Abstract
A hypervirulent fowl adenovirus serotype 4 (FAdV-4) has caused hepatitis-hydropericardium syndrome (HHS) with mortalities that range from 30 to 80% in outbreaks across China since 2015. The FAdV-4 strain was characterized as a novel genotype based on the specific genome characteristics. However, our understanding of the dynamic distribution, tissue tropism, and pathogenesis of the novel FAdV-4 is incomplete. In this study, a new, sensitive and FAdV-4-specific real-time PCR was developed and applied to detect the dynamic distribution of the duck origin, novel FAdV-4 strain HLJDAd15 in experimentally infected special-pathogen free (SPF) chickens and ducks. Notably, the pathogenicity and replication pattern of HLJDAd15 were completely different between chickens and ducks. Severe hydropericardium and 10% mortality were induced in chickens, whereas no clinical signs were observed in any duck. The virus replicated was detected throughout the study in both chickens and ducks. However, only one replication peak with a high virus concentration appeared in chickens at 5 days post infection (dpi), whereas two peaks with relatively low virus titres appeared in ducks at 7 and 21 dpi. Thus, ducks could be a natural reservoir of the novel FAdV-4 absent of clinical signs, and a new transmission route from ducks shedding FAdV-4 continually to chickens was revealed, which might aggravate the outbreak of HHS in chickens. This study provides the first accurate quantitative data for the replication kinetics of the novel FAdV-4 in different hosts. The different pathogenicity, dynamic distribution and replication pattern in chickens and ducks provide a foundation for further clarification of the pathogenesis of the novel FAdV-4.
Highlights
Adenoviruses, family Adenoviridae, are non-enveloped and double-stranded DNA viruses (Stewart et al, 1993)
To generate a standard curve for the real-time PCR, the standard recombinant plasmid pAD341 was serially diluted from 1 × 101 to 1 × 1011 copies/μl, and the serial-diluted plasmids were detected by the real-time PCR assay
Viral DNA from 11 chicken origin and 1 duck origin fowl adenovirus serotype 4 (FAdV-4) isolates was subjected to the established real-time PCR and was well detected, whereas fluorescent signals from viral DNA of FAdV-1, Marek’s disease virus (MDV), chicken infectious anaemia virus (CAV), and avian gyrovirus 2 (AGV2) and proviral DNA of reticuloendotheliosis virus (REV), ALV-A, ALV-B, and ALV-J were not detected, indicating the specificity of the real-time PCR for FAdV-4 (Figure 1B)
Summary
Adenoviruses, family Adenoviridae, are non-enveloped and double-stranded DNA viruses (Stewart et al, 1993). Members of the genus Aviadenovirus, are further separated into either five species (designated FAdV-A to FAdV-E) based largely on molecular criteria and restriction enzyme digest pattern or twelve serotypes (designated FAdV-1 to 8a and -8b to 11) based on the results of serum cross-neutralization tests (Hess, 2000). HHS appears with high frequency in chickens, in broilers, with a mortality that ranges from 10 to 100% (VeraHernández et al, 2016; Pan et al, in press). For diagnosis of FAdVs infection, several routine PCR methods have been reported based on serotype-specific hexon gene (Steer et al, 2009; Kaján et al, 2013) and a SYBR Green based real-time PCR within 52K gene was developed for detection and quantitation of all FAdV species (Günes et al, 2012). A sensitive serotype 4 specific quantitate PCR has not been available and urgently needed for diagnosis and deeper investigation of FAdV-4, especially the emerged novel FAdV-4
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