Immunization of hamsters against Opisthorchis viverrini infection.

Attempts were made to induce acquired immunity against Opisthorchis viverrini infection in hamsters by immunizing them with aqueous somatic extract and metabolic products of adult worms, crude adult worm homogenates and metacercarial somatic extracts via either the intraperitoneal or combined intraperitoneal and oral routes. These procedures failed to stimulate significant protective response in animals that had never been exposed to O. viverrini. However, the protective response reached a significant level (30% worm reduction) in hamsters that had been infected with a small member of flukes prior to immunization with aqueous somatic extract of adult worms. Although these findings indicate that it may be possible to reduce reinfection in people in the endemic area by immunization, it appears that a better method currently available for the control of O. viverrini infection is health education aimed at changing food habits and improving sanitation and personal hygiene.

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.