Swine immunity to selected parasites.

Swine parasitism exerts a significant economic impact worldwide. In the United States, the greatest losses are due directly or indirectly to the costs of zoonotic parasitisms. Three of the six most common foodborne parasitic diseases of humans in the United States are associated with pork consumption. These include toxoplasmosis, taeniasis or cysticercosis (caused by the pork tapeworm Taenia solium), and trichinellosis. Toxoplasmosis is of particular concern because of the fulminating disease that occurs in immunocompromised people. Generalizations and extrapolations of information derived from rodent and human studies, to swine parasitisms, are complicated by immunological differences between the hosts, and by the diverse biological characteristics of internal and external parasites studied. Swine studies thus far reported have demonstrated that protective immunity to helminth infection involves both cellular and humoral mechanisms, with antibodies and antibody-mediated responses playing important roles in preventing establishment of newly acquired larvae. Protection against protozoan parasites is primarily by cell-mediated strategies, whereas protective immunity to arthropod infestation is primarily through humoral mechanisms, principally those associated with type 1 hypersensitivity.