Prevalence and Molecular Characteristics of FAdV-4 from Indigenous Chicken Breeds in Yunnan Province, Southwestern China

Detection and differentiation of fowl adenovirus serotype 4 and duck adenovirus 3 using high resolution melting curve assay

Fowl adenovirus type 4 (FAdV-4) and duck adenovirus type 3 (DAdV-3) are the causative agents of clinical diseases in poultry and have caused considerable economic losses to the waterfowl industry in China. Both FAdV-4 and DAdV-3 are classified into the genus Aviadenovirus under the family Adenoviridae. The high-resolution melting (HRM) assay has become a useful method for virus genotyping, which offers the possibility of rapidly developing a differentiation technique in which the melting profile depends on the GC content of the product in the qPCR platform. The aim of this study was to develop a qPCR-HRM assay for sensitive FAdV-4 and DAdV-3 detection and differentiation. Here, specific primers were designed on the basis of the 100 K genes of FAdV-4 and DAdV-3, and a qPCR-HRM assay was established through optimization of the reaction conditions. A specificity test revealed that this method could detect only FAdV-4 and DAdV-3, with no cross-reaction with other common duck-derived viruses. A sensitivity test revealed that the lowest detection limits of FAdV-4 and DAdV-3 were 2.84 copies/µL and 2.85 copies/µL, respectively. A repeatability test demonstrated that the coefficient of variation was less than 2.5 % in both the intragroup and the intergroup analyses. Field sample distributions of FAdV-4 and DAdV-3 were investigated, and the percentages of DAdV-3-positive, FAdV-4-positive and coinfection-positive in Muscovy ducks were 27.78 %, 16.67 % and 11.11 %, respectively. Further studies are needed to provide more insight into the pathogenesis of FAdV-4 and DAdV-3 coinfection in ducks. In conclusion, the qPCR-HRM assay provides an accurate, sensitive, reliable and cost-effective alternative method for detecting and distinguishing FAdV-4 and DAdV-3.

Chicken Interferon-Alpha and -Lambda Exhibit Antiviral Effects against Fowl Adenovirus Serotype 4 in Leghorn Male Hepatocellular Cells

Hydropericardium hepatitis syndrome (HHS) is primarily caused by fowl adenovirus serotype 4 (FAdV-4), causing high mortality in chickens. Although vaccination strategies against FAdV-4 have been adopted, HHS still occurs sporadically. Furthermore, no effective drugs are available for controlling FAdV-4 infection. However, type I and III interferon (IFN) are crucial therapeutic agents against viral infection. The following experiments were conducted to investigate the inhibitory effect of chicken IFN against FadV-4. We expressed recombinant chicken type I IFN-α (ChIFN-α) and type III IFN-λ (ChIFN-λ) in Escherichia coli and systemically investigated their antiviral activity against FAdV-4 infection in Leghorn male hepatocellular (LMH) cells. ChIFN-α and ChIFN-λ dose dependently inhibited FAdV-4 replication in LMH cells. Compared with ChIFN-λ, ChIFN-α more significantly inhibited viral genome transcription but less significantly suppressed FAdV-4 release. ChIFN-α- and ChIFN-λ-induced IFN-stimulated gene (ISG) expression, such as PKR, ZAP, IRF7, MX1, Viperin, IFIT5, OASL, and IFI6, in LMH cells; however, ChIFN-α induced a stronger expression level than ChIFN-λ. Thus, our data revealed that ChIFN-α and ChIFN-λ might trigger different ISG expression levels, inhibiting FAdV-4 replication via different steps of the FAdV-4 lifecycle, which furthers the potential applications of IFN antiviral drugs in chickens.