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      Isolation and molecular characterization of prevalent Fowl adenovirus strains in southwestern China during 2015–2016 for the development of a control strategy

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          Abstract

          Fowl adenovirus (FAdV) has caused significant losses in chicken flocks throughout China in recent years. However, the current understanding of the genetic and pathogenic characteristics of the FAdV epidemic in southwestern China remains poorly understood. In this study, a total of 22 strains were isolated from liver samples of diseased chickens from farms in southwestern China. Phylogenetic analysis based on the hexon loop-1 gene showed that the 22 isolates were clustered into four distinct serotypes: FAdV serotype 4 (FAdV-4) (86.4%, 19/22), FAdV-2 (4.5%, 1/22), FAdV-8a (4.5%, 1/22), and FAdV-8b (4.5%, 1/22). FAdV-4 was the predominant serotype in southwestern China. Pathogenicity testing showed that the FAdV-4 serotype strain CH/GZXF/1602 and FAdV-8a strain CH/CQBS/1504 were pathogenic to chickens, with mortality rates reaching as high as 80% and 20%, respectively. The primary clinical feature observed following infection with strain CH/GZXF/1602 (FAdV-4) was hepatitis-hydropericardium syndrome, and that of strain CH/CQBS/1504 (FAdV-8a) was inclusion body hepatitis. Conversely, the FAdV-2 serotype strain CH/GZXF/1511 and FAdV-8b serotype strain CH/CQBS/1512 was not observed to be pathogenic in chickens. Then, CH/GZXF/1602 (FAdV-4) was selected for the preparation of an inactivated oil-emulsion vaccine. Immune studies on Partridge Shank broilers showed that a single dose immunization at 17 days of age could not only protect against homologous challenge with virulent FAdV-4 but also provided protection against clinical disease following challenge with the heterologous FAdV-8b virulent strain until 70 days of age. The characterization of newly prevalent FAdV strains provides a valuable reference for the development of an efficacious control strategy.

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          Most cited references46

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          Adenoviruses: update on structure and function.

          Adenoviruses have been studied intensively for over 50 years as models of virus-cell interactions and latterly as gene vectors. With the advent of more sophisticated structural analysis techniques the disposition of most of the 13 structural proteins have been defined to a reasonable level. This review seeks to describe the functional properties of these proteins and shows that they all have a part to play in deciding the outcome of an infection and act at every level of the virus's path through the host cell. They are primarily involved in the induction of the different arms of the immune system and a better understanding of their overall properties should lead to more effective ways of combating virus infections.
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            Detection and differentiation of avian adenoviruses: a review.

            M. Hess (2000)
            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.
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              Polymerase chain reaction combined with restriction enzyme analysis for detection and differentiation of fowl adenoviruses.

              A polymerase chain reaction combined with restriction enzyme analysis was developed for detection and differentiation of all 12 fowl adenovirus (FAdV) serotypes representing the five fowl adenovirus (A to E) species. For primer design, the published sequences of the hexon proteins of FAdV1, FAdV8 and FAdV9 were aligned and conserved regions in the two pedestal regions adjacent to the L1 loop region were determined. A primer pair (hexon A/hexon B) was constructed and was shown to amplify approximately 900 bp of the hexon gene including the L1 loop region. An amplification product was detected using supernatant of infected cell cultures from all FAdV1 to FAdV12 reference strains used in our study. The sequence and the restriction patterns of the hexon A/B fragments of the 12 FAdV strains were determined and compared. The successive use of four different endonucleases allowed the complete differentiation of the reference FAdV strains. Twenty-six fowl adenoviruses isolated during our routine virological diagnosis activities could all be amplified using hexon A/hexon B primers. Restriction analysis results showed that 8/26 adenovirus strains contained two different FAdV types. FAdV4, FAdV12, FAdV1, FAdV5 and FAdV6 were the most frequently isolated.
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                Author and article information

                Journal
                Emerg Microbes Infect
                Emerg Microbes Infect
                Emerging Microbes & Infections
                Nature Publishing Group
                2222-1751
                November 2017
                29 November 2017
                1 November 2017
                : 6
                : 11
                : e103
                Affiliations
                [1 ]College of Veterinary Medicine, Sichuan Agricultural University , Chengdu, Sichuan 611130, China
                Author notes
                [✝]

                These authors contributed equally to this work.

                Article
                emi201791
                10.1038/emi.2017.91
                5717092
                29184155
                43f58a1a-00d2-4811-acba-060d5d1d387f
                Copyright © 2017 The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 05 June 2017
                : 04 September 2017
                : 17 September 2017
                Categories
                Original Article

                epidemiology,fadv serotype 4,fadv serotype 8a,fowl adenovirus,pathogenic,vaccine

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