Members of the genus  Oesophagostomum infect cattle, sheep and goats. In sheep and goats two species are present: O. columbianum and O. venulosum, the former being considerably more pathogenic. Only one species occurs in cattle: O. radiatum. The life cycle involves a sojourn in the mucosa of the intestine and it is during this larval histotropic phase that the genus has its most pathogenic effects. O. columbianum and O. radiatum infections produce lesions principally in the small intestine, while the other species mainly affect the large intestine (caecum, colon). Third-stage larvae penetrate deep into the mucosa and are enclosed into small  nodules (1–2 mm) by a fibroblastic reaction. The fourth moult occurs in these nodules. A strong reaction follows  superinfection, and larger nodules are produced (1–2 cm) with retention of L4 in the nodules for long periods.

The signs of oesophagostomosis are  anorexia, loss of body weight,  diarrhoea and sometimes oedema. A moderately...