Abstract
Recently, the outbreaks of hydropericardium-hepatitis syndrome (HHS) caused by the highly pathogenic fowl adenovirus serotype 4 (FAdV-4) have resulted in huge economic losses to the poultry industry globally. Although several inactivated or subunit vaccines have been developed against FAdV-4, live-attenuated vaccines for FAdV-4 are rarely reported. In this study, a recombinant virus FA4-EGFP expressing EGFP-Fiber-2 fusion protein was generated by the CRISPR/Cas9 technique. Although FA4-EGFP shows slightly lower replication ability than the wild type (WT) FAdV-4, FA4-EGFP was significantly attenuated in vivo compared with the WT FAdV-4. Chickens infected with FA4-EGFP did not show any clinical signs, and all survived to 14 day post-infection (dpi), whereas those infected with FAdV-4 showed severe clinical signs with HHS and all died at 4 dpi. Besides, the inoculation of FA4-EGFP in chickens provided efficient protection against lethal challenge with FAdV-4. Compared with an inactivated vaccine, FA4-EGFP induced neutralizing antibodies with higher titers earlier. All these data not only provide a live-attenuated vaccine candidate against the highly pathogenic FAdV-4 but also give a potential insertion site for developing FAdV-4-based vaccine vectors for delivering foreign antigens.
Highlights
Fowl adenoviruses (FAdV) are non-enveloped viruses with a double-stranded DNA genome, belonging to Adenoviridea and genus Aviadenovirus [1]
It is noteworthy that the recent outbreaks of hepatitis-hydropericardium syndrome (HHS) caused by the highly pathogenic fowl adenovirus serotype 4 (FAdV-4) have resulted in huge economic losses to the poultry industry worldwide [7–10]
The virus plagues with EGFP could be found in the transfected leghorn male hepatoma (LMH) cells with the infection of FAdV-4 at 24 hpi, whereas no EGFP could be observed in the FAdV-4 infected LMH cells without the transfection of sgRNA and donor plasmid (Figure 1B), indicating the recombinant virus FA4-EGFP was efficiently generated
Summary
Fowl adenoviruses (FAdV) are non-enveloped viruses with a double-stranded DNA genome, belonging to Adenoviridea and genus Aviadenovirus [1]. Based on the profile of restriction enzyme digestion and the sera cross-neutralization assay, FAdV has been clustered into 5 species (FAdV-A ~ E) with 12 serotypes (FAdV-1 to 8a and 8b to 11) [2]. The infection of FAdV mainly causes clinical symptoms, including inclusion body hepatitis (IBH), hepatitis-hydropericardium syndrome (HHS), and gizzard erosion and ulceration (GEU) [3]. Among the 12 serotypes of FAdV, FAdV-4 is the main causative agent for HHS in chickens [4–6]. It is noteworthy that the recent outbreaks of HHS caused by the highly pathogenic FAdV-4 have resulted in huge economic losses to the poultry industry worldwide [7–10]. Many inactivated or subunit vaccines have been developed to control HHS [3]. The live-attenuated vaccine against FAdV-4 has rarely been reported [11, 12]
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