Efficacy, humoral, and cell-mediated immune response of inactivated fowl adenovirus 8b propagated in chicken embryo liver cells using bioreactor in broiler chickens

Safety and Immunogenicity of Inactivated Fowl Adenovirus Serotype 8b Isolate Following Different Inactivation Time Intervals in Broiler Chickens

In recent years, significant attention has been directed towards the development of inactivated fowl adenovirus (FAdV) vaccines within the poultry industry to combat outbreaks of inclusion body hepatitis (IBH). This study aimed to assess the safety and immunogenicity of an inactivated FAdV vaccine following different inactivation time intervals in commercial broiler chickens. The FAdV isolate UPM1137 was treated with binary ethyleneimine (BEI) at intervals of 20, 24, 28, 32, and 36 hours. All treated isolates underwent safety testing in specific pathogen-free (SPF) chicken embryonated eggs (CEE), followed by safety and immunogenicity trials in SPF chickens. The findings demonstrated that isolates treated at 20, 24, and 28 hours induced over 80% mortality in SPF CEE, while no mortality was observed in isolates treated at 32 and 36 hours. In SPF chickens, there were no clinical signs or gross and histological lesions recorded throughout the trial for those inoculated with isolates treated at 32 and 36 hours, indicating that these treatments rendered the virus completely inactivated and safe for use in commercial broiler chickens. Based on ELISA results, chickens vaccinated with the inactivated FAdV at 32 hours (group B) exhibited a higher antibody response compared to those vaccinated with the inactivated FAdV at 36 hours (group A) at days 14 and 28 post-inoculation (pi). At day 28 pi, the mean antibody titers for the booster groups in both group A and group B were significantly higher (p < 0.05) compared to the control group. These results indicate that both FAdV vaccines, using inactivated inocula at 32 and 36 hours, are safe and immunogenic in broiler chickens, particularly by day 28 pi following booster vaccination. Thus, it was concluded that the optimal duration for FAdV inactivation is 32 hours, making it highly suitable for future vaccine formulations.

Molecular Epidemiology of Fowl Aviadenoviruses in Broiler Chickens from Vaccinated and Nonvaccinated Breeders

Fowl aviadenoviruses (FAdVs) are widely distributed among poultry populations, leading to various diseases, immunosuppression, and economic losses. Molecular characterization and phylogenetic analysis of circulating FAdV isolates play a critical role in epidemiologic studies, contributing to the control, monitoring, and prevention of related outbreaks. This study aimed to determine the serotypes of FAdV and reveal the molecular epidemiology in broiler chicken flocks. Samples were taken based on epidemiologically important parameters, such as vaccination status, age, and transmission route. A total of 20 vaccinated flocks (VF, flocks originated from vaccinated breeder lines) and 20 nonvaccinated flocks (NVF, flocks originated from nonvaccinated breeder lines) were randomly selected from flocks reporting suspected FAdV clinical symptoms and deaths. Vaccination was administered by intramuscular injection into the pectoral muscle with a commercial inactivated vaccine at 12 and 18 wk. Liver and cloacal swab samples were collected from each flock over two different production cycles and for three different age groups (1-day-old, 14-day-old, and 28-day-old chickens). The liver and cloacal swap samples were analyzed for FAdV using PCR targeting the hexon loop-1 gene. Molecular detection revealed that 30.0% (24/80) of all flocks were FAdV positive, with 50.0% (20/40) positivity in NVF and 10.0% (4/40) in VF. Sequence analysis of the hexon loop-1 gene revealed that all samples were FAdV-8b serotype (OR670689-OR670712), with 100.0% similarity. One randomly selected FAdV-8b sample was analyzed by whole-genome sequence analysis. This is the first study in Turkey to deposit an FAdV whole-genome sequence (44,139 bp) into the GenBank database (PP236873). Given the significantly lower FAdV positivity rates in VF compared to NVF, the findings indicate that vaccination is an effective tool for protecting against FAdV-related infections.

Humoral, cellular immunity and efficacy of bioreactor propagated and inactivated Fowl adenovirus 8b adjuvanted with Montanide 71VG in broiler chickens

Objectives

The study aimed to inactivate the FAdV isolate (UPM11142P5B1) produced in a bioreactor and assess the humoral and cellular immunity, efficacy, and virus shedding in broiler chickens.

Materials and Methods

The isolate was grown in a bioreactor, inactivated using binary ethyleneimine, adjuvanted with Montanide 71VG, and injected into day-old broiler chickens either with or without booster groups. The following parameters were measured: T lymphocyte profile in the liver, spleen, and thymus; FAdV antibody titer; clinical symptoms; gross and histological alterations in the liver, spleen, and thymus; virus copy number in the liver and cloacal shedding.

Results

Compared to the unchallenged control group, booster (BG), and non-booster (NBG), the challenged control group (CCG) had a larger liver: body weight (BW) ratio, milder clinical signs, gross lesions, and histological alterations. They also had a lower BW. At 7, 21, 35, and 42 days post-inoculation (dpi), the NBG and BG exhibited higher antibody levels than the UCG. At 35 dpi, challenged BG and NBG produced more antibodies than CCG. In BG and NBG, T cells were stimulated in the spleen, thymus, and liver. At 35 and 42 dpi, the challenged BG and NBG showed significantly decreased viral copy numbers in the liver and shedding, respectively, along with increased lymphocyte counts.

Conclusion

The inactivated UPM11142P5B1 with Montanide 71VG could be a vaccine against FAdV 8b infections in chickens.

Attenuation and molecular characterization of fowl adenovirus 8b propagated in a bioreactor and its immunogenicity, efficacy, and virus shedding in broiler chickens

Background and Aim

Live-attenuated vaccines are the most successful type of vaccine and could be useful in controlling fowl adenovirus (FAdV) 8b infection. This study aimed to attenuate, molecularly characterize, and determine the immunogenicity, efficacy, and challenge virus shedding in broiler chickens.

Materials and Methods

The FAdV 8b isolate (UPM08136) was passaged onto chicken embryo liver (CEL) cells until attenuation. We sequenced and analyzed the hexon and fiber genes of the passage isolates. The attenuated bioreactor-passage isolate was inoculated into 1-day-old broiler chickens with (attenuated and inactivated) and without booster groups and challenged. Body weight (BW), liver weight (LW), liver: body weight ratio (LBR), FAdV antibody titers, T-lymphocyte subpopulation in the liver, spleen, and thymus, and challenge virus load and shedding were measured.

Results

Typical cytopathic effects with novel genetic changes on CEL cells were observed. The uninoculated control-challenged (UCC) group had significantly lower BW and higher LW and LBR than the inoculated groups. A significantly higher FAdV antibody titer was observed in the challenged non-booster and attenuated booster groups than in the UCC group. T cells in the spleen and thymus of the liver of inoculated chickens were higher than uninoculated control group levels at all-time points and at different times. A significantly higher FAdV challenge virus load was observed in the liver and shedding in the cloaca of UCC chickens than in non-booster chickens.

Conclusion

The FAdV 8b isolate was successfully attenuated, safe, and immunogenic. It reduces virus shedding and is effective and recommended as a vaccine against FAdV infection in broiler chickens.

Efficacy, immunogenicity, and virus shedding in broiler chickens inoculated with live attenuated fowl adenovirus serotype 8b propagated a bioreactor

Background

Fowl adenovirus (FAdV) 8b causes huge economic losses in the poultry industry worldwide. Attenuated FAdV 8b could be useful in preventing FAdV infections globally and scale-up obstacles could be solved by bioreactor technology.

Aim

This study was carried out to attenuate the FAdV 8b isolate, propagate it in a bioreactor, molecularly characterize the passage isolates, and determine the immunogenicity, efficacy, and shedding of the virus of chickens.

Methods

FAdV serotype 8b (UPM11142) isolate was passaged on chicken embryo liver (CEL) cells until attenuation and propagated in a bioreactor (UPM11142P20B1). Hexon and fiber genes of the isolates were sequenced and analyzed. UPM11142P20B1 was administered to 116-day-old broiler chickens divided into four groups, A (control), B (non-booster), C (booster with UPM11142P20B1), and D (booster with inactivated UPM11142P5B1). Eight chickens from each group were challenged. Body weight (BW) and liver weight (LW), liver: BW ratio (LBR), FAdV antibody titer, T lymphocyte sub-populations in the liver, spleen and thymus; and challenge virus load in the liver and shedding in cloaca were measured at weekly intervals.

Results

The isolate caused typical cytopathic effects on CEL cells typical of FAdV. Novel molecular changes in the genes occurred which could be markers for FAdV 8b attenuation. BW, LW, and LBR were similar among groups throughout the trial but the uninoculated control-challenged group (UCC) had significantly higher LBR than the inoculated and challenged groups at 35 dpi. Non-booster group had higher FAdV antibodies at all time points than the uninoculated control group (UCG); and the challenged booster groups had higher titer at 35 dpi than UCC. T lymphocytes increased at different time-points in the liver of inoculated chickens, and in the spleen and thymus as well, and was higher in the organs of inoculated challenged groups than the UCC. There was a significantly higher challenge virus load in the liver and cloaca of UCC chickens than in the non-booster chickens.

Conclusion

UPM11142P20B1 was safe, efficacious, significantly reduced shedding, and is recommended as a candidate vaccine in the prevention and control of FAdV 8b infections in broiler chickens.