Conference Agenda

Increased drench resistance in sheep parasite populations necessitates alternative control measures. Unlike Barbervax, no vaccines exist for sheep scour worms. Detailed knowledge of protective immunity is essential for vaccine development designed to mimic natural host responses. In this study, 17-week-old parasite-naïve Merino lambs were exposed to weekly trickle infections of 6,000 infective Trichostrongylus colubriformis larvae for 16 weeks; controls remained parasite-free. After 16 weeks, mean faecal egg counts were 1518 and 0. Histologically, there was a time-dependent increase in intestinal goblet cells and decrease in jejunal mast cells in infected lambs. Flow cytometry at week 16 identified Ki67⁺GATA3⁺CD4⁺ T cells, indicating Th2 polarisation and expansion, with increased plasma and mucus anti-larval IgA and IgG. After drenching and challenge with 10,000 larvae, trickle-infected lambs rejected ~83% of larvae and had significantly lower worm burdens than controls. Anti-L3 T. colubriformis secretory IgA and IgG in bile may indicate portal immunoglobulin recycling from the gut. Additionally, in vitro antigen re-stimulation of cryopreserved intestinal cells showed increased Ki67⁺GATA3⁺CD4⁺ proliferating leukocytes with soluble L3 antigens. These results indicate 16 weeks of exposure creates a hostile intestinal environment for L3 establishment. Ongoing work assesses responses to L3/L4 antigens and associated ovine intestinal gene expression profiles.