Duck hepatitis virus
Encyclopedia
Introduction
Duck hepatitis is caused by the enteroviruses DHV-1 and DHV-3. It is a fatal disease of ducklings causing opisthotonusOpisthotonus
Opisthotonus or opisthotonos, from Greek roots, opistho meaning "behind" and tonos meaning "tension", is a state of a severe hyperextension and spasticity in which an individual's head, neck and spinal column enter into a complete "bridging" or "arching" position...
and hepatitis
Hepatitis
Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...
. 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
Virulence
Virulence is by MeSH definition the degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenicity of an organism - its ability to cause disease - is determined by its...
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
Picornavirus
A picornavirus is a virus belonging to the family Picornaviridae. Picornaviruses are non-enveloped, positive-stranded RNA viruses with an icosahedral capsid. The genome RNA is unusual because it has a protein on the 5' end that is used as a primer for transcription by RNA polymerase...
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 .
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 .
Duck Hepatitis is a Class B disease listed by the Office des International Epizooties. The disease is not considered a zoonosis
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...
.
Duck hepatitis B virus, or DHBV, is a part of the Hepadnaviridae
Hepadnaviridae
Hepadnaviruses are a family of viruses which can cause liver infections in humans and animals. There are two recognized genera:*Genus Orthohepadnavirus; type species: Hepatitis B virus...
family that also comprises human Hepatitis B virus
Hepatitis B virus
Hepatitis B is an infectious illness caused by hepatitis B virus which infects the liver of hominoidea, including humans, and causes an inflammation called hepatitis. Originally known as "serum hepatitis", the disease has caused epidemics in parts of Asia and Africa, and it is endemic in China...
and Woodchuck hepatitis virus
Woodchuck hepatitis virus
The Woodchuck hepatitis virus is a species of the genus Orthohepadnavirus. It is not a deadly 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 . 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 . Hepadnaviruses can cause both acute and chronic liver diseases in ducks .
Classifications
Duck hepatitis virus type 1 is classified as an enterovirusEnterovirus
Enteroviruses are a genus of ssRNA viruses associated with several human and mammalian diseases. Serologic studies have distinguished 66 human enterovirus serotypes on the basis of antibody neutralization tests. Additional antigenic variants have been defined within several of the serotypes on the...
, DHV-2 is an astrovirus
Astrovirus
Astrovirus is a type of virus that was first discovered in 1975 using electron microscopes following an outbreak of diarrhoea in humans. In addition to humans, astroviruses have now been isolated from numerous mammalian animal species and from avian species such as ducks, chickens, and turkey...
, and DHV-3 as a picornavirus
Picornavirus
A picornavirus is a virus belonging to the family Picornaviridae. Picornaviruses are non-enveloped, positive-stranded RNA viruses with an icosahedral capsid. The genome RNA is unusual because it has a protein on the 5' end that is used as a primer for transcription by RNA polymerase...
. 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 .
Clinical Signs & Diagnosis
Clinical signs include sudden death, opisthotonusOpisthotonus
Opisthotonus or opisthotonos, from Greek roots, opistho meaning "behind" and tonos meaning "tension", is a state of a severe hyperextension and spasticity in which an individual's head, neck and spinal column enter into a complete "bridging" or "arching" position...
, paresis
Paresis
Paresis is a condition typified by partial loss of voluntary movement or by impaired movement. When used without qualifiers, it usually refers to the limbs, but it also can be used to describe the muscles of the eyes , the stomach , and also the vocal cords...
, paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
and enophthalmos
Enophthalmos
Enophthalmos is the recession of the eyeball within the orbit.It may be a congenital anomaly, or be acquired as a result of trauma , Horner's syndrome, silent sinus syndrome, or phthisis bulbi....
. 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
An autopsy—also known as a post-mortem examination, necropsy , autopsia cadaverum, or obduction—is a highly specialized surgical procedure that consists of a thorough examination of a corpse to determine the cause and manner of death and to evaluate any disease or injury that may be present...
. Autopsy
Autopsy
An autopsy—also known as a post-mortem examination, necropsy , autopsia cadaverum, or obduction—is a highly specialized surgical procedure that consists of a thorough examination of a corpse to determine the cause and manner of death and to evaluate any disease or injury that may be present...
should show an enlarged liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, which appears greenish and displays distinct ecchymotic haemorrhages
Ecchymosis
An ecchymosis is the medical term for a subcutaneous purpura larger than 1 centimeter or a hematoma, commonly called a bruise. It can be located in the skin or in a mucous membrane.-Presentation:...
. Inoculation, and direct immunofluorescence
Immunofluorescence
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...
can be used to definitively diagnose DHV-1.
Treatment & Control
No treatment is effective once infected.To prevent the disease, vaccination
Vaccination
Vaccination is the administration of antigenic material to stimulate the immune system of an individual to develop adaptive immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens...
(ATCvet code QI01
ATCvet code QI01
-QI01AA Inactivated viral vaccines:-QI01AA Inactivated viral vaccines:-QI01AA Inactivated viral vaccines::QI01AA01 Avian infectious bursal disease virus:QI01AA02 Newcastle disease virus/paramyxovirus:QI01AA03 Avian infectious bronchitis virus...
) 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
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
and formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
can be used to inactivate the viruses in the environment.