Histopathological characterization and in situ hybridization of a novel spiroplasma pathogen in the freshwater crayfish Procambarus clarkii

► Histological alterations in P. clarkii after spiroplasma infection were surveyed. ► A semi-quantitative histological assessment protocol was established. ► A new ISH application was described for the agent detection. ► Oligonucleotide probes presented here facilitated the detection. ► Findings are significant for studies on pathogenic spiroplasmas.