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Duck Virus Hepatitis

Duck virus hepatitis (DVH) infects mainly young ducklings only, this is due to the resistance to the virus as the duck grows older. DHAV (formerly DHV- 1) is present in Northern America, Europe and Asia, DHV-2 has only been found in the United Kingdom and DHV-3 has only been found in the United States of America. DVH can be caused by 3 different kinds of viruses, mainly the duck hepatitis A virus (DHAV), the DHV-2 and the DHV-3. DHAV is a Picornaviridae and the DHV-2 and DHV-3 are both astrovirus.

Life Cycle of Virus

Virion of DHV-1 is about 20-40 nm diameter. It is non-enveloped, icosahedral particle that is resistant to ether and chloroform. It also have the ability to survive under normal environmental condition for an extended amount of time. Genomic structure and functions are still unknown since the full genome was only discovered in 2006.

DHV-1 is the most lethal disease out of all 3 kinds, thus, this research will be focused on DHV-1.
DHV-1 can be detected through the below symptoms observed from ducks:
•Lethargy
•Anorexia
•Sudden death with opisthotonos within a few days

After death, the liver of the duck can be found to be enlarged with haemorrhagic lesions and decolouration, the spleen and kidneys can also be augmented.

Above shows an image of a liver from a duckling after death from DVH
Haemorrhagic lesions can be observed from the liver

Few methods of diagnosis of the virus includes the following :
• Duck Virus Enteritis
• Coccidiosis
• Mycotoxicosis
• Pasteurella anatipestifera
• Serology tests

Serlogical testing is the most common method of diagnosis. Serum neutralization test that takes place in ovo have been used with all the 3 serotypes and have been developed for DHV type I. It is now used for virus identification, immune responses to vaccination & epidemiological surveys.
1) By inoculation of the isolates from subcutaneous or intramuscular into ducklings between 1 & 7 day that are susceptible to DHV type I. The characteristic must matched with deaths occuring within 18-48 hours of inoculation, often less than 24 hours. Virus should be re-isolated from the livers

2) Inoculation of serial dilutions from the liver homogenate into allantoic sac of embryonated duck eggs which age between 10-14 days. It should die between 24 and 72 hours later. Embryo livers may be red and yellowish, swollen and necrotic foci is evident. Liver lesion and stunting will become more evident.

3) Inoculation of primary cultures – duck embryo liver cells, particularly sensitive. Dilution of liver homogenate which contains DHAV type 1 causes a cytopathic effect, characterized by cell rounding and necrosis. In medium containing 1% agarose (w/v), it gives rise to plaques approx. 1 mm in diameter.

There are also detection kits available for diagnosis of the virus:
• Immunological tests
• Nucleic acid recognition methods
• Polymerase chain reaction
• Detection of DHV-I from duck and chicken embryo organs and nucleic acid extraction
• Oligonucleotide primers
• One-step RT-PCR
• Detection of one-step RT-PCR products
• Interpretation of results
This disease can be transmitted easily as it is highly contagious, direct contact of each other will transmit the virus. Direct contacts include contact with excreted faeces from infected ducks and also from brooder, water, feeds and equipments.

However, there are methods of controls to this disease. One such control is to use live attenuated vaccines. These vaccines can be introduced into the breeder ducks, so that the ducklings reproduced will be maternally immune to the disease. Ducks that are susceptible may also be protected with a chicken egg yolk antibody preparation.

Humans are not susceptible to DHV of any types as it is not infectious to humans. Also, ducks tend to die at a young age that is not fitting for consumption

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