Secondary infections of Hymenolepis diminuta in mice: effects of varying worm burdens in primary and secondary infections.

In one (1 c) and six (6 c) cysticercoid primary infections of Hymenolepis diminuta in NIH (inbred) and CFLP (outbred) male mice 6 +/- 1 weeks old greater than 85% of the worms established but were rejected (destrobilated or expelled) subsequently. Rejection occurs more quickly in 6 c infections than in 1 c infections. Considerable worm growth occurs in 1 c and 6 c primary infections but worms from 6 c infections weighed less than worms from 1 c infections on all days studied. Expulsion of H. diminuta does not occur more rapidly in secondary infections than in primary infections; loss of 6 c secondary worms occurs at the same rate as 6 c primary worms but 1 c secondary worms survive longer than 1 c primary worms. Although worms are not lost more quickly in secondary than in primary infections, they are affected at an early age by the immune response which stunts their growth. Increasing the intensity of primary and secondary infections increases the severity of stunting of secondary worms. The results are discussed and it is suggested that immune responses to Hymenolepis spp. in rodents are common but that thresholds of worm numbers exist below which appreciable worm loss does not occur. Stunting due to crowding, which generally is attributed to inter-worm competition, may be in part immunologically mediated. For future immunological studies attempting to induce secondary responses to H. diminuta in mice, worm growth, not survival, is the criterion to evaluate.