Endogenous Brevidensovirus-like elements in Cherax quadricarinatus: Friend or foe?

• Histology and polymerase chain reaction were conducted.
• Endogenous Brevidensovirus-like elements were found in Cherax quadricarinatus.
• These EBreVEs shared nucleotide and amino acid identities with IHHNV.
• The fragments are derived from the same region of an ancestral virus.
• These EBreVEs may have a protective function to their host.

Nine endogenous Brevidensovirus-like elements (EBreVE) were identified in redclaw freshwater crayfish Cherax quadricarinatus from different sources suggesting that these elements are widespread in redclaw in northern Queensland, Australia. These endogenous virus-like elements shared nucleotide identities (70–100%) and amino acid similarities (34–100%) with infectious hypodermal and haematopoietic necrosis virus (IHHNV) scientifically classified as Penaeus stylirostris densovirus (PstDNV). They may not have originated from IHHNV genomes, but could be derived from another uncharacterised member of the genus Brevidensovirus that share nucleotide similarities with IHHNV. The most striking feature of EBreVEs was that in each case, the segment (portion) of viral sequences inserted into the host genomes was from the same region of the viral genome and most likely derived from non-structural protein regions of ancestral virus, but they cannot be assembled into one consensus sequence. The EBreVEs may be inserted into the redclaw genomes following chronic or persistent infection by a corresponding virus that may have occurred as multiple independent integration events years ago leading to the accumulation of several integrated elements in their genomes. Histological examination and polymerase chain reaction (PCR) suggested that these insertions may have a protective function to their host.