REJECTION OF HETEROLOGOUS NEMATODES BY SHEEP IMMUNIZED WITH LARVAL ORADULT TRICHOSTRONGYLUS-COLUBRIFORMIS

Rejection of heterologous nematodes by sheep immunized with larval or adult Trichostrongylus colubriformis. International Journal for Parasi tology 23: 841-846. Sheep immunized by truncated larval infections or by the adoptive transfer of adult Trichostrongylus colubriformis were subsequently challenged with single infections of T. colubriformis, Ne matodirus spathiger, Haemonchus contortus or Ostertagia circumcincta o r combinations of the parasites. Sheep vaccinated with larval infectio ns were >90% protected by 4 days after challenge (DAC) against T. colu briformis L(3) given in a single or combined infection, whereas no sig nificant protection was exhibited against a single-species infection w ith the unrelated nematodes N. spathiger or O. circumcincta. Sheep cha llenged with T. colubriformis together with N. spathiger or O. circumc incia were equally protected against both intestinal nematodes, but O. circumcincta was not affected. Sheep immunized with adult T. colubrif ormis and challenged with a combined infection of T. colubriformis, N. spathiger and H. contortus expelled around 40 and 80% of the intestin al parasites by 4 and 11 DAC, respectively, but showed no protection a gainst the abomasal parasite, H. contortus. The results confirm the pr evious findings on `self-cure' and the non-specific rejection of unrel ated parasites living in the same or downstream niches in the gut when the nematode used to induce immunity is included in the challenge inf ection. The results also indicate that even though L, antigens effecti vely elicited the non-specific rejection, antigens produced by L(3) an d later stages could also induce rejection of unrelated worms in the s econd week after infection.