Isolation and molecular characterization of prevalent Fowl adenovirus strains in southwestern China during 2015–2016 for the development of a control strategy

Figure 1. The score reference of gross lesions in liver, heart and kidney from chickens. The killed and dead birds of all groups were scored using this standard. Gross lesions of livers were scored as follow: 0 for normal (A-0), 1 for extensive focal lesions (A-1, white arrow), 2 for diffuse lesions (A-2, white arrow). Gross lesions of the heart were scored as follows: 0 for normal (B-0), 1 for v ≤2 mL of pericardial effusion (B-1, white arrow), and 2 for v >2 mL of pericardial effusion (B-2, white arrow). Gross lesions of kidneys were scored as follow: 0 for normal (C-0), 1 for slight swelling (C-1, white arrow) and 2 for severe swelling (C-2, white arrow).

Figure 2. The immune and challenge schedule. Groups a and b: Birds were vaccinated at an age of 17 days and challenged with FAdV-4 strain at 38 days (a) and 60 days of age (b). Groups c and d: Birds were challenged with FAdV-4 strain at an age of 38 days (c) and 60 days (d). Groups e and f: Birds were vaccinated at an age of 17 days and challenged with FAdV-8a strain at 38 days (e) and 60 days (f). Groups g and h: Birds were challenged with FAdV-8a strain at an age of 38 days (g) and 60 days (h). Group i: Birds were vaccinated at an age of 17 days. Group j: Non-vaccination and non-challenge group.

Figure 3. Phylogenetic analysis of the hexon loop-1 gene from 22 wild strains (filled triangles) and 22 reference strains of FAdVs, starting at the 145AAGT- and ending at -ACTA1027 (refer to FAdV-4 strains). The phylogenetic tree was constructed using MEGA version 7.0.14 with the neighbor-joining method and 1000 bootstrap replicates.

Figure 4. Pathogenicity of serotype-2, -4, -8a and -8b strains in Partridge Shank broilers. (A) Percent survival of chickens challenged by the four serotypes, respectively. The comments in brackets indicate the serotype of the challenge strains. (B) Mean lesion scores of chickens challenged by each of the four serotypes, respectively. Mean lesion scores reflected the mean scores of gross lesions.

Figure 5. Protective efficacy of inactivated FAdV-4 vaccine against the FAdV-4 and FAdV-8a virulent challenge. (A) The mean lesions scores of vaccinated group (a and b) and unvaccinated group (c and d) challenged with the FAdV-4 strain. There were no lesions in the liver, heart and kidney in groups a and b, whereas birds in groups c and d showed severe lesions. (B) The viral detection rate in cloacal swabs of the vaccinated group (a and b) and unvaccinated group (c and d) challenged with the FAdV-4 strain. The viral detection rate in cloacal swabs of groups a and b were highly significantly different compared with groups c and d. (C) The mean lesion scores of the vaccinated groups (e and f) and unvaccinated groups (g and h) challenged with FAdV-8a strain. The vaccine significantly reduced the lesions caused by FAdV-8a. (D) The viral detection rate in cloacal swabs of vaccinated (e and f) and unvaccinated groups (g and h) challenged with FAdV-8a strain. The vaccine significantly reduced the rate of viral detection in cloacal swabs challenged with the FAdV-8a strain. *P<0.001 was considered very highly significant.