Two epidemics of water-borne diarrhoeal disease involving a total of 1000 persons are reported. In both epidemics, none of the usual bacterial entero-pathogens were recognized and Plesiomonas shigelloides was the only suspect aetiological agent isolated. The ecology of P. shigelloides was investigated in these outbreaks. It was recognized as an inhabitant of fresh surface water and its presence was closely related to warm weather.

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Median raphe cysts are derived from the external paraurethral ducts and contain features that to our knowledge have not been previously reported.

Enteropathogenicityof diarrhetic shellfish toxins (DST) was evaluated in rabbit intestinal loops, mouse intestinal loops and suckling mice, by using the methods established for the detection of bacterial enterotoxins.Crude toxin of DST (cr-DST) was prepared by acetone extraction from scallops (Patinopecten yessoensis) implicated in the poisoning outbreaks in Osaka in 1978 and 1982. Individual DSTs such as dinophysistoxin-1 and -3 (DTX-1 and DTX-3), pectenotoxin-1 (PTX-1) and okadaic acid were also tested on suckling mice for diarrheagenicity.The rabbit loop injected with 8 MU of cr-DST showed significant fluid accumulation in 18 hours. The mouse loop injected with 0.8 MU of cr-DST also showed significant fluid accumulation in 6 hours. In the suckling mouse test, positive results were observed with 0.1 MU of cr-DST in 4 hours.The small intestines with fluid accumulation in the loop tests were sectioned and stained with hematoxylin-eosin for histopathological studies. Destruction of epithelium and edema of the lamina propria were observed.In the suckling mouse test, DTX-1, DTX-3 and okadaic acid showed positive results, whereas PTX-1 did not.From these data, we concluded that DST shows enterotoxic activities in these animal models and that okadaic acid, DTX-1 and DTX-3 are diarrheagenic.

Median raphe cysts are derived from the external paraurethral ducts and contain features that to our knowledge have not been previously reported.

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