Pathobiological characterization of a novel duck picornavirus in duck in China

Abstract

A novel strain of duck picornavirus was isolated from duck tissue in Taian, Shandong Province, in 2017 in our laboratory. The virus was amplified in specific-pathogen-free (SPF) chicken embryos, purified and then analyzed by whole genome sequencing, which revealed a new duck-derived small RNA virus that was designated as Duck/FC22/China/2017 (FC22, GenBank accession no. MN102111) based on its genome structure and phylogenetic relationship. An in-depth study revealed that the virus grew well on the Leghorn male hepatoma (LMH) cell line. After propagation of the virus, SPF ducks were inoculated for pathogenicity tests, and their mental state, growth and development were observed after inoculation; the ducks were dissected to observe the organs and histopathological changes. A TaqMan fluorescence quantitative PCR method was utilized to detect the proliferation and shedding patterns of the virus within the ducks, while the SYBR Green I fluorescence quantitative PCR method was used to assess cytokine expression levels in the organs. The results showed that following inoculation with the FC22 strain, the mental status of the SPF ducks remained unchanged. Mild oedema was observed in some tissue organs during dissection; however, no pathological changes, such as congestion or degeneration, were noted. Histopathological analysis revealed cellular necrosis in organs, including the heart, liver, and bursa of Fabricius, as well as a reduced volume and deep staining of certain neurons in the cerebrum. Following infection, the virus titres in various organs and in cloacal swabs of the SPF ducks peaked on the first day before gradually decreasing daily. By the 10th d, the virus titres in all organs had decreased to less than 10¹ copies/μL. Additionally, notable alterations were observed in the expression levels of the cytokines IFNα, IL6, IL10, and TNFα. This indicates that the FC22 strain does not cause significant disease in ducks. This report presents the initial study on a recently discovered picornavirus, offering a thorough and methodical examination of its pathogenic characteristics and provides a reference for the clinical evaluation and scientific strategies for the prevention and treatment of this particular picornavirus.

Keywords: Duck picornavirus; change in cytokine; pathogenicity test; virus proliferation.

Figure 1

FC22 induced lesions in LMH cells. (A) FC22 infection group (72 h); (B) Control group (72 h).

Figure 2

SPF duck weight changes.

Figure 3

Variation in SPF duck organ coefficients. (A): heart; (B): liver; (C): spleen; (D): lungs; (E): kidneys; (F): cerebrum.

Figure 4

Histopathological changes in the organs of SPF ducks 1 d after inoculation (400 ×). (A): Intramuscular inoculation; (B): Intracerebral inoculation; (1): heart; (2): spleen; (3): cerebrum; (4): kidneys.

Figure 5

Histopathological changes in the organs of SPF ducks 3 d after inoculation (400 ×). (A): Intramuscular inoculation; (B): Intracerebral inoculation; (1): heart; (2): kidneys; (3): cerebrum; (4): liver; (5): spleen.

Figure 6

Histopathological changes in the organs of SPF ducks at 7 d after inoculation (400 ×). (A): Intramuscular inoculation; (B): Intracerebral inoculation; (1): heart; (2): cerebrum; (3): liver.

Figure 7

Viral load and viral clearance capacity of organs in SPF ducks. (A): Intramuscular inoculation; (B): Intracerebral inoculation.

Figure 8

Cytokines changes in in organs of intramuscularly inoculated SPF Ducks. (A): liver; (B): cerebrum.