An Emerging Duck Egg-Reducing Syndrome Caused by a Novel Picornavirus Containing Seven Putative 2A Peptides

Figure 1. Phylogenetic relationship between DERSV and other picornaviruses. The neighbor-joining tree was constructed according to the amino acid sequences of DERSV (AH204 strain). The numbers along the branches mark the bootstrap values percentage out of 1000 bootstrap resamplings. The scale bar indicates the number of substitutions per site.

Figure 2. Schematic diagram of whole-genome and 2A region. (A) Predicted genome organization of the DERSV. P1 represents viral structural proteins, and P2 and P3 represent non-structural proteins. The length of amino acid was indicated in each gene box. (B) Comparison of putative 2A peptides of Picornaviruses. The dot represents the absence of amino acids and the different colors in the box represent 2A1(blue), 2A2(green), 2A3(orange), 2A4(yellow), 2A5(purple), 2A6(red), 2A7(golden).

Figure 3. Predicted secondary structure of the DERSV IRES. Domains II and III are labeled according to corresponding domains in the type IV IRESs [14]. In domain III, individual helical segments are labeled III1 and III2, etc.; and individual hairpins are labeled IIIa and IIIb, etc. The pseudoknot stem 1, stem 2 and domain IIIf helix are labeled.

Figure 4. The correlation survey between the outbreaks of egg-reducing syndromes and the appearance of the specific antibodies against DERSV. In the early stage, the egg-reducing syndromes happened in one duck house. Meanwhile, the antibodies against DERSV were detectable in some serum samples, and seroconversion was found later in all the serum samples. In the other three duck houses, the egg-reducing syndromes happened one by one, and the antibodies against DERSV changed in a similar dynamic pattern as in the first duck house. The DERSV antibodies were not detected in the house without the egg-reducing syndrome.

Figure 5. Pathogenicity of DERSV ducks. (A) Infected ducks show liver and renal hemorrhage, follicular hemorrhage, and rupture. Congestion of hepatic venules and sinusoid, congestion of renal interstitium, degeneration of renal tubular epithelial cells, and Necrosis of follicular epithelial cells were detectable on the tissue sections accordingly. In addition, viral antigens could be observed in those tissues of infected ducks. (B) Virus titer in tissues of livers, kidneys, and ovaries of inoculated and exposed ducks was determined on 9-day-old embryonated duck eggs. The lower limit of virus detection was 0.5log10 EID50 per gram tissue.