Detection and differentiation of avian adenoviruses: A review

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Abstract
Avian adenoviruses are a very diverse group of pathogens causing a variety of problems for poultry production. For a long time, the diagnosis of an adenovirus infection was restricted to the isolation of the respective virus followed by various serological typing methods, such as immunofluorescence assay, neutralization test or haemagglutination-inhibition test. In addition, restriction enzyme analysis has been reported for differentiation of avian adenoviruses. Besides summarizing the classical diagnostic methods, this review is mainly focused on the challenges that occurred recently in the field of avian adenovirus diagnosis at the molecular level. Several polymerase chain reactions (PCRs) have been published to diagnose all three groups of avian adenoviruses. Most PCRs were established to detect fowl adenovirus (FAV) DNA. Some of them were combined with restriction enzyme analysis to investigate whether FAV reference strains and field isolates could be typed according to the restriction profiles of the PCR products. The great advantage of direct detection of the viral DNA in tissue samples was demonstrated for the haemorrhagic enteritis virus and egg drop syndrome virus. Other PCRs were developed with the aim of detecting viral DNA from all three groups of avian adenoviruses partially in target cells. Whereas the value of these PCRs for avian adenovirus diagnostics is not disputable, the problems and open questions that are still present are also discussed.