The effects of pregnancy and treatment with progesterone on the host–parasite relationship of Amplicaecum robertsi Sprent & Mines, 1960, in the mouse

Abstract

Male mice harboured more third-stage larvae of Amplicaecum robertsi than females; these larvae also grew longer than did those in female mice. Gonadectomy removed the differences, evident between the sexes, in both the numbers recovered and the growth of the third-stage larva, between male and female mice. The worms recovered from the gonadectomized hosts were smaller than those from the intact male and female host.Pregnant female mice harboured more worms than either the male or the non-pregnant female mouse. These worms were also smaller than those from the male and non-pregnant females. There was no difference in the growth of the larvae from gonadectomized and pregnant hosts.The treatment of spayed female mice with progesterone resulted in an increase in the size of worm population as compared with the numbers of worms recovered from intact female mice. The worms from the progesterone-treated spayed females were also longer than those from the spayed female hosts.Treatment of normal female mice with progesterone resulted in an increased recovery of worms compared with the numbers of worms recovered from normal female animals. The worms were stunted but they were of a size comparable to those recovered from pregnant female mice.It is suggested that the increase in the size of worm populations and the stunting of the worms recovered from pregnant female mice is associated with the effects of progesterone in relation to the hormone balance associated with the ovary at the time of pregnancy.