Austwickia chelonae –associated cutaneous and plastron lesions in Chinese stripe-necked turtles ( Mauremys sinensis )

Between June 2020 and January 2022, 10 cases of shell rot with unknown etiology were investigated in Chinese stripe-necked turtles ( Mauremys sinensis ) from aquaculture farms in southern Taiwan. Histology revealed gram-positive filamentous bacteria within the dermis of the limbs and the shell bone, with all cases exhibiting shell ulceration. One unusual case also showed hepatic necrosis, with consistent bacteria isolated from the liver. Full-length 16S rRNA gene sequencing of our isolates demonstrated 99.7% similarity to the Austwickia chelonae type strain and complete identity to A. chelonae L16-18, previously isolated from Chinese crocodile lizards. To our knowledge, this represents the first report of natural infection with A. chelonae in M. sinensis . The findings suggest that A. chelonae infections may originate as cutaneous lesions, and in severe cases, the disease can progress to hematogenous spread to internal viscera, such as the liver.