Development of morphological changes in the small intestine of lambs continuously infected with Trichostrongylus...

Groups of three-month-old worm-free Suffolk cross lambs were given 2500 Trichostrongylus vitrinus larvae on five days each week for four, six, eight and 13 weeks and killed one week later. Severe villous atrophy, epithelial erosion and cellular infiltration were common features in the duodenum and the following 2 to 3 m of intestine of lambs killed at weeks 5 and 7. There was evidence of intestinal recovery in the lambs killed at weeks 9 and 14; five of the seven lambs had large areas of intestine which appeared relatively normal and worm activity appeared to be confined largely within focal areas ("fingerprint lesions'). There was no change in the linear distribution of the worms in the intestine over the course of the experiment. The highest percentage of the larval challenge was recovered from lambs killed at week 5 and worm burdens were not cumulative. Lambs killed at week 14 were resistant to larval reinfection.