First detection and analysis of a fish circovirus

Area of Science:

• Veterinary Virology
• Aquatic Animal Health
• Molecular Biology

Background:

• Circoviruses are globally prevalent in avian and swine populations.
• Their presence and impact in fish species remain largely undocumented.
• Recent unexplained mortality events in barbel fry (Barbus barbus) in Hungary prompted investigation.

Purpose of the Study:

• To investigate the cause of increased mortality in barbel fry.
• To detect and characterize novel viral agents in affected fish populations.
• To determine the phylogenetic placement of any newly discovered viruses within the Circoviridae family.

Main Methods:

• A circovirus-specific, wide-range nested PCR assay was employed for viral detection.
• Whole genome sequencing was performed on two distinct viral isolates.
• Bioinformatic analysis was used to determine genome characteristics and phylogenetic relationships.

Main Results:

• Two previously unknown circular viral DNA genomes, designated Barbel circovirus 1 (BaCV1) and BaCV2, were detected in barbel fry.
• These viruses possess a genome size of 1957 bases with two major open reading frames (ORFs).
• Phylogenetic analysis places BaCV1 and BaCV2 in a distinct new genetic group within the Circoviridae family, separate from known circoviruses.

Conclusions:

• This study reports the first discovery of circoviruses in fish, specifically in European barbel.
• The identified viruses represent a novel genetic lineage within the Circoviridae.
• A direct causal link between the detected circoviruses and the observed barbel fry mortality could not be established in this study.