Host endocrine interactions with nematode infections. I. Effects of sex, gonadectomy, and thyroidectomy on experimental infections in lambs

Abstract

Male lambs were more susceptible to Oesophagostomum columbianum infections, harboring more and larger worms and producing fewer nodules than females. Gonadectomy removed these differences by increasing the susceptibility and worm growth in the female lamb. Thyroidectomy did not affect host resistance, as measured by nodule numbers, but did increase adult worm survival, particularly in the female host. This was attributed to decreased mucus production allowing more adult worms to survive in the thyroidectomized lambs. On first infection, many nodules were formed around the larvae by all the lambs, rather than around secondary bacterial infections. The average daily egg output per female worm was 11,300. Worms from normal female lambs produced more eggs than worms from other hosts. This was attributed to loss of worms, over the period of observation, giving an exaggerated result. Haemonchus contortus, a superficial migrator, did not show the same responses to the host endocrines as O. columbianum. Thus the conclusion was reached that parasites which have extensive somatic migrations in their life cycles are more likely to be affected by the hormone balance of the host than worms which do not have this somatic phase