Molecular detection and characterisation of herpesviruses in asymptomatic Russian sturgeon (Acipenser gueldenstaedtii) from European aquaculture.

Abstract

Introduction: In Germany, around 150,000 kg of mostly Siberian sturgeon (Acipenser baerii), were produced in 2021. Sudden mortalities affected negative control Russian sturgeon in experimental infection of several European aquacultured fish species with tilapia lake virus (TiLV). An investigation sought the causative agent. In most of the sturgeon, a specific herpesvirus was detected which also occurred in the carp, crucian carp and tench subjects, but not in Nile tilapia. This herpesvirus was latent in the sturgeon population but became productive to cause the outbreak after three weeks of experimentation.

Material and methods: Different European aquacultured fishes were experimented upon. Chosen PCRs, nested PCRs and re-amplifications were carried out to identify the causative agent of the mortality event. Sequence analysis of the obtained PCR fragment and in-situ hybridisation (ISH) using tissue sections of the experimental fishes were performed.

Results: The PCRs used for detection of Acipenser herpesvirus (AciHV)-1 and -2 were always negative. An additional PCR assay with lesser specificity for AciHV found 118 of 123 sturgeon samples and some samples of cohabited cyprinids positive. The similarity of all isolates was 99.7%. The PCR results were confirmed by ISH using probes based on the same sequence, which detected identical viral sequences in both sturgeon and cyprinid samples. These findings revealed that a sterlet sequence previously deposited in the NCBI database had been incorrectly classified.

Conclusion: It seems that different herpesviruses and/or a new subspecies of AciHV are widespread in European farmed sturgeon populations, which, at least for aquacultured fish, opens up the possibility of vaccination against the disease which they cause. Additionally, a more specific diagnostic PCR has to be established.