following inoculation with N-DRV
Infected breeding ducks were depressed and had decreased appetite. Some breeding ducks developed symptoms of diarrhea, but throughout the experiment, there was no death of infected breeding ducks. Autopsy showed that the main pathological changes in the orally administered and intramuscular injection group were atrophy of follicles (Fig 1A), bleeding of the follicular membrane (Fig 1B), hemorrhage of the fallopian tubes (Fig 1A/B), hemorrhage of the spleen (Fig 1C), and scattered bleeding points in the liver (Fig 1D). In both the orally administered and intramuscular injection group, viral RNA was detected in the ovaries and fallopian tubes of infected ducks.
In the experimental group, the size of embryonated eggs varied (Fig 2A), and the number of inconsistent shape eggs and sand-shelled eggs increased (Fig 2B). During the hatching process, difficulty in pecking the shells occurred (Fig 2D), the embryonic body of the ducklings (Fig 2E), and the liver had obvious bleeding symptoms (Fig 2F). The ducklings did not show obvious clinical symptoms except for depressed and lack of appetite (Fig 3G). With the growth of ducklings, necrosis of the spleen of the ducklings revealed several necrotic lesions of varying degrees (Fig 3H). The breeding ducks and hatchling ducklings in the control group were normal, and no pathogenic infection was detected by PCR.