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

Abstract

In one (1c) and six (6c) cysticercoid primary infections of Hymenolepis diminuta in NIH (inbred) and CFLP (outbred) male mice 6±1 weeks old > 85% of the worms established but were rejected (destrobilated or expelled) subsequently. Rejection occurs more quickly in 6c infections than in 1c infections. Considerable worm growth occurs in 1c and 6c primary infections but worms from 6c infections weighed less than worms from 1c infections on all days studied.Expulsion of H. diminuta does not occur more rapidly in secondary infections than in primary infections; loss of 6c secondary worms occurs at the same rate as 6c primary worms but 1c secondary worms survive longer than 1c 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.