Dynamic pathology and pathogen distribution of the yeast Metschnikowia bicuspidata in the Chinese mitten crab (Eriocheir sinensis)

In this study, the “milky disease” model of Eriocheir sinhensis was constructed via intramuscular injection with the pathogenic yeast Metschnikowia bicuspidata. The dynamic pathological changes of E. sinensis after injection were elucidated with two staining methods (haemotoxylin-eosin and alcian blue periodic acid-Schiff) and fluorescence in situ hybridization technology. Anatomical observation revealed three stages of the “milky disease”: no clinical signs (1–4 days after infection), the appearance of signs of disease (5–7 days), and significant liquefaction (10 days). Histological observation also revealed three stages of the disease: yeast diffusion (1–2 days after infection), yeast slow development (3–4 days), and yeast rapid proliferation (5 days). And FISH technique was suitable for the early detection of infection with M. bicuspidata in E. sinensis. We found that M. bicuspidata spread to the whole body of the crab through the haemolymph and developed into fungal septicaemia. These results elucidate the systemic pathological characteristics of “milky disease” in E. sinensis and suggest the pathogenic mechanism of M. bicuspidata.