Relationship between the efficacy of praziquantel treatment and the cystic differentiation in vivo of Echinococcus granulosus metacestode.

The cyst differentiation of protoscolices inoculated in NMRI mice was studied in detail. Although the laminated layer began its formation at 21 days post-infection (p.i.), we could not identify this structure in all parasites until 34 days p.i.. At 34 days p.i., all protoscolices were transformed into the metacestode stage. Subsequently, the efficacy of praziquantel (PZ) was studied in different stages of development of the parasite. We have found a different PZ susceptibility in both earlier stages and well-developed cyst. PZ treatment exhibited a high efficacy at the beginning of cyst differentiation and a zero efficacy in the mature metacestode when the cystic layers were totally developed. The relationship between the tegumental ultrastructural changes occurring during the vesicular evolution of protoscolices in NMRI mice and the efficacy of PZ treatment is discussed in the present study.