Trichinella spiralis: immunization of pigs with newborn larval antigens

The potential of crude Trichinella spiralis newborn larval antigens for pig immunization was investigated. A preparation of whole newborn larvae killed by freezing and thawing, and combined with Freund's complete adjuvant, induced a high level of protection against challenge (78%), compared to a 40% resistance level in pigs immunized with excretory secretory antigens of muscle larvae. Sera from pigs immunized with newborn larvae contained antibodies which bound to the surface of the newborn larvae, as determined by immunofluorescence. In a second trial, the freeze thawed newborn larvae preparation was compared with a soluble and insoluble fraction prepared by sonication of whole newborn larvae. Pigs receiving whole newborn larvae or the insoluble fraction developed strong immunity to challenge (88.2 and 85.5%, respectively); the soluble fraction was ineffective. Immunization with all preparations induced antibody to newborn larval antigens, but not to adult or muscle larvae excretory secretory antigens. Polyacrylamide gel electrophoresis of the soluble and insoluble fractions indicated that sonication was ineffective in solubilizing the larger molecular weight components. These results demonstrate that newborn larval antigens are highly protective in pigs, but that their further development as a vaccine will require more efficient procedures for antigen solubilization and large-scale production.