Antibody Response and Virus Shedding of Chickens Inoculated with Left End Deleted Fowl Adenovirus 9-Based Recombinant Viruses

Identification of four serotypes of fowl adenovirus in clinically affected commercial poultry co-infected with chicken infectious anaemia virus in Trinidad and Tobago

Fowl adenovirus (FAdV), which causes the high-impact diseases such as inclusion body hepatitis and hepatitis-hydropericardium syndrome, is of major concern to the poultry industry internationally. This study was carried out in direct response to mortality rates of up to 75% in commercial broiler flocks in Trinidad, West Indies. Symptoms in 3- to 8-week-old broilers and 13- to 18-week-old pullets pointed to infection with an immunosuppressive viral pathogen. The objectives of the study were to determine whether the infectious agent FAdV, along with other viral pathogens, was responsible for the clinical disease, and to obtain information on the serotypes of FAdV that were infecting the birds. Tissue samples from clinically affected birds from eight different farms were tested for chicken infectious anaemia virus (CIAV) and infectious bursal disease virus (IBDV) by real-time reverse transcription polymerase chain reaction (PCR) and for FAdV by conventional PCR. The birds tested positive for FAdV and CIAV, but negative for IBDV. The gene corresponding to the L1 loop of the hexon protein for FAdV was amplified and sequenced. Phylogenetic analysis of seven FAdV strains inferred that four serotypes were likely to be circulating in the chickens. Well supported genetic relatedness was observed for serotype 8a (97.8%), 8b (97.8%), 9 (95.8%) and 11 (98.8%-99.5%). This is the first published report from Trinidad and Tobago on the presence and circulation of pathogenic FAdV strains, in combination with CIAV, in poultry. The data demonstrate a possible need for the introduction of serotype-specific vaccines against FAdV, as well as vaccines against CIAV, in broilers in the region and emphasize the importance of maintaining high levels of biosecurity on farms to prevent the spread of these potentially devastating viruses between farms.

Generation and characterization of a fowl adenovirus 9 dual-site expression vector

Fowl adenoviruses (FAdVs) are widely considered as excellent platforms for vaccine development and gene therapy. We improved on our right-end partial TR-2 deleted or a left-end 2.3 kb deleted vectors by developing a single, dual-site delivery vector. We demonstrated that, in addition to ORF11, the right end ORF17 is also dispensable. To further improve the capacity and flexibility of the FAdV-9 based vector system, we generated an infectious recombinant FAdV-9 dual-site expression clone lacking 1.9 kb of the left end and replaced with mCherry under the control of a native promoter, and 3.6 kb of the right-end replaced with an EGFP expression cassette. Five intermediate FAdmid clones were successfully constructed: a) pFAdV-9Δ0-2RED (mCherry replacing the left end 2.2 kb ORF0 to 2); b) pFAdV-9RED (mCherry replacing the left end 1.9 kb ORF1 to 2); c) pFAdV-9Δ17 (deletion of ORF17 and 393 bp downstream untranslated region); d) pFAdV-9GFP (EGFP expression cassette replacing the right end 3.6 kb) and e) pFAdV-9Dual (both mCherry in the left end and the EGFP expression cassette in the right end of our vector). Our novel FAdV-9 dual-site vaccine vector, produced infectious virus and expressed either one or both mCherry and EGFP.

Fowl Adenovirus-Based Vaccine Platform

Nonpathogenic fowl adenoviruses (FAdVs) are amenable for engineering multivalent vaccine platforms due to large stretches of nonessential DNA sequences in their genomes. We describe the generation of FAdV-9-based vaccine platforms by targeted homologous recombination in an infectious clone (pPacFAdV-9 or wild type FAdmid) containing the entire viral genome in a cosmid vector. The viral DNA is subsequently released from the cosmid by restriction enzyme digestion followed by transfection in a chicken hepatoma cell line (CH-SAH). Virus is harvested, propagated, and verified for foreign gene expression.

Oral inoculation of chickens with a candidate fowl adenovirus 9 vector

Fowl adenoviruses (FAdVs) are a potential alternative to human adenovirus-based vaccine vectors. Our previous studies demonstrated that a 2.4-kb region at the left end of the FAdV-9 genome is nonessential for virus replication and is suitable for the insertion or replacement of transgenes. Our in vivo study showed that the virus FAdV-9Δ4, lacking six open reading frames (ORFs) at the left end of its genome, replicates less efficiently than wild-type FAdV-9 (wtFAdV-9) in chickens that were infected intramuscularly. However, the fecal-oral route is the natural route of FAdV infection, and the oral administration of a vaccine confers some advantages compared to administration through other routes, especially when developing an adenovirus as a vaccine vector. Therefore, we sought to investigate the effects of FAdV-9 in orally inoculated chickens. In the present study, we orally inoculated specific-pathogen-free (SPF) chickens with FAdV-9 and FAdV-9Δ4 and assessed virus shedding, antibody response, and viral genome copy number and cytokine gene expression in tissues. Our data showed that FAdV-9Δ4 replicated less efficiently than did wtFAdV-9, as evidenced by reduced virus shedding in feces, lower viral genome copy number in tissues, and lower antibody response, which are consistent with the results of the intramuscular route of immunization. Furthermore, we found that both wtFAdV-9 and FAdV-9Δ4 upregulated the mRNA expression of alpha interferon (IFN-α), IFN-γ, and interleukin-12 (IL-12). In addition, there was a trend toward downregulation of IL-10 gene expression caused by both viruses. These findings indicate that one or more of the six deleted ORFs contribute to modulating the host response against virus infection as well as virus replication in vivo.