Investigation of Stellantchasmus falcatus metacercariae in half-beaked fish, Dermogenus pusillus from four districts of Chiang Mai Province, Thailand.

Half-beaked fish, Dermogenus pusillus, collected from Mueang, Hang Dong, Doi Saket and Saraphi Districts, Chiang Mai Province, were examined for their infection status with Stellantchasmus falcatus (Digenea: Heterophyidae) metacercariae. The infection rate of the fish was 100%. Fish in three of four districts were found only to have metacercariae of S. falcatus, whereas those in Saraphi District had mixed infections with metacercariae of Posthodiplostomum sp. The intensity of S. falcatus infection per fish varied; 652-1,342 (mean 999.5), 562-2,422 (1,323.1), 185-2,492 (502.6), and 22-550 (210.4) in Mueang, Hang Dong, Saraphi, and Doi Saket Districts, respectively. The body portions of the fish with the heaviest metacercarial infection were the muscles, in all districts. The present study confirms that half-beaked fish in Chiang Mai Province are heavily infected with S. falcatus metacercariae.

Metacercariae isolated from cyprinoid fishes in Khon Kaen District by digestion technic.

Several kinds of fresh-water fishes collected from natural water resources in Khon Kaen District were digested with 0.25% pepsin A to obtain the infective stage or metacercariae of fish-borne trematodes. Most of them harbored at least 3 species of trematodes. Two families of medical trematodes, i.e., Family heterophyidae and Family Opisthorchiidae, were isolated. The heterophyid flukes consisted of Haplorchis taichui, H. pumilio and Centrocestus formosanus. Opisthorchis viverrini was the only parasite of the Family Opisthorchiidae found in these fish. Among these four species, H. taichui was predominant and found in all kinds of fish examined, especially Hampala dispar.

Differential diagnosis of opisthorchiid and heterophyid metacercariae (Trematoda) infecting flesh of cyprinid fish from Nam Ngum Dam Lake in Laos.

The examination of flesh of 313 cyprinid fish from the Nam Ngum water reservoir in Vientiane Province, Laos, revealed the presence of four morphologically similar opisthorchiid and heterophyid metacercariae of medical importance. The following morphological characters, visible under dissecting microscope with low magnification, were typical of trematodes recorded in fish: (1) Opisthorchis viverrini, the liver fluke, has oval cysts containing quickly moving C-shaped metacercariae provided with a rather large excretory bladder; (2) metacercariae of Haplorchis pumilio and H. taichui are surrounded by a thin-walled, oval cyst; they are actively motile, C- or S-shaped, and possess a relatively small excretory bladder; (3) cysts of Haplorchoides mehrai are considerably variable in shape, size, and thickness of cyst wall; larvae are slowly moving, C- or S-shaped, or often not folded, and provided with a rather small excretory bladder. Some cysts with dead or degenerated H. mehrai larvae are filled with brownish or yellowish pigment. Morphological variability of some larvae, however, excluded correct identification of all metacercariae during routine examination of fish. Therefore, we consider isolation of several larvae from each fish host as well as all "atypical" metacercariae from fish flesh and their examination under the light microscope to be necessary. Even though this method of examination is rather time consuming, it decreases the possibility of false identification of trematode larvae encysted in flesh of cyprinid fish during field studies on opisthorchosis and heterophyiosis.

Occurrence of some medically important flukes (Trematoda: Opisthorchiidae and Heterophyidae) in Nam Ngum water reservoir, Laos.

Occurrence of some medically important flukes transmitted to man by eating of raw fish was observed at 18 localities of Nam Ngum water reservoir, an important source of fish for inhabitants of Vientiane Province, Laos. Cercariae of Opisthorchis viverrini were recorded in 0.9% of Bithynia siamensis goniomphalus examined but in the most populated sites, where the density of the snails was the highest up to 2.2% of the intermediate hosts were infected. Haplorchis cercariae were found in 2.0% of Tarebia granifera examined. O. viverrini metacercariae were found in flesh of four fish species (Hampala dispar. H. macrolepidota, Puntius gonionotus, Cyclocheilichthys repasson) from 9 localities with the highest prevalence (16%) in H. dispar. Metacercariae of Haplorchis pumilio and H. taichui were found in flesh of Hampala dispar, H. macrolepidota and Puntius gonionotus with the prevalence of infection 2-6%. Metacercarie of Stellantchasmus falcatus were localized in fins of Xenentodon canciloides. Domestic cats (Felis catus f. domestica) harbored the following trematode species: O. viverrini, H. pumilio, H. taichui, H. yokogawai, S. falcatus. Eggs of small flukes were found in stools of 44% of examined inhabitants of 3 villages and of the district center Thinkeo. The study revealed that the best predictor of the existence of small fluke foci and their species composition in the area studied was the second intermediate host-fish.