Chapter 23 - Mitten crab tremor disease

Abstract

Pathogenic infections of rickettsia-like organisms (RLOs) though rare have been reported from marine crabs, Carcinus mediterraneus, Paralithoides platypus, and Lithodes aequispina. This discussion will focus on an important disease caused by an RLO in cultured freshwater Chinese mitten crab Eriocheir sinensis. The pathogen has since been identified as belonging to the genus Spiroplasma. RLOs occur in hemocytes and tissue cells of the muscle, connective tissue of pereiopods, heart and gut cells. Neurological symptoms may be related to RLO infection of the thoracic ganglion and myoneural junctions which affect nerve transmission. Crabs with signs of weakness have RLOs in the connective tissue of heart and gut, while crabs with tremor signs have RLOs in nerves and muscles. Experimental challenge and chemical studies against the spiroplasma of Chinese mitten crab tremor disease indicate that oxytetracycline injection at 40mg/kg crab produced 80% survival postinoculation challenge with the organism.