Different Dynamic Distribution in Chickens and Ducks of the Hypervirulent, Novel Genotype Fowl Adenovirus Serotype 4 Recently Emerged in China

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.

An Inactivated Novel Genotype Fowl Adenovirus 4 Protects Chickens against the Hydropericardium Syndrome That Recently Emerged in China

“…For vaccinated chickens, no obvious clinical signs and pathological damage were observed in chickens of both the single and double immunization groups, suggesting the safety and sufficient protection of the vaccine. As reported, the novel genotype FAdV-4 has specificities of continuous infection and cross-transmission between chickens and ducks [ 29 ]. This suggests that the infected chickens could continually contain and shed the virus to the environment for a long time.…”

“…Serum samples were obtained for antibody and cytokine assays at four time points: 7 and 14 days post the first and second immunization. Tissue samples, including the heart, liver, spleen, lung, kidney, thymus, and bursa, were collected 5 days post challenge for histopathology assay and virus quantification [ 29 ].…”

“…The relative TaqMan probe was a 23 bp oligonucleotide: 5′(FAM)-TCTGTCGTGACATTTCGGGTGGG-3′(TAMRA). The reactions were conducted with a predenaturation step at 95 °C for 5 min, an amplification at a melting temperature of 95 °C for 10 s, and an annealing/elongation at 65 °C for 40 s [ 29 , 31 ]. The fluorescent signal was collected during the elongation step.…”

“…A 341 bp fragment containing the probe sequence was cloned into a pEASY-T1 vector from 10 1 to 10 11 copies/μL, and were used to produce a standard curve. The final concentration was calculated in copy numbers in one mg tissue samples [ 29 ].…”

Identification of chicken CAR homology as a cellular receptor for the emerging highly pathogenic fowl adenovirus 4 via unique binding mechanism

“…The cells were washed 3 times with phosphate-buffered saline (PBS; pH 7.0) and then cultured at 37°C. The samples were collected at 24 hpi and the virus copy numbers were detected by qPCR [28].…”