First reported fatal Bacillus thuringiensis infections in Chinese soft-shelled turtles (Trionyx sinensis)

Recurrent outbreaks of an epizootic in Chinese soft-shelled turtles (Trionyx sinensis) in Zhejiang province, China in 2013, caused severe economic losses to turtle culture industry. This disease was characterized by listless swimming, craned or twisted neck, hyperemic laryngeal mucosa, and intumescent and hyperemic intestinal canal accompanied by mass mortality. Eleven diseased turtles with typical signs were collected from three distinct representative farms. Eleven bacterial isolates were collected from the livers and kidneys of diseased turtles and identified as Bacillus thuringiensis based on Vitek biochemical test, observation of rhizoid growth and protein toxin crystal production, 16S rRNA gene sequence analysis and Bacillus group species-specific PCR. These isolates demonstrated highly pathogenic potential to juvenile Chinese soft-shelled turtles with natural-infection-like symptoms. To our knowledge, this is the first case of B. thuringiensis infection in Chinese soft-shelled turtles and even in aquatic animals.