Proteases in blood-feeding nematodes and their potential as vaccine candidates.

Parasitic nematodes express and secrete a variety of proteases which they use for many purposes including the penetration of host tissues, digestion of host protein for nutrients, evasion of host immune responses and for internal processes such as tissue catabolism and apoptosis. For these broad reasons they have been examined as possible parasite control targets. Blood-feeding nematodes such as the barber-pole worm Haemonchus contortus that infect sheep and goats and the hookworms, Ancylostoma spp. and Necator americanus, affecting man, use an array of endo- and exopeptidases to digest the blood meal. Haemoglobin digestion occurs by an ordered and partly conserved proteolytic cascade. These proteases are accessible to host immune responses which can block enzyme function and lead to parasite expulsion and/or death. Thus they are receiving attention as components of vaccines against several parasitic nematodes of social and economic importance.