Study on Schistosoma sinensium in Fang district, Chiangmai province, Thailand.

A survey on human infection and possible natural definitive host of Schistosoma sinensium was carried out in Fang District, Chiangmai Province, North Thailand, where Tricula bollingi snails which harbour cercariae of S. sinensium inhabits. Stool examination of the people in the two villages along the stream, where T. bollingi were found, was by formalin-ether concentration technique and by Stoll's method. The stools were found to be negative for S. sinensium eggs. Field rats were also trapped and examined for the presence of S. sinensium. Adult worms and eggs of S. sinensium were found in the mesenteric veins and livers, respectively, of the field rats, Rattus rattus, captured in the rice fields along the stream.

Humoral immune responses in hamsters infected with Opisthorchis viverrini.

The kinetics and nature of humoral immune responses to somatic and excretory-secretory (ES) antigens were investigated in hamsters experimentally infected with different numbers of Opisthorchis viverrini. ES antigens were obtained from the in vitro culture of adult flukes and somatic antigens were aqueous extracts of adult flukes. Antibodies in the serum and bile of infected animals were determined by the microhaemagglutination technique, using glutaraldehyde fixed sheep red blood cells sensitized with these parasite antigens. Antibody responses to both somatic and ES antigens were detected in the serum from the second week of infection onward. The peak response was noted at the end of the second month and declined slowly thereafter. Antibody levels in animals with heavy infections (100 metacercariae) appeared earlier but declined more rapidly than in animals with light infections (25 metacercariae). The serum antibodies were highly sensitive to mercaptoethanol throughout the course of infection (23 weeks). Antibodies also appeared in the bile obtained at the time of sacrifice but their titres were rather low compared with those in the serum. Like serum antibodies, biliary antibodies were reactive with both somatic and ES antigens. Biliary antibodies were of the secondary IgA type. These findings are discussed in relation to pathogenesis of the disease process and to the possible usefulness in immunodiagnosis.

Opisthorchis viverrini : intensity and rates of infection in cyprinoid fish from an endemic focus in Northeast Thailand.

The infection rates and monthly variations in intensities of Opisthorchis viverrini infection in cyprinoid fish from an endemic focus in Northeast Thailand were investigated between April 1980 and March 1981. Out of six species of cyprinoid fish examined, four were found to harbour O. viverrini metacercariae. All four species of infected fish showed high rates of infection. Among the four species of O. viverrini infected fish, Cycloccheilicthys apagon and Puntius leiacanthus were found in abundance. The results indicate very little variation in the rates of infection throughout the year. On the other hand, intensities of infection varied from month to month, ranging from 8 to 88 metacercariae per fish for C. apagon and from 8 to 32 metacercariae per fish for P. leiacanthus. O. viverrini metacercariae were found in the fish muscle throughout the body; however, the body muscle harboured the highest density of metacercariae, followed by the dorsal fin, pectoral fin, pelvic fin and anal fin muscles respectively. In lieu of all these findings, it is therefore invalid to assume as indicated by the former workers that any potential intermediate fish host that does not have the O. viverrini metacercariae in its pectoral fin muscle in negative with opisthorchiasis.