Edwardsiella tarda: an intriguing problem in aquaculture

Edwardsiella tarda is a Gram-negative intracellular pathogen accounting for enormous economic losses in cultured seawater and freshwater fish. Infection by E. tarda often leads to the development of a systematic disease called edwardsiellosis, characterized by symptoms of ascites, hernia, exophthalmia, and severe lesions of internal organs. Although edwardsiellosis has been studied for many years, however, the major virulence factors of E. tarda are still poorly understood. In addition, the control of edwardsiellosis by antibiotics or formalin-killed bacterin was not as effective as that of extracellular pathogens such as Vibrio spp. More recently, great efforts have been put in studying the virulent factors of E. tarda, especially by scientists from China, and various candidate vaccines have been developed, some of which are very promising for cure of edwardsiellosis.