以下是我文章的摘要部分请为我凝练出4点Highlights。Koi herpesvirus KHV poses a significant threat to the koi and common carp aquaculture industry due to its high mortality rate among infected fish In this study we success

Highlights:

1. The deletion of open reading frames 56 and 57 (ORF56-57) in the Asian KHV strain SS09 leads to attenuation of the virus.
2. Fish infected with the mutant strain SS09 Δ56-57 did not show mortality, while the mortality rate of fish infected with the wild strain was nearly 100%.
3. Immersion immunization of koi fish with SS09 Δ56-57 resulted in a relative percentage survival (RPS) ranging from 70.0% to 96.6%.
4. SS09 Δ56-57 exhibits outstanding immunogenicity, safety, and efficacy, making it a promising candidate vaccine strain for KHV disease.