Novel duck hepatitis A virus type 1 isolates from adult ducks showing egg drop syndrome.

Generally, duck hepatitis A virus type 1 (DHAV-1) only infects young ducklings. Since December 2016, severe outbreaks of duck viral infection with egg drop, feed consumption decline, and ovary-oviduct disease have occurred in some laying duck flocks in Shandong Province of China. DHAV-1 isolated from the affected ducks was confirmed as the causative pathogen of the egg drop. Compared with other DHAV-1 strains, the novel isolate has three special amino acid mutation points in the most variable regions at the C-terminus of VP1. The experimental infection in laying ducks indicated that successful immunization with DHAV-1 vaccine could protect laying duck from infection. To the best of our knowledge, this is the first reported incidence of a severe duck disease outbreak involving egg drop syndrome caused by DHAV-1.