Atadenovirus (see Table 1).
Natural hosts of EDS virus were originally waterfowl, but historically, the virus was adapted to chickens by contaminated Marek’s vaccines produced in duck-embryo fibroblast cultures in the seventies (EDS 76).
Only certain serotypes have been associated with diseases in chickens. Within the genus Aviadenovirus 5 species (A to D) have been identified based on the molecular structure, and 12 serotypes based largely on cross-neutralization assays.
As there are major differences in nomenclature of FAdV strains between the US and Europe, the use of the ICTV (International Committee on Taxonomy of Viruses) classification is strongly recommended.
Antibody detection by serology and pathogen identification by virology and molecular biology are also essential tools for a correct diagnosis.
Various laboratory tests are available for detection of antibodies against FAdV.
They differ between those detecting antibodies against all serotype’s, like the group-specific Agar Gel Precipitation Test and ELISA’s, and the serotype-specific virus neutralization test (VN).
The Immunofluorescence test (IFT) can detect both antigen and antibodies.
Experimental and commercial ELISA test kits are frequently used for measuring FAdV antibody titers, however these tests can not differentiate antibodies against different FAdV serotypes.
The VN is an essential tool to identify the FAdV serotype in the field if virus isolates cannot be obtained. The VN test is also recommended for monitoring the sero- response after vaccination.
Pathogen identification by virus isolation in chick-embryo liver cells is limited to specific laboratories and uses the identification of Adeno specific cytopathic effects together with fluorescent antibody staining or subsequent PCR testing.
Nowadays molecular biological techniques are commonly used as they are less time consuming and do not require the use of tissue culture techniques. PCR testing followed by DNA sequencing or high-resolution melting (HRM-) curve analysis allows not only the detection but also subtyping of FAdV pathogens in the field.
Suitable samples are:
The strict Biosecurity protocols in breeder flocks during the rearing period might have a negative impact on prevention of Fowl Adenovirus infections: the more isolated the breeder flocks are kept in the rearing period, the more likelihood is an infection with FAdV during the production period, followed by vertical transmission of the virus in a period of 4-6 weeks after exposure until the breeders develop sufficient antibodies to prevent vertical transmission.
Whereas inactivated vaccines are available for the control of Egg Drop Syndrome, no commercially licensed vaccines are available for Fowl Adeno Viruses in most parts of the world.
The aim of vaccination is primarily the prevention of vertical transmission and the protection of day-old chicks by maternal antibodies.
Vaccination of breeder flocks twice in the rearing period at 10-12 and 16-18 weeks of age is recommended.
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