Neorickettsia-like organism isolated from metacercaria of a fluke, Stellantchasmus falcatus.

"Hyuga" fever, reportedly caused by Rickettsia sennetsu, occurring in the west of Japan was suspected to be an endoparasite-borne rickettsiosis. No R. sennetsu, however, was detected in metacercariae found in the muscles of grey mullets (Mugil cephalus) ingested raw by most "Hyuga" fever patients. Instead, another neorickettsia-like organism (SF strain) was isolated occasionally from metacercariae of Stellantchasmus falcatus. A dog was inoculated with SF strain. It developed mild fever after an incubation period of 10 days. No other clinical sign nor any macroscopic change upon autopsy was noted. The organisms were detected in its blood, lymph nodes and spleen, but not further transmissible. From these findings, the pathogenicity of SF strain to the dog seemed to be much lower than that of Neorickettsia helminthoeca or the Elokomin fluke fever agent of neorickettsia. These experiments support our presumption that SF strain may be a new member of neorickettsia, although no comparison of the antigenicity between SF strain and other neorickettsiae has been made.