duck virus hepatitis
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Top of pagePreferred Scientific Name
- duck virus hepatitis
International Common Names
- English: duck hepatitis
English acronym
- DH
- DVH
Overview
Top of pageDuck hepatitis (DH) is a complex disease syndrome caused by several viruses including duck hepatitis A virus (subtypes 1, 2 and 3, i.e. DHAV-1, -2 and -3), duck hepatitis B virus (DHBV) and duck hepatitis virus types 2 and 3. DH is a severe infection of ducklings, characterized by rapid onset of high mortality, opisthotonos and hepatitis. The potential for high morbidity and mortality make DH an economically important disease in all duck-growing areas.
Genome sequencing studies have revealed a great deal about these viruses (Kim et al., 2006; 2007a; Tseng et al., 2007; Fu et al., 2009; Todd et al., 2009; Yun et al., 2010; Wei et al., 2012), including that type 3 is not a picornavirus, as once thought, but an astrovirus, now called duck astrovirus 2 (DAstV-2) (Todd et al., 2009). Type 2 is also an astrovirus (subsequently renamed as duck astrovirus 1 (DAstV-1) (Todd et al., 2009), and type 1 is a picornavirus. DHV 1, the most common of the three viruses, with international distribution, is also known as duck hepatitis A virus (DHAV) in the new genus Avihepatovirus.
DHAV is a picornavirus, which causes a highly contagious infection with up to 100% mortality in ducklings under 6 weeks of age, while older ducks are unaffected. Duck hepatitis virus types 2 and 3 are astroviruses with phylogenetical similarity to turkey astroviruses. Duck astrovirus (DAstV) causes acute and often fatal infections in ducklings with clinical and pathological signs that are indistinguishable from DHAV (Yugo et al., 2016).
An avian disease caused by astroviruses was first reported in ducklings in 1965 (Asplin, 1965), but the virus was only recognized as an astrovirus in the mid-1980s using electron microscopy (Gough et al., 1984) and was initially termed duck hepatitis virus 2 (DHV-2) and later renamed duck astrovirus serotype 1 (DAstV-1) in more recent literature (Gough et al., 1985). Another astrovirus, originally termed DHV-3, which also causes hepatitis in ducklings (Haider and Calnek, 1979), is now known as DAstV-2 and is genetically and antigenically distinct from DAstV-1 (Todd et al., 2009).
DHVB infections caused by a member of the hepadnavirus group (hepatitis B viruses) are found in wild and domestic ducks, but these infections do not lead to the development of clinical signs or chronic infection.
Host Animals
Top of pageAnimal name | Context | Life stage | System |
---|---|---|---|
Anas (ducks) | |||
Anas platyrhynchos | Experimental settings | Poultry|Young poultry | |
Anser (geese) | Experimental settings | Poultry|Young poultry | |
Cairina (Muscovy ducks) | |||
Coturnix | Experimental settings | Poultry|Young poultry | |
Meleagris gallopavo (turkey) | Experimental settings | Poultry|Young poultry | |
Muscovy duck | Domesticated host | Poultry|Young poultry | |
Numida | Experimental settings | Poultry|Young poultry | |
Pekin duck | Domesticated host | Poultry|Young poultry | |
Phasianus (pheasants) | Experimental settings | Poultry|Young poultry |
Distribution
Top of pageDuck hepatitis A virus (DHAV) was first described in young white pekin ducks on Long Island, New York (Levine and Hofstad, 1945; Levine and Fabricant, 1950). Since then, DHAV has been reported in duck-raising areas worldwide (Woolcock, 2008), and DHAV outbreaks are frequent in China (Guo and Pan, 1984) and Korea (Park, 1985; Sung and Kim, 2000). DHAV-1 is the most common and virulent subtype with global distribution causing more than 80% mortality in ducklings.
DHAV type 2 (DAstV-1) was originally reported in Norfolk, England (Asplin, 1965). A duck astrovirus with very high sequence similarity to DAstV-1 (Todd et al., 2009) has been detected and sequenced in China (Fu et al., 2009), associated with very high mortality in one- to two-week-old commercial ducklings.
DHAV type 3 (DAstV-2) has first occurred in the USA, but is now prevalent in China, South Korea and Vietnam, and has recently been reported in 15 duckling flocks in the Sharkia province of Egypt (Hassan et al., 2020).
For current information on disease incidence, see OIE's World Animal Health Information System (OIE-WAHIS).
Distribution Table
Top of pageThe distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
Last updated: 14 Dec 2021Continent/Country/Region | Distribution | Last Reported | Origin | First Reported | Invasive | Reference | Notes |
---|---|---|---|---|---|---|---|
Africa |
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Algeria | Absent | Jul-Dec-2019 | |||||
Botswana | Absent | Jul-Dec-2018 | |||||
Burkina Faso | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Burundi | Absent | Jul-Dec-2018 | |||||
Cabo Verde | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Central African Republic | Absent | Jul-Dec-2019 | |||||
Congo, Democratic Republic of the | Absent | Jul-Dec-2019 | |||||
Côte d'Ivoire | Absent, No presence record(s) | ||||||
Djibouti | Absent | Jul-Dec-2019 | |||||
Egypt | Present, Localized | ||||||
Eswatini | Absent | Jul-Dec-2019 | |||||
Gabon | Absent, No presence record(s) | ||||||
Kenya | Absent | Jul-Dec-2019 | |||||
Lesotho | Absent | Jan-Jun-2020 | |||||
Liberia | Absent | Jul-Dec-2018 | |||||
Libya | Absent | Jul-Dec-2019 | |||||
Madagascar | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Malawi | Absent | Jul-Dec-2018 | |||||
Mauritius | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Mayotte | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Mozambique | Present | Jul-Dec-2019 | |||||
Namibia | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Nigeria | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Réunion | Absent | Jul-Dec-2019 | |||||
Rwanda | Absent | Jul-Dec-2018 | |||||
Saint Helena | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Seychelles | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Somalia | Absent | Jul-Dec-2020 | |||||
South Africa | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Sudan | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Togo | Absent | Jul-Dec-2019 | |||||
Tunisia | Absent | Jul-Dec-2019 | |||||
Asia |
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Afghanistan | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Armenia | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Azerbaijan | Absent | Jul-Dec-2019 | |||||
Bahrain | Absent, No presence record(s) | Jul-Dec-2020 | |||||
Bangladesh | Absent | Jan-Jun-2020 | |||||
Bhutan | Absent, No presence record(s) | Jan-Jun-2020 | |||||
Brunei | Absent | Jul-Dec-2019 | |||||
Cambodia | Absent | Jul-Dec-2019 | |||||
China | Present, Localized | Jul-Dec-2018 | |||||
Georgia | Absent, No presence record(s) | Jul-Dec-2019 | |||||
India | Absent | Jan-Jun-2019 | |||||
Indonesia | Absent | Jul-Dec-2019 | |||||
Iran | Absent | Jan-Jun-2019 | |||||
Iraq | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Israel | Absent | Jul-Dec-2020 | |||||
Japan | Absent | Jan-Jun-2020 | |||||
Jordan | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Kazakhstan | Absent | Jul-Dec-2019 | |||||
Kuwait | Absent | Jan-Jun-2019 | |||||
Kyrgyzstan | Absent | Jan-Jun-2019 | |||||
Laos | Absent | Jan-Jun-2019 | |||||
Lebanon | Absent | Jul-Dec-2019 | |||||
Malaysia | Absent | Jan-Jun-2019 | |||||
-Peninsular Malaysia | Absent, No presence record(s) | ||||||
Maldives | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Mongolia | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Myanmar | Absent | Jul-Dec-2019 | |||||
Nepal | Absent, No presence record(s) | Jul-Dec-2019 | |||||
North Korea | Absent, No presence record(s) | ||||||
Oman | Absent | Jul-Dec-2019 | |||||
Pakistan | Absent | Jan-Jun-2020 | |||||
Palestine | Absent | Jul-Dec-2019 | |||||
Qatar | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Saudi Arabia | Absent, No presence record(s) | Jan-Jun-2020 | |||||
Singapore | Absent | Jul-Dec-2019 | |||||
South Korea | Present, Localized | Jul-Dec-2019 | |||||
Sri Lanka | Absent | Jul-Dec-2018 | |||||
Syria | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Taiwan | Absent | Jul-Dec-2019 | |||||
Tajikistan | Absent | Jan-Jun-2019 | |||||
Thailand | Absent | Jan-Jun-2020 | |||||
Turkmenistan | Absent | Jan-Jun-2019 | |||||
United Arab Emirates | Absent | Jul-Dec-2020 | |||||
Uzbekistan | Absent | Jul-Dec-2019 | |||||
Vietnam | Present | Jul-Dec-2019 | |||||
Europe |
|||||||
Andorra | Absent | Jul-Dec-2019 | |||||
Belarus | Absent | Jul-Dec-2019 | |||||
Belgium | Absent | Jul-Dec-2019 | |||||
Bosnia and Herzegovina | Absent | Jul-Dec-2019 | |||||
Bulgaria | Absent | Jan-Jun-2019 | |||||
Croatia | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Cyprus | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Czechia | Absent | Jul-Dec-2019 | |||||
Denmark | Absent, Unconfirmed presence record(s) | ||||||
Estonia | Absent | Jul-Dec-2019 | |||||
Faroe Islands | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Finland | Absent, No presence record(s) | Jul-Dec-2019 | |||||
France | Absent | Jul-Dec-2019 | |||||
Germany | Absent | Jul-Dec-2019 | |||||
Greece | Absent | Jan-Jun-2018 | |||||
Hungary | Absent | Jul-Dec-2019 | |||||
Iceland | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Ireland | Absent, No presence record(s) | ||||||
Italy | Absent | Jul-Dec-2020 | |||||
Latvia | Absent | Jul-Dec-2020 | |||||
Liechtenstein | Absent | Jul-Dec-2019 | |||||
Lithuania | Absent | Jul-Dec-2019 | |||||
Luxembourg | Absent, No presence record(s) | ||||||
Malta | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Moldova | Absent | Jan-Jun-2020 | |||||
Montenegro | Absent | Jul-Dec-2019 | |||||
Netherlands | Absent | Jul-Dec-2019 | |||||
North Macedonia | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Norway | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Portugal | Absent | Jul-Dec-2019 | |||||
Romania | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Russia | Absent | Jan-Jun-2020 | |||||
San Marino | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Serbia | Absent | Jul-Dec-2019 | |||||
Serbia and Montenegro | Absent, No presence record(s) | ||||||
Slovakia | Absent | Jul-Dec-2020 | |||||
Slovenia | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Spain | Absent | Jul-Dec-2020 | |||||
Sweden | Absent, No presence record(s) | Jul-Dec-2020 | |||||
Switzerland | Absent | Jul-Dec-2020 | |||||
Ukraine | Absent | Jul-Dec-2020 | |||||
United Kingdom | Absent | Jul-Dec-2019 | |||||
-Northern Ireland | Absent, No presence record(s) | ||||||
North America |
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Bahamas | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Barbados | Absent, No presence record(s) | Jul-Dec-2020 | |||||
Belize | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Bermuda | Absent, No presence record(s) | ||||||
British Virgin Islands | Absent, No presence record(s) | ||||||
Canada | Absent | Jul-Dec-2019 | |||||
Cayman Islands | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Costa Rica | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Cuba | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Curaçao | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Dominica | Absent, No presence record(s) | ||||||
Dominican Republic | Absent, No presence record(s) | Jan-Jun-2019 | |||||
El Salvador | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Greenland | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Guatemala | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Haiti | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Honduras | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Jamaica | Absent | Jul-Dec-2018 | |||||
Mexico | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Nicaragua | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Saint Kitts and Nevis | Absent, No presence record(s) | ||||||
Saint Lucia | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Saint Vincent and the Grenadines | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Trinidad and Tobago | Absent, No presence record(s) | Jan-Jun-2018 | |||||
United States | Absent | Jul-Dec-2019 | |||||
Oceania |
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Australia | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Cook Islands | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Federated States of Micronesia | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Fiji | Absent, No presence record(s) | Jan-Jun-2019 | |||||
French Polynesia | Absent | Jan-Jun-2019 | |||||
Kiribati | Absent, No presence record(s) | Jan-Jun-2018 | |||||
Marshall Islands | Absent, No presence record(s) | Jan-Jun-2019 | |||||
New Caledonia | Absent | Jul-Dec-2019 | |||||
New Zealand | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Palau | Absent, No presence record(s) | Jul-Dec-2020 | |||||
Samoa | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Timor-Leste | Absent, No presence record(s) | Jul-Dec-2018 | |||||
Tonga | Absent | Jul-Dec-2019 | |||||
Vanuatu | Absent, No presence record(s) | Jan-Jun-2019 | |||||
South America |
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Argentina | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Brazil | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Chile | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Colombia | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Ecuador | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Falkland Islands | Absent, No presence record(s) | Jul-Dec-2019 | |||||
French Guiana | Absent | Jul-Dec-2019 | |||||
Guyana | Present | Jul-Dec-2020 | |||||
Paraguay | Absent | Jul-Dec-2019 | |||||
Peru | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Suriname | Absent, No presence record(s) | Jan-Jun-2019 | |||||
Uruguay | Absent, No presence record(s) | Jul-Dec-2019 | |||||
Venezuela | Absent, No presence record(s) | Jan-Jun-2019 |
Pathology
Top of pageGross lesions are predominately found in the liver, which is enlarged and displays distinct punctuate or ecchymotic haemorrhages. Spleen enlargement and swelling of the kidneys, with congestion of renal blood vessels is also observed. Occasionally, small haemorrhages are seen in the intestinal wall and on the heart fat with DAstV-1 infection. Gross pathological changes with DAstV-2 are similar to those caused by DHAV.
Histopathological changes in DHAV infection consist of necrosis of hepatic cells and varying degrees of inflammatory cell infiltration. In survivors, more chronic lesions showed regeneration of liver parenchyma and widespread bile duct hyperplasia. All microscopic changes associated with DHAV infections were analysed in experimentally induced DHAV infection (Fabricant et al., 1957). Peng showed by electron microscopy that DHAV invades many tissues in the duckling and causes swelling, haemorrhage and necrosis of the liver, spleen, kidneys and pancreas. Pathological changes are also seen in the central nervous system and the bursa of Fabricii in infected ducklings (Peng, 1998). Lesions are similar with DAstV-1 and DAstV-2 infection.
Diagnosis
Top of pageThere are several approaches for the diagnosis of DH, which involve examining clinical signs and gross pathological changes, or reproducing the disease in susceptible ducklings. However, these techniques are incapable of discriminating DHAV-1 and DHAV-3 because of their similar clinical signs and gross pathological lesions (Liu et al., 2011). Virus isolation combined with polymerase chain reaction (PCR) (Saha et al., 2013), immunofluorescence assays (Zhang et al., 2014; Wu et al., 2015), neutralization test (Hwang, 1969) or enzyme-linked immunosorbent assays (ELISA) (Shen et al., 2015) are reliable for detecting DHAV, but these techniques are all labour-intensive and time-consuming.
DHV type I (DHAV)
The clinical and pathological observations are highly indicative of a DHAV infection. Preparing 20% (w/v) liver homogenate suspensions, from birds that are thought to have had the infection, in buffered saline and inoculating the allantoic sac of eight- to ten-day-old chicken embryos can isolate the virus. Infected embryos will die within 5 to 8 days post-infection and exhibit gross lesions, including dwarfing, enlarged greenish livers with necrotic foci and cutaneous haemorrhage and oedema. Embryo mortality and lesions will occur sooner after inoculation, in 10- to 14-day-old duck embryos from susceptible breeder ducks. The presence of DHAV can be confirmed by one of more of the following tests:
a. Subcutaneous or intramuscular inoculation of the isolate into one- to seven-day-old susceptible ducklings results in death 18 to 48 h post-infection. Gross lesions should be consistent with DHAV infection and the virus should be re-isolated from the livers.
b. Inoculation of serial dilutions of the liver homogenate into the allantoic sac of duck or chicken eggs and observation of clinical changes as described above.
c. Inoculation of liver homogenate suspensions into primary cultures of duck embryo liver cells. DHAV will cause a cytopathic effect (CPE) in the cells. Recently, an attenuated strain of DHAV was reported to replicate in chicken embryo fibroblasts (Zhang et al., 2000). A duck embryo fibroblast cell line has been developed, in which DHAV replicates with cytopathic effect (Fu et al., 2012).
d. An accurate diagnosis of DHAV can be made using direct immunofluorescence on livers from naturally occurring infections or inoculated duck embryos (Vertinskii et al., 1968; Maiboroda, 1972).
e. An ELISA for antibodies to DHAV has been developed using virus protein 1 (VP1) produced in bacteria as antigen (Liu et al., 2010).
f. Reverse transcriptase polymerase chain reaction (RT-PCR) tests have been developed for DHAV (Kim et al., 2007b; 2008; Cheng et al., 2009) and reverse transcription loop-mediated isothermal amplification tests by Song et al. (2012) and Yang et al. (2012), but these tests are labour-intensive and expensive. A rapid and economical one-tube RT-PCR technique for simultaneous detection and genotyping of duck hepatitis A virus subtypes 1 and 3 has been developed recently using a universal primer and type-specific primers targeted to the 5’-NCR sequence (Chen et al., 2019).
DHV type II (DAstV-1)
The virus may be recovered in a 20% (w/v) homogenized liver suspension and can be used to inoculate susceptible ducklings and embryonated chicken eggs. An outbreak of DAstV-1 in China in 2008 killed approximately 50% of one- to two-week-old commercial ducklings (Fu et al., 2009). As sequence data is now available for DAstV-1, RT-PCRs can be used to detect the virus (Fu et al., 2009; Todd et al., 2009).
Gross lesions will be similar to field cases. Chicken eggs can also be inoculated, either by the amniotic cavity or the yolk sac. This results in very little mortality and stunted green necrotic livers are the only observable pathology. There are no cell culture systems for DAstV-1.
DHV type III (DAstV-2)
The virus can be recovered from homogenized liver suspensions and isolated by duckling inoculation, or inoculation onto the chorioallantoic membrane of ten-day-old embryonated duck eggs. There will be some embryo mortality 7 to 10 days post-inoculation and the membrane will appear dry and crusty. DAstV-2 is less virulent than DHAV.
Serologic tests
Serologic tests have not been useful because of the acute nature of the clinical disease. However, various virus neutralization (VN) assays have been described that are useful for virus identification, titration of serologic response to vaccination and epidemiologic surveys. The VN tests may achieve greater significance if DAstV-1 and DAstV-2 become more widespread. The VN tests described include a DHAV neutralization test in chicken embryos (Hwang, 1969), an agar gel diffusion precipitin (AGDP) test for identification of type I (Murty and Hanson, 1961) and a plaque-reduction test for VN antibodies (Woolcock et al., 1982). A duck embryo fibroblast cell line has been developed, in which DHAV replicates with cytopathic effect (Fu et al., 2012).
Differential Diagnosis
Although the sudden onset, rapid spread and acute course of the disease are characteristic of DHAV, the virus must be isolated or demonstrated by RT-PCR to confirm DHAV infection. Other potential causes of acute mortality in ducklings include salmonella and aflatoxin. Neither of these causes the liver lesions characteristic of DHAV infection, but will produce rapid onset mortality and ataxia, convulsions and opisthotonos in the case of aflatoxicosis.
List of Symptoms/Signs
Top of pageSign | Life Stages | Type |
---|---|---|
Digestive Signs / Hepatosplenomegaly, splenomegaly, hepatomegaly | Poultry|Young poultry | Sign |
General Signs / Ataxia, incoordination, staggering, falling | Poultry|Young poultry | Sign |
General Signs / Haemorrhage of any body part or clotting failure, bleeding | Poultry|Young poultry | Sign |
General Signs / Increased mortality in flocks of birds | Poultry|Young poultry | Sign |
General Signs / Opisthotonus | Poultry|Young poultry | Sign |
General Signs / Sudden death, found dead | Poultry|Young poultry | Sign |
General Signs / Weakness, paresis, paralysis of the legs, limbs in birds | Poultry|Young poultry | Sign |
Musculoskeletal Signs / Spasms of the limbs, legs, foot, feet in birds | Poultry|Young poultry | Sign |
Ophthalmology Signs / Enophthalmos, sunken eyes | Poultry|Young poultry | Sign |
Disease Course
Top of pageDHAV causes a highly contagious, often fatal infection of ducklings, especially in those under 6 weeks of age. The onset and spread of DHAV is very rapid and is initially characterized by lethargy and ataxia. Within a short time, ducklings stop moving and squat with their eyes partially closed, this is followed by loss of balance, spasmodic kicking of both legs and death. At death, the head is usually drawn back in the opisthotonos position. Death occurs very rapidly, often within 1 to 2 h after the onset of clinical signs. Morbidity is 100% and mortality is variable depending on the age at infection. DAstV-1 and DAstV-2 cause similar clinical signs and disease course as DHAV. An outbreak of DAstV-1 in China in 2008 killed approximately 50% of one- to two-week-old commercial ducklings (Fu et al., 2009).
Epidemiology
Top of pageDHV type I (DHAV)
In naturally occurring outbreaks, DHAV occurs only in young ducks. Experimentally, infection of goslings, mallard ducklings, turkey poults, quail, young pheasants, geese and guinea fowl with DHAV have been reported (Hwang, 1974; Woolcock, 2008). DHAV will rapidly spread to all susceptible ducklings in a flock. Recovered ducks may excrete the virus in their faeces and the virus remains viable in the faeces for many weeks. It is probable that infection follows the ingestion by susceptible ducklings of virus-carrying particles from the environment. Variants of DHAV have been described in South Korea (Kim et al., 2007a; 2008). There is no evidence of egg transmission. There are reports suggesting that wild birds (Asplin, 1961) or brown rats (Demakov et al., 1975) may serve as mechanical vectors or host reservoirs for DHAV.
DHV type II (DAstV-1)
Only ducks appear to be affected by DAstV-1. The earliest described outbreaks occurred in ducks kept on open fields in eastern England, initially reported in 1965 and up to 1969, then again in 1983/1984, which were the last reported outbreaks in England. However, the role of wildfowl, wild birds and wildlife reservoirs or vectors is unknown (Gough, 1986; Woolcock, 2008). In 2008, there was a severe outbreak of duck hepatitis in China. Virus present in liver extracts had very high amino acid sequence identity (Fu et al., 2009) to the DAstV-1 sequenced by Todd et al. (2009) and very different to DAstV-2 (Todd et al., 2009).
DHV type III (DAstV-2)
There is little known about the epidemiology of DAstV-2, which has only been described in the USA (Woolcock, 2008).
Impact: Economic
Top of pageDuck hepatitis is recognized as an economically important disease in all duck-growing areas because of the potential for high morbidity and mortality if not controlled.
Disease Treatment
Top of pageAqueous extract of Le-Cao-Shi (LCS), a traditional Chinese medicine formula, has shown promising results for the treatment of hepatitis B in recent in vivo and in vitro experiments using a duck hepatitis B model (Zhao et al., 2019).
Prevention and Control
Top of pageHusbandry Methods and Good Practice
DHAV can be prevented by strict isolation during the first 4 to 5 weeks of life. In areas where the disease is prevalent, achieving the necessary degree of isolation may be very difficult and vaccination may be required.
Immunization and Vaccines
DHV type I (DHAV)
Resistance against DHAV in ducklings can be achieved through three methods:
1. Injection of immune serum or yolk from eggs produced by hyperimmune breeder ducks, or yolk from eggs produced by specific-pathogen-free chickens hyperimmunized with DHAV.
2. Immunization of breeder stocks with a live attenuated virus vaccine. The vaccine is produced in embryonated chicken eggs to ensure high levels of passively transferred antibodies in ducklings. Alternatively, breeder ducks can also be vaccinated with an inactivated vaccine if they have already been primed with, or exposed to, live DHAV.
3. Direct immunization of ducklings with live avirulent strains of DHAV by foot web-stab, intramuscular, intranasal or subcutaneous injection. DHAV-1 vaccines may not be fully effective against type 2 and 3 DHAV. Kim et al. (2009) have produced an attenuated DHAV-3 vaccine using a strain that had been circulating in South Korea and China, but there is no vaccine which is licenced for use in China. Another live vaccine candidate against DHAV-3 has been developed in China (Wu et al., 2020) using an attenuated field isolate strain (SD70). The minimum effective dose of SD70 after subcutaneous inoculation was 102.5ELD50. A single dose of the SD70 provided good protection to susceptible ducklings against DHAV-3 strain without causing any clinical signs of disease or mortality in one-day-old ducklings and there was no virulence reversion. The attenuated SD70 strain exhibited good safety, stability and protection, and is a promising vaccine candidate for the prevention of DHAV-3 infection.
DHV type II (DAstV-1)
A live virus, DAstV-1 vaccine, protected ducklings under experimental conditions but has never been used commercially.
DHV type III (DAstV-2)
Experimentally, an attenuated live-virus vaccine given to breeder ducks confers immunity to hatchling ducklings. Also, convalescent sera obtained from DAstV-2-infected ducks effectively controlled outbreaks in the field.
National and International Control Policy
As defined by the OIE the incubation period for DVH is 7 days. The Veterinary Administrations of importing countries should require the presentation of an international veterinary certificate attesting that:
- The ducks showed no clinical signs of DVH on the day of shipment.
- The ducks come from establishments that are free from DVH.
- That the ducks are either vaccinated or not vaccinated against DVH.
There are further requirements for the importation of day-old ducks and duck embryonated eggs.
References
Top of pageOffice International des Epizooties, 1999. World animal health in 1999. Paris, France: OIE.
Distribution References
CABI, Undated. Compendium record. Wallingford, UK: CABI
CABI, Undated a. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI
OIE Handistatus, 2005. World Animal Health Publication and Handistatus II (dataset for 2004)., Paris, France: Office International des Epizooties.
OIE, 2009. World Animal Health Information Database - Version: 1.4., Paris, France: World Organisation for Animal Health. https://www.oie.int/
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