Pathogenicity Evaluation and Virulence Gene Identification of an Attenuated Duck Enteritis Virus

Figure 1. Viral growth kinetics. CEF was infected with E74 or E1 (MOI = 0.001), the supernatants were collected at the indicated time points for virus titration in CEF cells. The data for virus titers indicate the means of the results of three repeats, and the error bars indicate standard errors of the means (***, p < 0.001).

Figure 2. The Pathogenicity of the E74 and E1 in Ducks. Eight 8−day−old Shelducks were inoculated i.m. with 105.0 TCID50 of E74 or E1. (a) The lesions of livers and spleens of ducks inoculated with the E1 and E74 at 4 dpi. (b) The virus titers in all three ducks sampled at 4 dpi. The data for the virus titers indicate the means of the results of three ducks, and the error bars indicate standard errors of the means (**, p < 0.01; ***, p < 0.001; ****, p < 0.0001). (c) The survival rates of ducks were monitored daily for 14 consecutive days. (d) Serum antibody responses against DEVs were detected at 0 and 7 dpi. Serum was considered positive when the PI value was ≥21.6%. (e) Histopathological examination (H&E staining) in the livers and spleens of ducks inoculated with the E74 and E1. Magnification: 20×.

Figure 3. The comparison of genomic organization between the E1 strain and the E74 strain. (a) The E74 strain exhibits a gene deletion in the UL region. (b) The recombinant viral strain rE1-Δ5152 was generated by deleting a 5152-bp fragment in the UL region of the E1 strain. (c) Schematic diagram of recombinant virus rescue. (d) Detection via IFA with anti-DEV monoclonal antibody at 48 hpi after rE1-Δ5152 recombinant virus infection in CEF cells. (e) A 5152-bp deletion in the UL region of the recombinant virus was verified by PCR.

Figure 4. The Pathogenicity of the E1 and rE1-Δ5152 in Ducks. Six 8-day-old Shelducks were inoculated i.m. with 105.0 TCID50 of E1 or rE1-Δ5152. (a) The lesions of livers and spleens of ducks inoculated with the E1 and rE1-Δ5152 at 4 dpi. (b) The virus titers in all three ducks sampled at 4 dpi. The data for the virus titers indicate the means of the results of three ducks, and the error bars indicate standard errors of the means **, p < 0.01; ***, p < 0.001; ****, p < 0.0001). (c) The survival rates of ducks were monitored daily for 14 consecutive days. (d) Histopathological examination (H&E staining) in the livers and spleens of ducks inoculated with the E1 and rE1-Δ5152. Magnification: 20×.