Metacercaria from freshwater fishes of Mae Sa stream, Chiang Mai, Thailand.

Metacercaria from freshwater fishes of Mae Sa stream, Doi Suthep-Pui National Park. Chiang Mai Province were investigated between January 1997-December 1998, 3,133 fishes of 32 species were collected. The prevalence of infection of fishes was 19.087% (598/3, 133). Six genera of metacercaria were recovered as follows: Acanthostomum sp, Centrocestus caninus, Haplorchis taichui, Haplorchoides sp, Posthodiplostomum sp and Stellantchasmus falcatus. The prevalence of each species of metacercaria was observed from total number of fishes as follow: 1.149% (36/3,133), 3.753% (96/3,133), 1.883% (59/3,133), 9.735% (305/3,133), 0.096% (3/ 3,133) and 2.553% (80/3,133) respectively. The highest prevalence of parasites were observed: Acanthostomum sp was 11.111% from Trichopsis vittatus; Centrocestus caninus was 100% from Xenentodon cancila; Haplorchis taichui was 12.108% from Mystacoleucus marginatus; Haplorchoides sp was 55.532% from Mystacoleucus marginatus; Posthodiplostomum sp was 1.176% from Dermogenus pusillus; Stellanchasmus falcatus was 100% from Xenentodon cancila. Centrocestus caninus, Haplorchis taichui and Stellantchasmus falcatus have been reported from human and mammals. The rest were reported from birds, fishes and reptiles.

Effect of niclosamide on the tegumental surface of Haplorchis taichui using scanning electron microscopy.

The effect of niclosamide on the tegument of adult Haplorchis taichui (Trematoda: Heterophyidae) exposed in vitro was observed by scanning electron microscope. Adult worms were incubated in Tyrode's solution containing 0.01, 0.1, 1.0, and 10 microg ml(-1) of niclosamide for 30 min, 1, 6, 12 and 24 h. Control groups were incubated in Tyrode's solution without niclosamide and worms remained active until 24 h. In 0.01 microg ml(-1) of niclosamide, worms showed slightly active movements up to 1 h after incubation, while in 0.1 microg ml(-1) solution a few worms showed only slightly active movements after 30 min. Tegumental changes were determined by scanning electron microscopy. Swelling and blebbing of the tegument were observed on both ventral and dorsal sides. After longer periods, extensive swelling and blebbing of the tegument became more severe and there was a loss of the apical plasma membrane in some regions. Empty spine sockets occurred, and small perforations penetrated the basal lamina, followed by some lesions. Destruction of both surfaces was more pronounced on the posterior compared with the anterior regions.