| DHV-I, DHV-Ia, DHV-II DHV-III, and DHBV | |
|---|---|
| Virus classification | |
| Group: | Group IV ((+)ssRNA) |
| Family: | Picornaviridae, Hepadnaviridae (DHBV) |
| Genus: | Enterovirus |
| Species: | Duck Hepatitis Virus I, Ia, II, III, and Duck Hepatitis B Virus |
Contents |
Duck hepatitis is caused by the enteroviruses DHV-1 and DHV-3. It is a fatal disease of ducklings causing opisthotonus and hepatitis. DHV-1 is found worldwide and causes disease in young ducklings, usually <6 weeks of age and spreads rapidly within a flock. It is the most virulent of the DHV species. DHV-3 has only been reported in the USA.
Causing acute and fatal disease in ducklings, duck hepatitis virus, DHV-1, is a Picornavirus that is distributed all over the world having significant impact on the poultry industry. First being recorded in 1949 in Long Island, New York, it was not until 57 years later in 2006 that the full genome of the pathogen was determined. This genome is composed of 7691 nucleotides and encodes and polyprotein of 2250 amino acids [1].
Duck hepatitis virus, DHV, type 1 (DHV-1), type 1a (DHV-1a), type 2 (DHV-2), and type 3 (DHV-3) are the four types of viruses that can cause disease in ducks. The pathology and pathogenicity between duck hepatitis virus type 1 and type 1a is, in essense, the same as one another [2].
Duck Hepatitis is a Class B disease listed by the Office des International Epizooties. The disease is not considered a zoonosis.
Duck hepatitis B virus, or DHBV, is a part of the Hepadnaviridae family that also comprises human Hepatitis B virus and Woodchuck hepatitis virus. It is vastly found among the wild and domestic duck population due to being passed on in utero. Duck hepatitis B virus is the first of its kind to utilize an avian host where it is found in the bloodstream of an egg laying duck. The virus is pass on from the infected duck to the egg resulting in congenital infection [3]. Ducks that are infected in utero are susceptible to developing hematomas or secondary amyloidosis. Since DHBV shares the same family as the contagious human form of the Hepatitis B virus, it is used for study as a safe alternative [4]. Hepadnaviruses can cause both acute and chronic liver diseases in ducks [5].
Duck hepatitis virus type 1 is classified as an enterovirus, DHV-2 is an astrovirus, and DHV-3 as a picornavirus. DHV-1 has the most significant effect on the economy due to its high mortality rate when the spread is not controlled on all duck-growing farms. The virion of DHV-1 is a 20-40 nm diameter, non-enveloped, icosahedral particle that is resistant to ether and chloroform as well as possesses the ability to survive under normal environmental conditions for an extended amount of time [6].
Clinical signs include sudden death, opisthotonus, paresis, paralysis and enophthalmos. DHV-1 infection is most virulent, with death occurring within 1–2 hours of clinical signs.
A preliminary diagnosis may be made based on the clinical signs and post-mortem examination. Autopsy should show an enlarged liver, which appears greenish and displays distinct ecchymotic haemorrhages. Inoculation, and direct immunofluorescence can be used to definitively diagnose DHV-1.
No treatment is effective once infected.
To prevent the disease, vaccination (ATCvet code QI01) is commercially available against DHV-1 and immunisation involves two or three inoculations. Additionally, DHV-1 can be prevented by strict isolation in the first 4–5 weeks of life. 5% phenol and formaldehyde can be used to inactivate the viruses in the environment.