The infectious agent is a trematode (fluke), Nanophyetus salmincola, and finding ova in fecal samples is diagnostic.
N salmincola is a carrier of the rickettsial infectious agent, but not all flukes carry the pathogen, so the presence of fecal ova is supporting evidence but not diagnostic.
The infectious agent, Neorickettsia helminthoeca, may be present in N salmincola at all stages of the trematodes life cycle.