SEASONAL-VARIATION OF OPISTHORCHIS-VIVERRINI INFECTION IN CYPRINOID FISH IN NORTHEAST THAILAND - IMPLICATIONS FOR PARASITE CONTROL AND FOODSAFETY

Reported is the seasonal pattern of Opisthorchis viverrini metacercari ae in cyprinoid fish in north-east Thailand. Samples of fish were coll ected in 1991-92 at monthly intervals from two areas - Khon Kaen Provi nce, where the opisthorchiasis transmission rate was high, and Mahasar akham Province, where the rate was low. Metacercarial loads in both st udy areas had similar seasonal patterns. High burdens occurred in the late rainy season and winter (July to January) with low burdens during the summer (March to June). The average burden for Puntius leiacanthu s in Khon Kaen was 1.68 metacercariae per fish (127.43 per kg), higher than for all species of cyprinoid fish from the low transmission area . The intensifies of infection among P. leiacanthus and Cyclocheilicht hys armatus collected in Mahasarakham were comparable, but lower than the intensity of Hampala dispar (0.75 metacercariae per fish) concurre ntly sampled from the same area (P < 0.05). There was no significant d ifference in metacercarial load per kg between fish species from Mahas arakham. The results indicate that seasonal variation in metacercariae was a common phenomenon in areas with both high and low endemicity of infection. Also, the metacerarial load in fish was positively associa ted with infection levels among humans.