Abstract
Egg drop syndrome virus (EDSV) can markedly decrease egg production in laying hens. Duck is the natural host of EDSV. EDSV derived from ducks abrogate egg drop in laying hens. We have previously confirmed that duck-derived EDSVs have a variety of replication activities in chick embryo liver (CEL) cells. However, it is currently unclear whether duck-derived EDSV could display tropism and adaptation in laying hens. This study assessed whether duck-derived EDSV can adapt to laying hens, and estimated the inducing factors. Complete genome sequences of duck-derived EDSVs (D11-JW-012, D11-JW-017, and D11-JW-032 isolates) with various replication efficiency in CEL cells and C10-GY-001 isolate causing disease in laying hens were analyzed to find their differences. Phylogenetic analysis of complete genome sequence revealed that C10-GY-001, D11-JW-032, and strain 127 virus as vaccine were clustered into the same group, with D11-JW-012 and D11-JW-017 clustered in another group. Comparison between D11-JW-012 isolate that poorly replicated and D11-JW-017 isolate that replicated well in CEL cells in same cluster revealed six amino acid differences on IVa2, DNA polymerase, endopeptidase, and DNA-binding protein. These amino acids might be key candidates enhancing cellular tropism in chicken. When the pathogenicities of these isolates in laying hens were compared, D11-JW-032 showed severe signs similar to 127 virus, D11-JW-017 showed intermediate signs, while D11-JW-012 showed almost no sign. Eleven amino acids differed between D11-JW-032 and D11-JW-017, and 17 amino acids were different between D11-JW-032 and D11-JW-012. These results suggest that EDSVs derived from ducks have various pathogenicities in laying hens. Key amino acid candidates might have altered their affinity to tropism of laying hens, causing difference pathogenicities.
Highlights
Egg drop syndrome virus (EDSV) can infect chickens, causing major economic losses due to its direct effect on egg production and eggshell quality
Genome sequences of Korean isolates of EDSV derived from laying chickens (C10-GY-001) and Pekin ducks (D11-JW-012, D11-JW-017, and D11-JW-032) were fully sequenced, Fig 1
The nucleotide sequences of these complete genomes were analyzed. These Korean isolates of EDSV shared 99.76–99.9% sequence similarities with published sequences of 127 and FJ12025 viruses isolated from chickens and Muscovy ducks, respectively
Summary
Egg drop syndrome virus (EDSV) can infect chickens, causing major economic losses due to its direct effect on egg production and eggshell quality. EDSV outbreak in laying chickens was first reported in 1976 [1]. EDSV isolated from healthy duck flock resulted in EDS signs in chickens similar to equal decrease in egg production produced by the 127 virus [11]. EDSV isolates D11-JW-017 obtained from Pekin ducks have high replication ability in CEL cells [12]. Their replication ability is similar to the C10-GY-001 outbreak strain isolated from laying hens. To improve our understanding of genetic diversity at genome level for EDSVs that reside in distinct hosts and gain insights into their evolutionary path, we performed comparative genomic and pathogenic analyses of EDSVs isolated from chickens and ducks in this study
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