Parasitology
Towards a vaccine for Haemonchus contortus, an
important nematode parasite of sheep
Smith, D
Worldwide, Haemonchus contortus is the most important nematode parasite of sheep and goats. Worms resistant to the anthelmintic drugs normally used for controlling this species are now widespread and the problem is increasing inexorably. Alternative methods for control are urgently required.
One possibility is control by vaccination, but currently there are no commercially available vaccines for any gastrointestinal nematode parasites of any host, including man. Previous work at Moredun Research Institute has identified several protein digesting enzymes from the intestinal cells of Haemonchus which are vaccine candidates, but it would not be economic to produce a commercial vaccine which contained natural worm proteins. The solution is to manufacture them cost effectively by molecular biology techniques.
Very recently one of these enzymes, artificially synthesised in yeast, was modestly successful when used experimentally as a vaccine for sheep infected with Haemonchus . A major aim of the project will be to improve on this effect, either by synthesising different forms of the same enzyme and/or by using it in combination with one or more of the other candidates. Parallel work will attempt to identify a suitable vaccine adjuvant and determine whether the vaccine could act synergistically with anthelmintics to prolong the use of these against drug resistant worms. In collaboration with Australian parasitologists, the potential of a prototype vaccine will be evaluated under practical farming conditions in a part of New South Wales where haemonchosis and drug resistance are rife.