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DUCK VIRUS HEPATITIS

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.


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