Epidemiological study on Centrocestus armatus metacercariae in the Chikusa River, Hyogo Prefecture, Japan

ABSTRACT

The prevalence of <I>Centrocestus armatus</I> metacercariae in fresh water fishes were examined in Hyogo Prefecture, western Japan for a period of one year from April 2003 to March 2004. Three species of cyprinoid fish, namely <I>Zacco temminckii, Zacco platypus,</I> and <I>Pseudogobio esocinus,</I> were found to harbor metacercariae of <I>C. armatus.</I> The infection rate of metacercariae in <I>Zacco temminckii, Zacco platypus,</I> and <I>Pseudogobio esocinus</I> was 99% (371⁄377), 100% (8⁄8), and 100% (2⁄2), respectively. The mean number of metacercariae recovered was 232 for <I>Z. temminckii,</I> 2,123 for <I>Z. platypus,</I> and 20 for <I>P. esocinus.</I> However, we focused on <I>Z. temminckii</I> in this study because it was found to be the most predominant fish species in the Chikusa River and to have high a metacercariae prevalence as well. <I>In Z. temminckii,</I> metacercariae were distributed in the brain (37%), viscera (35%), muscles (29%) and gills (0%). No metacercariae were recovered from the scales and fins. This is the first report of the occurrence of <I>C. armatus</I> metacercariae in the brain region of the second intermediate fish. The prevalence of <I>C. armatus</I> metacercariae was almost constant throughout the year, and no positive correlation was found between the prevalence and seasonal changes. However, a positive relationship was observed between prevalence of metacercariae and fish length, I.e., the intensity of infection increases with the size of the fish host (p < 0.05). People in the survey area sometimes eat fish raw, indicating enlightenment as well as the countermeasures to prevent <I>C. armatus</I> infection is needed.