Studies on Schistocephalus solidus. II. Establishment and longevity in the definitive host

Abstract

Schistocephalus solidus was found to mature in ducks ( Anas boschas), pigeons ( Columba livia), chickens ( Gallus domesticus), herring-gull ( Larus argentatus), blackheaded gull ( L. ridibundus), rats ( Rattus norvegieus), and hamsters ( Mesocricetus auratus). The age of the host was important in determining the percentage of worms to become established. Best results were obtained with 1–4-weeks-old ducks (over 50% established) and 2–5-weeks-old chickens (nearly 40% established). Examination of the distribution of worms in the intestine of the various laboratory hosts showed: (1) worms reach the intestine in 2–3 hours; (2) within the first 6 hours the worms occupy a specific region of the intestine which varies in the different hosts, e.g., posterior half of duck's intestine, anterior half of pigeon's, near the cecum in rat, and anterior third of small intestine in hamster; (3) in those hosts in which the worms occupy an anterior position there is evidence of an initial overshoot followed by an anterior migration. The length of life appears specific within a host species but differs greatly between species of host: approximately 18 days in hamsters, 6 in rats, 14 in chickens, 11 in ducks, and 10 days in pigeons. The following points are discussed: (1) the advantages and disadvantages in the use of the different laboratory hosts; (2) the problem of how Schistocephalus, which lacks hooks and suckers, can retain its position in the intestine; and (3) the factors which determine longevity, viz., senility changes, immunity reactions, and environmental risks. Present evidence suggests the longevity of Schistocephalus is limited by senility changes.