The histopathology of the reactions of calves to experimental infection with the nodular worm, Oesophagostomum radiatum (Rudolphi, 1803). I. Host reaction to re-infection with single large doses of larvae

Abstract

The histopathological aspects of the host response to Oesophagostomum radiatum were investigated following the reinfection of previously exposed calves. The elimination of third-stage larvae 18–22 hr after administration of the reinfecting dose was associated with oedema, hyperaemia, and hypersecretion in the intestine and was followed by a transient but intense diarrhoea. The infiltration of the oedematous intestinal tissues with eosinophil and neutrophil leucocytes and the vasculitis in the vicinity of the histotropic larvae indicated an Arthus type reaction. During the development of the third-stage larvae the exudative hyperergic inflammation changed to a proliferative granulomatous type. The moulting of the larva to the fourth stage was associated with a recurrence of oedema and vasculitis, and was followed by isolation and elimination of the larva and surrounding necrotic host tissue. If the larva was not discharged the healing was delayed and the nodular lesion persisted. The diarrhoea during the elimination of fourth-stage larvae was associated with oedema of the gut wall, hypertrophy, and profuse secretion of the mucosal glands. These changes developed to an excessive degree in the proximal 2 ft of the colon following the termination of the histotropic phase. The varying course of the enteric process was accompanied by simultaneous changes in the regional lymphatic tissue. Cell destruction, phagocytosis, and depletion of follicles during the acute phases alternated with lymphopoiesis during the proliferative reparative periods. The tissue damage from the exaggerated response to reinfection of a sensitized host resulted in anorexia and weight loss.