In the developed world, by far the greatest losses associated with parasitic infections are sub-clinical or economic. Antiparasitic drugs are used more often to maximise profits to salvage clinically sick animals (61). Such practices may be threatened in the future, due to a growing awareness that the extensive use of antibiotics could lead to the rapid emergence of drug-resistant pathogens, some of which could also pose a threat to humans. Consequently, a more recent approach has been to reduce the prophylactic use of drugs as much as possible, with a concomitant reduction of drug residues in biological products. The reasonable alternative is disease prevention by improved management practices, in which vaccination could play a pivotal role.