Activity of known antischistosomal agents on early-developing forms of Schistosoma mansoni

Sixteen compounds, including several series of antischistosomal agents, were tested in mice (subcutaneous, oral, and intramuscular routes), previously injected intraperitoneally with 175 plus or minus 25 Schistosoma mansoni cercariae. Most drugs were given in a 5-day regimen, first dose being administered 3 hr before cercarial inoculation. Ten days after infection the animals were killed, the schistosomules collected from peritoneal washings, and counted under a dissecting microscopy (free organisms and larvae surrounded by macrophages). A high degree of activity (abscess of free larvae) was observed with Hoechst S-616 and S668, Ciba 17,581, Oxamniquine (Pfizer), and RD 12,869 compounds. A significant reduction (P less than 0.05) in the number of larvae was observed with A-16,612, Sb-EDTA, Hycanthone, Schistomide, Trichlorphone, and Antiomaline. No activity on nearly developing forms of S. mansoni was observed after treatment with Mirasan, Hoechst S-201, Schistocide T-109, Lucanthone, and Wellcome 153C51. In conclusion, from 16 compounds taken at random, all of which are active on mature schistosome infections, 11 displayed prophylactic activity. This indicates a high sensitivity of the technique using peritoneal schistosomules.