HAEMONCHUS-CONTORTUS - SOME FACTORS INFLUENCING THE DEGREE OF RESISTANCE OF SHEEP IMMUNIZED WITH ATTENUATED LARVAE

Adult worm-free sheep immunized with irradiated Haemonchus contortus larvae were highly resistant to challenge with 10 000 normal larvae. Administration of anthelmintic 1 week before challenge did not affect the degree of protection afforded by vaccination. Resistance was evident by 6 days after challenge in that larvae recovered from a group of vaccinated animals at this time were smaller than those found in the controls. However, it was found that a smaller proportion of the vaccinated sheep were resistant if the challenge dose was reduced from 10 000 to 500 larvae. Resistance to challenge was associated with the presence of IgA and IgG antilarval antibodies in the abomasal mucosa. Numerous globule leucocytes were present in the abomasal mucosa of most, but not all, immune animals. © 1979.