Investigation of an idiopathic lesion in redclaw crayfish Cherax quadricarinatus using suppression subtractive hybridization

Lesions indicative of putative parvovirus infection were detected in a population of freshwater redclaw crayfish (Cherax quadricarinatus) displaying hypertrophied nuclei, while these changes were undetected in another population. These changes were characterised by hypertrophic nuclei with marginated chromatin but without Cowdry type A (CA) intranuclear inclusion bodies. Suppression subtractive hybridization (SSH) was performed to generate a cDNA forward library between the two populations of crayfish. A total of 323 sequences were analysed from SSH libraries. These sequences were grouped into 76 consensus sequences and clustered into 8 categories based on sequence homology from the NCBI GenBank database. Even though histopathological observations consistently revealed lesions presumptive of putative parvovirus in C. quadricarinatus as previously reported, the molecular method failed to confirm a viral aetiology. Despite the absence of viral gene detection and therefore a conclusion of an idiopathic aetiology, the health status of these two populations of redclaw crayfish was different, resulting in differentially expressed immune-related genes in the two populations, with some genes being up-regulated in the hypertrophied nuclei population. Furthermore, the absence of parvovirus from the SSH libraries indicates that perhaps the viral messenger RNA was in too low a concentration to be detected or does not have any poly(A) tail which the SSH methodology needs to function correctly