Opisthorchis viverrini: ultrastructure of the tegument of the first-week juveniles and adult flukes.

The tegument of one-week-old and adult flukes of Opisthorchis viverrini were studied by transmission electron microscopy. The tegument of both stages is composed of a syncytium formed by processes of the tegumental cells lying underneath the outer-circular and the inner-longitudinal muscle layers. The tegument is bounded by trilaminate outer and inner membranes; the former is coated with a thin glycocalyx, while the latter has short basal infoldings. There are 4 forms of tegumental granules, namely dense spherical, dense discoid, light spherical and light discoid granules. Dense spherical and dense discoid granules have similar dense homogeneous and highly electron-dense matrices; thus, they may represent different planes of sections of biconcave granules, and may contribute their content to the formation of the outer membrane and the glycocalyx. Light spherical and light discoid granules may be another type of granule whose filamentous content may contribute to the formation of the microtrabecular network in the tegument. Microvilli start to develop in one-week-old juveniles and become fully developed in adult stages. The size, number and cristae of the mitochondria become increasingly more numerous along with the development of microvilli; in the first-week juveniles most mitochondria are located in the basal portion of the tegument while in adults most lie within microvilli underneath the outer membrane. The tegumental cell is irregular in shape and contains a nucleus with a prominent nucleus, abundant rough endoplasmic reticulum, well developed Golgi complexes, ribosomes, mitochondria and numerous tegumental granules.(ABSTRACT TRUNCATED AT 250 WORDS)