Pharyngeal swabs from all inoculated ducks were positive
(Ct < 40) at 1 dpi by RT-PCR and remained positive until the day of
euthanasia (3 or 4 dpi) (Table 1). All cloacal swabs were negative
except one from duck 2 at 2 dpi. Virus titers in the swabs ranged
from 100.8 to 106.2 TCID50/ml of transport medium (Table 1). Virus
was found in one plasma sample (duck 4) collected at the time of
euthanasia.
Clinical signs were noted from 2 dpi. The ducks became restless
and two of them (ducks 1 and 4) began showing mild neurological
signs, including twitching of a wing and occasional jerky movements
of the head. By 3 dpi, three ducks (ducks 1, 3, and 4) had
developed more severe clinical signs including staggering gait and
protrusion of the third eyelid. In duck 4, neurological signs
aggravated during the day (head and body tremors, ataxia, and
abnormal head posture during ambulation) and it was therefore
euthanized at 3 dpi instead of at 4 dpi. Ducks 1 and 3 showed
similar neurologic signs at 4 dpi as they had at 3 dpi. Duck
2 showed increased restlessness at 3 and 4 dpi but did not have any
other detectable clinical signs. A progressive decrease in feed
consumption was noted and there was an average decrease in body
weight of 88 g (560–472 g) from 0 dpi to 4 dpi. Control birds did not
show any clinical signs and gained an average of 30 g body weight
during this time.