Sensitivity of isolates of Trichinella to the drug thiabendazole

Abstract

The sensitivity of three isolates of Trichinella spiralis (from pig, polar bear, and wolverine) and T. spiralis var. pseudospiralis to the anthelmintic thiabendazole (TBZ) was studied in male CD-1 mice. In vitro larval release by female worms isolated on day 7 following drug treatment (2–7 days) with various drug dosages (0.01–0.06%) showed that TBZ treatment resulted in sterility or a decrease in fecundity of the worms. Females of the pig isolate and T. spiralis var. pseudospiralis were chemosterilized with 0.05% TBZ and at 0.03% so were the two Arctic isolates (polar bear and wolverine), but chemosterilization was not permanent. Drug treatment during the disseminating phase (4–20 days) with low dosages (0.03–0.1%) was highly effective in reducing the number of muscle larvae at 40 days postinfection, a reduction that was similar for all Trichinella. Drug treatments (0.03–0.5%) during the early muscle phase (20–40 days) were ineffective with low dosages (<0.15%), but with a higher dosage (0.5%) 99 and 100% efficacy were noted for the two Arctic isolates and T. spiralis var. pseudospiralis, respectively. Larvae recovered at high dosages (>0.15%), were not infective to mice. Treatments with dosages of 0.03–0.1% from 40 to 60 days postinfection were only effective against the Arctic isolates. Of all the Trichinella studied, the pig isolate was the least sensitive to parenteral treatment.