injection or oral infection. Clinical signs and pericardial effusion appeared in geese infected subcutaneously at 10 days of age, whereas 20- and 30-day-old geese were not susceptible to FAdV-4. The results of real-time PCR showed that the replication ability of FAdV-4 in geese correlated with the age. Furthermore, results from clinical chemistry showed that FAdV-4 damaged the liver and kidney in geese and the results paralleled viral load and gross lesions. Consequently, FAdV-4 was pathogenic in geese, and the pathogenicity was related to age and mode of infection. This study is the first experimental infection of FAdV-4 in geese, which will provide a basis for further understanding of the disease. RESEARCH HIGHLIGHTS Pathogenicity tests with a FAdV-4 were conducted in geese, which included data on clinical signs, gross pathology, histopathology, clinical chemistry and viral load. FAdV-4 could replicate in geese and HHS was successfully induced. Pathogenicity of FAdV-4 in geese was related to the age and routes of infection.

LAMP real-time turbidity detection for fowl adenovirus

Background

Fowl adenovirus (FAdV) is an infectious agent that can cause jaundice, severe anaemia, dyspnoea and reproductive disorders in fowls. Since 2015, FAdV disease has been rapidly spreading among broiler chickens in China, where it has caused significant economic losses. In this study, a loop-mediated isothermal amplification (LAMP) real-time turbidity method with strong specificity to FAdV was established.

Results

The established assay was specific to FAdV-4, and the lower limit of detection was 75 copies/μL of extracted DNA. The positive detection rate for the suspected tissue samples was 33.3% (14/42), which was consistent with that of the real-time PCR.

Conclusion

The proposed LAMP method can quickly and accurately detect prevalent FAdV via real-time turbidity assay, thereby providing a diagnostic platform for the prevention and control of the FAdV disease.

Identification, Pathogenicity of Novel Fowl Adenovirus Serotype 4 SDJN0105 in Shandong, China and Immunoprotective Evaluation of the Newly Developed Inactivated Oil-emulsion FAdV-4 Vaccine

Since mid-2015, numerous outbreaks of hydropericardium-hepatitis syndrome (HHS), which is caused by a novel fowl adenovirus serotype 4 (FAdV-4), have been reported in chickens in parts of China, thereby causing huge economic losses to the poultry industry. Thus, an effective vaccine to control the further spread of infections with this hyper-virulent FAdV-4 is imperative. In this study, we isolated a novel FAdV-4 strain SDJN0105 from a broiler farm with HHS disease in Shandong Province. Pathogenicity was evaluated by the observation of clinical symptoms, necropsy changes, and pathological tissue sections after oral and intramuscular (IM) infection of Specific pathogen free (SPF) chickens. The chickens infected by IM injection all died within three days, and chickens infected via the oculonasal route died within five days post-infection (dpi). Histopathological examination revealed that the pathology was confined to heart, liver, spleen, lung, kidney, and particularly the liver. Irrespective of the inoculation route, the highest viral DNA copy numbers were detected in the livers of infected chickens. The mRNA expression levels of IL-1β, IL-6, IL-8, IFNs, TNF-α, Mx, and OASL were significantly upregulated during the viral infection. In addition, an inactivated oil-emulsion FAdV-4 vaccine was developed. The vaccine could provide full protection for SPF chickens against a lethal dose of the FAdV-4 strain SDJN0105 and a high level of antibodies. These results improve our understanding of the innate immune responses in chickens infected with FAdV-4 and the pathogenesis of FAdV-4 caused by host factors, and the developed FAdV-4 vaccine is promising as a drug candidate for the prevention and reduction of the spread of HHS in poultry in China.

Transcriptome analysis of fowl adenovirus serotype 4 infection in chickens

Fowl adenovirus serotype 4 (FAdV-4) is a causative agent of inclusion body hepatitis and hydropericardium–hepatitis syndrome. These diseases cause considerable economic losses in the global poultry industry and are significant stressors for infected chickens. However, the molecular mechanisms of FAdV-4 pathogenesis are poorly understood. In the present study, we identified differentially expressed genes from the livers of FAdV-4-infected chickens using RNA-seq at 7, 14 and 21 days after FAdV-4 infection. We identified 2395 differentially expressed genes at the three time points. These genes were enriched in variety of biological processes and pathways including PPAR and Notch signaling, cytokine–cytokine receptor interactions and Toll-like receptor signaling pathways. The transcriptional data were validated by quantitative real-time PCR. Our results will assist in the understanding of the molecular pathogenesis of FAdV-4 infection and for developing novel antiviral therapies.

Genetic characterization of fowl adenovirus serotype 4 isolates in Southern China reveals potential cross-species transmission

Increasing numbers of hepatitis-hydropericardium syndrome (HHS) outbreaks associated with Fowl adenovirus 4 (FAdV-4) have been confirmed in several provinces of China since 2015, mainly affecting 3-5-week-old broiler chicks, resulting in significant losses to the poultry industry. However, little is currently known regarding the molecular epidemiology and host specificity of FAdV-4 associated with HHS in Southern China. In the present study, we isolated 37 FAdV-4 strains from 52 suspected cases of HHS (33 from broilers, one from a layer, two from ducks, and one from a mandarin duck) from Guangdong province during 2016 to 2017. All 37 FAdV-4 strains obtained showed 100% identity of hexon genes at the nucleotide level, and also showed 100% nucleotide sequence identities with strains obtained from other provinces such as Shandong, Zhejiang, and Anhui, which grouped into a FAdV-C cluster. To our knowledge, this represents the first report of an FAdV-4 strain (GZ1) from a mandarin duck with HHS. Experimental infection of the GZ1 strain via intramuscular injection led to a 100% mortality rate in 21-day-old specific pathogen-free chickens. These data indicate the possibility of the cross-species transmission of FAdV-4, highlighting the need for implementing strict biosecurity measures to avoid the mixing of different bird species.

Prevalence of Fowl Adenovirus Serotype 4 and Co-Infection by Immunosuppressive Viruses in Fowl with Hydropericardium Hepatitis Syndrome in Shandong Province, China

Fowl adenovirus serotype 4 (FAdV-4) is the pathogenic agent of hydropericardium hepatitis syndrome (HHS) in chickens and ducks, which has caused huge economic losses for the Chinese poultry industry since 2015. In order to objectively determine the prevalence and co-infection status of the virus in Shandong province in China, we analyzed a total of 679 clinical cases of chickens and ducks from 36 farms in the province. The results showed that the FAdV-4 infection rate was 65.2% (443/679), and the rate in breeder ducks was almost two-fold higher than that in breeder chickens (68.57% vs. 34.30%). Notably, co-infection by H9N2 avian influenza virus, infectious bursal disease virus, and/or chicken infectious anemia virus was very common in the 443 FAdV-4-positive cases. Furthermore, phylogenetic analysis of the hexon genes of four Shandong FAdV-4 isolates revealed that these strains clustered into Indian reference strains, indicating that the Shandong FAdV-4 strains might have originated in India. These findings provide the first data on the prevalence and co-infection status of FAdV-4 in Shandong province, which may serve as a foundation for the prevention of FAdV-4 in the field.

A loop-mediated isothermal amplification coupling with a lateral flow dipstick for rapid and specific detection of fowl adenovirus serotype-4

Fowl adenovirus serotype-4 (FAdV-4) has been recognized as a predominant threat to the broilers aged from three to five weeks. Hydropericardium syndrome (HPS) is one of its major clinical diseases by FAdV-4 resulting in heavy economic losses. In this study, a loop-mediated isothermal amplification coupling with a lateral flow dipstick (LAMP-LFD) was developed for rapid and specific detection of fowl adenovirus serotype-4. The optimized LAMP-LFD can be completed in 60 min at 65 °C. The minimum detection limits of PCR, real-time PCR, nested PCR and LAMP-LFD are 1 × 10⁴ copies/μl, 1 × 10² copies/μl, 10 copies/μl and 10 copies/μl respectively. Moreover, the specificity of the LAMP-LFD assay is satisfactory and does not produce cross reactions with other species. In field samples, 150 samples were assayed by PCR and LAMP-LFD. They agreed on the diagnosis "positive" in 13% of clinical samples, and they agreed on the diagnosis "negative" in 85% of clinical samples. Their probability of agreement is p₀ = 147/150 = 13% + 85% = 98%. LAMP-LFD can potentially be modified and applied as a diagnostic tool for FAdV-4 infection especially in resource-limited areas, such as small breeding farms and basic veterinary labs to offer an affordable diagnostic.

Airborne Transmission of a Serotype 4 Fowl Adenovirus in Chickens

Serotype 4 fowl adenovirus (FAdV-4) is the main pathogen for hydropericardium syndrome (HPS) in chickens. It has caused major economic losses in the global poultry industry. Currently, FAdV-4's transmission routes in chickens remain unclear. Here we investigate the airborne transmission routes of FAdV-4 in chickens. A total of 45 ten-day-old chickens were equally divided into three groups (infected group/isolator A, airborne group/isolator B, and control group/isolator C). Of note, isolators A and B were connected by a leak-free pipe. The results showed that the virus could form a viral aerosol, detected in isolators two days post infection (dpi). The viral aerosol reached a peak at 4 dpi in the infected group. Healthy chickens in the airborne group were infected by the virus at 8 dpi. The chickens of the airborne group demonstrated subclinical symptoms capable of shedding the virus for some time. This finding suggests that FAdV-4 can be efficiently transmitted among chickens by aerosol transmission. These findings have significant implications for developing strategies to control this infectious disease epidemic.

Development of a TaqMan-based real-time PCR for detecting duck adenovirus 3

Recently, a novel duck adenovirus (designated as duck adenovirus 3, DAdV-3) was discovered in Muscovy ducks, China. Here, we developed a TaqMan-based real-time PCR assay (qPCR) for the detection of DAdV-3 infection. After the optimization of the qPCR conditions, the lower limit of detection for DAdV-3 infection was 40.9 copies/μl. No cross-reactivity was observed with other duck-derived pathogens. Intra- and inter-assay variability was less than 2.30%. DAdV-3 was detected in embryos and newly hatched ducklings by qPCR assay, the findings provided evidence of possible vertical transmission of DAdV-3. The developed qPCR analysis showed high specificity, sensitivity, and reproducibility, thereby indicating that it can be used in future investigations on the pathogenesis and epidemiology of DAdV-3.