The effect of methionine and protein deficiency in delaying expulsion of Nippostrongylus brasiliensis in the rat.

Three protein-deficient diets containing 5%, 6%, or 7% casein, with and without 0.3% methionine supplementation, were fed to Wistar rats from weaning for 6 wk. Animals were infected subcutaneously with 1500 larvae of Nippostrongylus brasiliensis and killed after 14 days when nutritionally normal animals have expelled more than 97% of the worm burden. There was a delay in worm expulsion that was related to both the protein content (p = 0.0006) and to methionine content (p less than 0.0001). Methionine supplementation significantly reduced the worm burden in animals fed the 7% protein diet from a geometric mean of 32.4 to 5.2 (p = 0.0408) and in rats fed the 6% protein diet from a mean of 162 to 8.1 (p = 0.0002) but had no effect in rats on the 5% casein diet. Thus, addition of methionine overcame the adverse effect of protein deficiency in these less severely affected groups.