PATHOPHYSIOLOGICAL STUDIES OF SHEEP DURING THE BUILDUP OF IMMUNITY AGAINST OSTERTAGIA-LEPTOSPICULARIS AND AFTER A CHALLENGE INFECTION

Four groups of three lambs were used to investigate the pathophysiolog ical changes during the development of a protective immunity against O stertagia leptospicularis induced by a trickle infection. Three groups (A, B and C) were infected daily with 1000 third-stage larvae (L3) fo r a period of 26 weeks; group D remained uninfected until challenged. Egg excretion ceased after about 10 weeks in groups A, B and C and at the end of the trickle infection no parasites were found in group A sh eep after slaughter. The sheep of groups B and C were highly refractor y to two challenge infections, with 100,000 and 200,000 L3, given four and 17 weeks after the end of the trickle infection. Both challenge i nfections were followed by short term increases in the concentrations of gastrin and pepsinogen in the serum. Group C sheep were immunosuppr essed with flumethasone during the second larval challenge and had hig her pepsinogen concentrations but similar gastrin concentrations to th e untreated sheep of group B.