Abstract
Hydropericardium hepatitis syndrome (HHS) caused by group I fowl adenovirus serotype 4 (FAdV-4) is an acute and infectious disease in fowl, particularly in broilers aged 3–5 weeks. In June 2015, a highly pathogenic disease outbroke in 25–40 day-old ducklings in Shandong province, characterized similar symptom to HHS. In order to determine the pathogenic mechanism of FAdV-4 (SDSX strain) in meat ducks. We divided 90 25-day-old Cherry Valley meat ducks into three groups (oral, subcutaneous, and control; 30 ducks in each group) and infected them with the virus. HHS, inclusion body hepatitis, and enlargement and hemorrhage of the spleen, kidney, lung, thymus, and brain were observed in FAdV-4-infected meat ducks. Histopathological changes were mainly characterized by severe fatty degeneration in the liver, basophilic inclusion bodies in hepatocytes, and vacuolation in the bursa. More importantly, viral DNA could be detected by quantitative real-time polymerase chain reaction in several viscera tissues (e.g., heart, liver, spleen) on the third day after infection. Notably, the livers of the two infected groups contained the highest concentration of viral DNA. In addition, immune responses were studied based on titer levels of the virus antibody and the levels of inflammatory cytokines interleukin (IL)-2 and interferon (IFN)-γ, and most levels were significantly upregulated, indicating that the host immune responses were activated early in infection. These findings increase our understanding of the pathogenicity of FAdV-4 (SDSX) in meat ducks and provide the foundation for further in-depth study of the pathogenic mechanism of this virus.
Highlights
Fowl adenovirus serotype-4 (FAdV-4) is a member of the Aviadenovirus genus, Adenoviridae family, and contains non-enveloped and double-stranded DNA with a genome of approximately 43–46 kb that encodes 11 non-structural proteins [E1A, E1B, E2A (DBP), E3 (ADP), E4, EP, 33 K, 52/55 K, pol, pIVaII, and 100 K] and 10 primary structural proteins
Little is known about the pathogenicity of this virus in Cherry Valley meat ducks, except that intracerebral infection caused a 15% mortality rate (Chen et al, 2016) and oral infection showed no clinical signs (Pan et al, 2017); to complete the pathogenicity of the virus, Cherry Valley meat ducks were infected with fowl adenovirus serotype 4 (FAdV-4) in this study
Cloacal/tracheal swabs and serum samples were collected from ducks and tested by polymerase chain reaction (PCR) to confirm that they were free of FAdV-4 infection
Summary
Griffin and Nagy, 2011; Xie et al, 2013; Li et al, 2017) This virus can cause acute avian infectious diseases such as hydropericardium hepatitis syndrome (HHS), inclusion body hepatitis (IBH), and gizzard erosion in duck layers and broilers (Marek et al, 2012; Chen et al, 2016). Among these diseases, HHS was first reported in Angara Goth ( named Angara disease), Pakistan in 1987 and subsequently broke out in North America, Mexico, Eastern Europe, India, South Asia, China, Japan, and South Korea, causing economic losses mainly to the broiler industry worldwide (Al-Sadi et al, 2000; Kim et al, 2008; Mase et al, 2009; Kaján et al, 2013; Niczyporuk, 2016). This study laid the foundation for further in-depth study of the pathogenic mechanism of FAdV-4 and contributed to the control of this contagious disease
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