A vaccine against the bovine lungworm, Dictyocaulus viviparus, was the first available anti-metazoan vaccine and is still used in Europe today (44). The vaccine contains irradiated L3-larvae that do not mature to adult worms. A similar approach was used to develop a vaccine against the canine intestinal nematode Ancylostoma caninum (34). Irradiation-attenuated larval vaccines were also developed against several gastrointestinal nematodes but they did not protect young, susceptible stock against infection and were, therefore, never commercialised (27). In general, these vaccines are difficult to produce as larvae must be harvested from the manure of infected animals.