Morphology of spiroplasmas in the Chinese mitten crab Eriocheir sinensis associated with tremor disease.

The structure of spiroplasmas in the Chinese mitten crab associated with tremor disease was studied by transmission electron microscopy techniques, including both negative staining and ultrasectioning. A spiral structure, which is a typical form of spiroplasmas, could be detected and the observations showed for the first time the presence of spiroplasmas in the cells of the crab. Propagation of spiroplasmas within the cells presented various forms that could be sorted into three morphological types: rounded, regular helical, and pleiomorphic or intermediate forms.

A spiroplasma associated with tremor disease in the Chinese mitten crab (Eriocheir sinensis).

An epidemic of tremor disease has been a serious problem in Chinese mitten crabs, Eriocheir sinensis, in China in recent years. The disease-causing agent was previously considered to be a rickettsia-like organism. Here, analysis of the 16S rRNA gene sequence, light and electron microscopy and cultivation in vitro were used to identify the agent.