Causative agent 
- DVH can be caused by any of three different
  viruses : DVH virus type 1 (picornavirus),
                DVH virus type 2 (astrovirus),
                DVH virus type 3, (picornavirus
                antigenically unrelated to DVH virus
                type 1)



Differential diagnosis 
- Salmonellosis
- Aflatoxicosis



1. History taking 
- Occurs in ducklings under 6 weeks of age
- Very rapid onset and spread of the disease
- DVH type 1 mortality rate in young duckling less
  than 3 weeks is 50-95% in 4-5 weeks is very low
  or negligible



2. Clinical examination 
- Birds fall on their sides, kick spasmodically with
  both legs and die with head drawn back in the
  opisthotonus



3. Necropsy 
- Enlarged liver with punctate or ecchymotic
  hemorrhages
- Sometimes enlarged and mottled spleen



4. Histopathological obersvation 
- Necrosis of hepatocytes and proliferation of the
  bile duct epithelium
- Hemorrhage and variable degree of inflammatory
  response

5. Virus isolation 
Specimen : liver, blood
Method    :
1. egg inoculation : chick embryo at 9-11 days of
    age by CAC route, duck embryo at 10-14 days of
    age by CAC or CAM route and observation of
    death with stunting, edema and subcutaneous
    hemorrhages
2. DEL. inoculation and CPE observation
    (rounding and necrosis)
3. duckling inoculation at 1-7 days of age and
    observation of death after 18 - 48 hours post
    inoculation with characteristic clinical sign and
    gross pathology



6. Virus identification 
- SN test



Control 
- Vaccination with attenuated vaccine



Note 
- DVH type 1 worldwide distribution
- DVH type 2 only in England
- DVH type 3 only in the United States, DVH type
  3 less virulent than DHV type 1