2.1. Detection of the DuCV genome by PCR

DNA was extracted from duck spleen tissues using a virus DNA kit (Tiangen Co., Ltd, Beijing, China). The PCR detection primers and thermal cycling were performed as described previously (Li et al., 2014). One of the DuCV-positive spleen samples from a Pekin duckling was used to amplify the full-length genome with overlapping primers DuCV-CX-F (5′-TGGCTCTCTCGTGCCCGGGGATCT-3′) and DuCV-CX-R (5′-AGGCTCTTCCTCCCAGCGACT-3′). The sequenced genome of the strain SXD1 was deposited in GenBank.