Review/Oorsig Volume 22, Issue 02 - Page 20

Oorsig/Review Wirevax: Vaccination against Haemonchus contortus in sheep Dr Hanre Ferreira Vaccination against helminths is a control concept that is currently being successfully applied in the control of Dictyocaulus viviparus (lungworm) infection in cattle in some parts of the world. Similar attempts have been made to develop vaccines against several economically important gastrointestinal nematodes in small stock and cattle (Ekoja & Smith 2010; Emery & Wagland 1991; Halliday & Smith 2011; Miller & Horohov 2006). The vaccine strategy that currently promises the most success largely ignores the mechanisms of natural immunity and attempts to direct responses towards external antigens (somatic antigens) on the outer surface (surface antigens) and in excretions and secretions (excretory- secretory antigens, ES antigens) of helminths. Candidate-protective antigens have so far been Circulating antibody, detected with a fluorescein conjugate, in lambs vaccinated with the gut membrane proteins purified from adult H.contorus binds to the microvillar surface of the instestinal cells of adult parasites. (Knox et al 2003) identified on the surface of oncospheres from Taenia and Echinococcus sp, and excretions and secretions of Fasciola hepatica, H. contortus and 20 Ostertagia ostertagi (Smith & Zarlenga 2006). In the case of blood-feeding Haemonchus sp, the luminal surface of the intestine has been a particularly rich source of suitable target molecules (Smith & Zarlenga 2006). In the most promising attempt to develop a vaccine against H. contortus in small stock, highly protective intestinal cell-membrane antigens, namely H-gal-GP and H11, have been identified and isolated at the Moredun Research Institute (Emery & Wagland 1991; Knox & Smith 2001; Smith 2008). H-gal-GP and H11 in Perspective Haemonchus galactose-containing glycoprotein complex (H-gal-GP) binds selectively to lectins and has a specificity for N- acetylgalactosamine. In each experiment, immunisation with H-gal- GP significantly reduced faecal egg counts (FECs) and wireworm burdens in vaccinated sheep compared to the unvaccinated controls. Immunisation was also significantly more effective against female than against male worms, as shown by the abnormal sex ratio of the populations recovered from each vaccinated group (Smith et al. 1999). H-gal-GP is an integral membrane complex of proteases derived from the microvilli of H. contortus intestinal cells. It is hypothesised that in vaccinated sheep, H-gal-GP antibodies ingested with the blood meal interfere with the worms’ digestion and leads to starvation of the parasites (Smith 2007). H11 is an integral membrane glycoprotein complex expressed exclusively in the intestinal microvilli of the parasitic stages. It is a highly effective immunogen against H. contortus challenge and has resulted in a 90% reduction