The parasite burden in the liver and peritoneal cavity, and antibody levels directed to whole worm extract, have been monitored in serum from ICR-strain mice, infected orally with 55 tetrathyridia of Mesocestoides corti (Cestoda, Cyclophyllidea). The subcurative doses (3x or 6x) of praziquantel (PZQ) (10 mg . kg(-1) body weight) were administered to mice from day 14 post infection (p.i.) in two drug formulations: as PZQ suspended in Dorfman vehicle, or as PZQ incorporated in Liposomes (lip.PZQ). The appearance of antibodies was time-dependent and correlated with the rate of reduction in numbers of tetrathyridia. PZQ in three and six doses caused the highest fall of parasite numbers in the liver on day 1 post therapy (p.t.). In the peritoneal cavity, a similar reduction in worm burden occurred but only after six doses of the drug. The worm count in the peritoneal cavity from groups of mice injected with Lip.PZQ decreased most markedly on day 7 p.t., in the group treated with six doses of the drug. In the liver, the highest larvicidal effect, compared with the controls, was observed 6 days later (i.e. day 13 p.t.), following three doses of lip.PZQ. In all treated groups, two peak values of antitetrathyridial antibody levels were detected between days 1 and 13 p.t. (i.e. days 17 to 29 p.i.), after which there was a gradual but continuous increase in antibody titre. After treatment with six doses of both drug formulations (PZQ and lip.PZQ), the occurrence of the first maximum and minimum of antibody serum levels was delayed 6 days, compared to those groups treated with three doses of the drugs. Empty liposomes had some immunomodulatory effect on the antibody response, with significant decrease in antibody titres after three doses over the experimental period, but not after six doses.
