Dr. Mitun Sarkar . 20th May, 2022, 11:06 PM
DUCK VIRUS
HEPATITIS
Etiology
A picornavirus
is responsible for duck virus hepatitis Types 1 and 3. This agent is distinct
from hepadnavirus (duck hepatitis B). An astrovirus-like agent has been
implicated in outbreaks of duck virus hepatitis Type 2 in the UK.
Occurrence and
Economic Significance
Duck virus
hepatitis Types 1 and 3 occur in ducklings under 4 weeks of age in all
intensive duck-rearing areas of the world. Mortality results in extensive
losses especially with intercurrent bacterial infections including chlamydiosis,
Riemerella and E. coli infection, mycotoxicosis and environmental
stress.
Transmission
Free-living
waterfowl introduce the virus. Rodents serve as reservoir hosts on affected
farms. Direct contact between infected and susceptible flocks especially in
multiage operations predisposes to disease.
Clinical Signs
Morbidity in
susceptible flocks may range from 50% to 100%. Mortality is dependent on the
age of the flock, with losses of up to 90% in batches under one week of age,
declining in severity to under 10% at 4 weeks of age. Mortality is exacerbated
by intercurrent bacterial infections. Ducklings demonstrate peracute mortality
preceded by lateral recumbency and occasionally, opisthotonos (hyperextension
of the neck, “stargazing”).
Pathology
The significant
lesion comprises enlargement of the liver with punctate or ecchymotic
hemorrhages. In the presence of chlamydiosis or Riemerella spp
infection, airsacculitis and peritonitis may be observed.
Diagnosis
The
picoronaviruses responsible for duck virus hepatitis can be isolated from
livers using 9-day old embryonated SPF chickens inoculated by the allantoic sac
route. Serologic procedures include agar gel diffusion precipitin test, virus
neutralization in duck embryos and a plaque reduction test to quantify
neutralizing antibody.
Treatment
No specific
treatment is available. Supportive therapy is recommended.
Prevention
Hyperimmune serum from flocks surviving duck viral hepatitis can be administered to ducklings. An injection of 0.5 ml filtered serum is recommended using the intramuscular route. Breeders can be immunized with a live attenuated chicken-embryo origin vaccine. Some vaccines have shown reversion to virulence when applied to large flocks. Where possible, single-age isolated placement programs should be followed. Rodents should be eradicated.
