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

Generation of an artificially attenuated fowl adenovirus 4 viral vector using the reverse genetics system based on full-length infectious clone

Fowl adenovirus serotype 4 (FAdV-4) is a non-enveloped double-stranded DNA virus with a 43-45 kb genome. This characteristic makes it a promising viral vector for expressing other antigens in developing multi-valent or multi-series vaccines in the poultry industry. To create an easy-to-use reverse genetics system for manipulating FAdV-4 genomic DNA, a full-length infectious clone of FAdV-4 was constructed using lambda Red-mediated recombination in Escherichia coli DH10B. Viable viruses were successfully rescued after the transfection of linearised infectious clones into LMH cells. The rescued viruses showed the same cytopathic effect and growth kinetics as wild-type FAdV-4 viruses. Based on the FAdV-4 infectious clone, the hexon coding sequence of the high-pathogenicity FAdV-4 was replaced by that of the nonpathogenic FAdV-4 using lambda Red-mediated recombination combined with rpsL counter selection without leaving extra sequences after engineering. The rescued recombinant virus was highly attenuated and showed low pathogenicity to 21-day-old SPF chickens. Hereto, the easy-to-use reverse genetics system for FAdV-4 was successfully established. With this platform, the genomic DNA of FAdV-4 can be manipulated and purified in DH10B, making it quicker and easier to generate a recombinant FAdV-4 virus to develop multi-valent/multi-series vaccines.

Vaccination strategies to protect chickens from fowl adenovirus (FAdV)-induced diseases: A comprehensive review

In recent years, fowl adenovirus (FAdV)-induced diseases became a global problem with considerable impact on chicken health and welfare. This has prompted numerous studies to focus on experimental immunization strategies using whole virus formulations (live or killed vaccines), some of them modified as recombinantly constructed vector vaccines. In addition, FAdV capsid proteins were frequently reported as immunizing antigens (subunit vaccines), with fiber proteins being amongst the most successful candidates. To date, there is no standardized protocol to assess vaccine efficacy in experimental FAdV protection studies, with the consequence that the experimental settings present several degrees of variations even when sharing similar premises. Differences in formulation preparations, route of inoculation, antigen dose, vaccination scheme, choice of challenge strain, or type and age of the birds are capable to greatly influence the magnitude of the immune response and the consequent protective efficacy, altogether addressing remaining challenges. Beyond the antigen composition of a vaccine, the epidemiology of FAdVs with the potential of vertical transmission of virus and/or antibodies from breeders to progenies has a substantial impact on protection strategies. The goal of this review is to outline a broad overview of the findings made thus far regarding immunization strategies against diseases associated to FAdV infections, considering the literature published since the appearance of hepatitis-hydropericardium syndrome (HHS) in the late Eighties, in order to emphasize the current knowledge on FAdV vaccines and highlight fields of future research and intervention.

Comparative analysis of changes in immune cell in the chicken spleen across different ages using flow cytometry

BACKGROUND

Concurrent emerging and reemerging avian infectious diseases cause multiple risk factors in poultry. A body amount studies attempted to understand pathogen-associated immunity in chickens. Recent research has made progress in identifying immune functions in chicken, there are still gaps in knowledge, especially regarding immune responses during infectious diseases. A deeper understanding in chicken immune system is critical for improving disease control strategies and vaccine development.

RESULTS

This study proposes analytical method for chicken splenocytes, enabling the tracking changes in T cells, monocytes, and B cells across three ages. Optimized lymphocyte-activating conditions were suggested using concanavalin A and chicken interleikin-2, which facilitate immune cell activation and proliferation. Next, splenocytes from embryonic day 18, day 5, and day 30 were compared using surface markers and flow cytometry analysis. We observed an increase in T cell subsets, including activated T cells (CD4+CD44+ and CD8+CD44+), and B cells, along with a reduced monocyte population after hatching. However, morphological changes and genetic expression of functional immune molecules were limited.

CONCLUSIONS

The present findings on chicken immune system development offer valuable insights into the avian immune system, including analytical methods and the phenotypic and functional changes in immune cells. Updated immune-boosting strategies during the early stages of life are crucial for developing preventive measures against major infectious diseases in the poultry industry.

Pathogenicity of Duck Adenovirus Type 3 in Chickens

Duck adenovirus Type 3 (DAdV-3) severely affects the health of ducks; however, its pathogenicity in chickens remains unknown. The objectives of this study were to evaluate the pathogenicity and major pathological changes caused by DAdV-3 in chickens. Viral DNA was extracted from the liver of the Muscovy duck, and the fiber-2 and hexon fragments of DAdV-3 were amplified through polymerase chain reaction (PCR). The evolutionary tree revealed that the isolated virus belonged to DAdV-3, and it was named HE-AN-2022. The mortality rate of chicks that received inoculation with DAdV-3 subcutaneously via the neck was 100%, while the mortality rate for eye-nose drop inoculation was correlated with the numbers of infection, with 26.7% of chicks dying as a result of exposure to multiple infections. The main symptoms exhibited prior to death were hepatitis-hydropericardium syndrome (HHS), ulceration of the glandular stomach, and a swollen bursa with petechial hemorrhages. A histopathological examination revealed swelling, necrosis, lymphocyte infiltration, and basophilic inclusion bodies in multiple organs. Meanwhile, the results of quantitative real-time PCR (qPCR) demonstrated that DAdV-3 could affect most of the organs in chickens, with the gizzard, glandular stomach, bursa, spleen, and liver being the most susceptible to infection. The surviving chicks had extremely high antibody levels. After the chickens were infected with DAdV-3 derived from Muscovy ducks, no amino acid mutation was observed in the major mutation regions of the virus, which were ORF19B, ORF66, and ORF67. On the basis of our findings, we concluded that DAdV-3 infection is possible in chickens, and that it causes classic HHS with ulceration of the glandular stomach and a swollen bursa with petechial hemorrhages, leading to high mortality in chickens. The major variation domains did not change in Muscovy ducks or in chickens after infection. This is the first study to report DAdV-3 in chickens, providing a new basis for preventing and controlling this virus.

Protective immune response induced by Leghorn male hepatoma cell-adapted fowl adenovirus-4

Fowl adenovirus-4 (FAdV-4) is a highly contagious virus that causes acute and lethal hepatitis. It leads to substantial economic losses in the poultry industry. Among the structural proteins of FAdV-4, hexon and fiber2 are associated with immunopathogenesis. A frameshift mutation was generated in the fiber2 protein by seral passages in the Leghorn male hepatoma (LMH) cell line. Immunization using the attenuated virus (80 times passaged) before the virulent FAdV-4 challenge protected hosts from the infection and cleared the invading virus. In immunized animals, activated CD4+ and CD8+ T cell populations were larger during the FAdV-4 challenge. The change in the B cell population was similar. Myeloid cells were highly increased during FAdV-4 infection after the immunization, but the immunization inhibited the expansion in both liver and spleen. The functional gene expression for immune modulation was strongly associated with immune cell changes in the liver, however, this association was not strong in the spleen. The present findings imply that genetic modification by cellular adaptation regulates immune cell phenotype and function in the target organ. In addition, we suggest the attenuated virus as a protective strategy against the novel FAdV-4 strains.