Development of larval Echinococcus granulosus confronted with chicken heart tissue in vitro

Vesiculated protoscoleces (VP) were produced by culturing freshly collected protoscoleces from Echinococcus granulosus horse liver hydatids in RPMI 1640 monophasic medium at 37 degrees C for 18 days. Half of the VP were used as such, the other half used after killing them by freeze-thawing. Nine-day-old chicken heart fragments (CHF) were cultured in MEM at 37 degrees C for 72 h. Subsequently, CHF were put together with live and dead VP, respectively, for up to 53 days, on a semisolid medium consisting of agar, Ringer's and MEM. Time-dependent histological observations revealed that dead VP were surrounded by CHF cells. Dead VP tissue was eventually internalized and disintegrated in about 1 week. Live VP penetrated into the CHF tissue and further developed into small hydatid cysts, located within the boundaries of the experimental 'host' tissue. The amorphous-looking contact region PAP-stained positively only with anti-E. granulosus serum and not with anti-CHF serum; it was considered identical to the normal laminated layer. The invasion of VP in CHF tissue proved to be different from a tumour or a bacterial invasion: it was concluded that the confrontation of VP and CHF had resulted in an 'in vitro cohabitation' rather than in an 'in vitro infection'.