Abstract:
A vaccine for immunization of swine against Trichinella spiralis &#34;T. spiralis&#34; wherein the immunogenic substance is inert newborn larvae of T. spiralis emulsified with a suitable adjuvant. The vaccine induces greater than 60% immunity in swine and offers a novel approach to the control of swine trichinosis. Preferably, the inert newborn larvae preparation is emulsified with Freund&#39;s complete adjuvant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a vaccine for immunization against swine trichinosis. More particularly, this invention relates to a novel vaccine for swine trichinosis wherein the immunogenic substance is an antigen preparation of inert newborn larvae of Trichinella spiralis (&#34;T. spiralis&#34;). 
     2. Description of the Prior Art 
     Current strategies for controlling T. spiralis, the causative agent of trichinosis in swine, include antemortem and postmortem inspection and meat processing including curing, freezing and cooking. Yet, T. spiralis continues to cause the pork industry more than four hundred million dollars per year. Consequently, there exists a need for a more effective approach to the control of this parasite. 
     One such approach recognized in the prior art is the development of a vaccine for immunization against T. spiralis. Research on the antigens of this parasite has been encouraged toward this effort. For example, stichosome antigens derived from the muscle larvae and extracts of adult stages has been reported to be moderately effective in inducing immunity. D. D. Despommier [Parasit. Immunol. 3: 261-272 (1982)]; H. R. Gamble [J. Parasit. 71: 680-682 (1985)]. Isolation and characterization of stichosome antigens by immunoaffinity purification with monoclonal antibodies has also been achieved. H. R. Gamble [Exp. Parasitol. 59: 398-404 (1985)]; D. S. Silberstein et al. [J. Parasit. 71: 516-517  (1985)]; D. S. Silberstein et al. [Science 227: 948-950 (1985)]. However, these antigens have only been moderately protective in swine immunization trials. K. D. Murrell et al. [Vet. Parasitol. 15: 263-270 (1984)]; H. R. Gamble et al. [Am. J. Vet. Res. 47: 2396-2399 (1986)]. 
     It has also been shown that the surface of the newborn larvae of T. spiralis is antigenically diverse and stage specific, M. Philipp et al. [J. Exp. Med. 154: 210-215 (1981)]; M. Jungery et al. [Mol Biochem. Parasitol. 7: 101-109 (1983)], and that significant changes in the antigenic complexity of the newborn larvae surface occurs during its maturation. G. Ortega-Pierres et al. [Parasit. et al. Immunol. 6: 275-284 (1984)]. Further, antibodies to viable newborn larvae of T. spiralis have been shown to passively transfer protective immune response in rodents. D. D. Despommier [J. Parasitol. 57: 531-534 (1971)]. However, freeze-thaw killed newborn larvae were not effective in inducing aquired immunity in rodents. D. D. Despommier, Ibid. 
     The results of prior research does suggest the prospect of producing a vaccine against T. spiralis. However, until now there has been no vaccine which induces a significant level of immune response against T. spiralis in swine. 
     SUMMARY OF THE INVENTION 
     We have now developed a vaccine which unexpectedly produces greater than 60% protective immunity in swine against T. spiralis. The vaccine comprises inert newborn larvae of T. spiralis emulsified with a suitable adjuvant. The vaccine provides a method for immunizing swine against T. spiralis by inoculating the animal with an effective immunizing amount of the invention vaccine. 
     Accordingly, it is an object of this invention to provide a vaccine for swine trichinosis which produces a high level of protective immunity in swine. 
     Another object of this invention is to provide a method of immunizing swine against trichinosis through vaccination. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the means number of muscle larvae recovered, after challenge, from pigs immunized with T. spiralis whole newborn larvae (NBL/FCA) and saline controls (NaCl/FCA). 
     FIG. 2 shows the mean number of muscle larvae recovered, after challenge, from pigs immunized with T. spiralis whole newborn larvae, the soluble (Sol. NBL/FCA) and insoluble (Insol. NBL/FCA) fractions produced from the centrifiguation of whole newborn larvae, and saline controls. 
     FIG. 3 shows the results of enzyme-linked immunosorbent antibody assay for antibody in immunized and control pigs using various T. spiralis antigen preparations. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For purposes of the invention, the term &#34;newborn larvae&#34; is used herein to designate the first stage embryonic larvae produced by adult female T. spiralis prior to maturation and differentiation. The term &#34;inert&#34; is used herein to mean non-living newborn larvae of T. spiralis. 
     T. spiralis was maintained in female Sprague Dawley rats by serial passage. Muscle larvae &#34;L1&#34; were recovered by digestion, in 1:1 ratio pepsin-HCl (1% each), of eviscerated, ground rat carcasses and washed by settling through several cycles in warm water. Adult worms were recovered from intestines of rats six days post inoculation with infective L1. Recovery was accomplished using a modified Baermann apparatus with Hank&#39;s balanced salt solution at 37° C. 
     Adult female worms were incubated in Dulbecco&#39;s modified Eagle&#39;s medium (DMEM) supplemented with penicillin (250 units/ml), streptomycin (250 μg/ml), 2 mM glutamine, 1 mM Na-pyruvate, and 10 mM Hepes at 37° C. in 10% CO 2 . Newborn larvae were harvested after 24 hours by passage through a 44 μm mesh screen. Next, the larvae was washed in saline, centrifuged and frozen at -70° C. until further processing. The culture fluid supernatant containing the excretory secretory (&#34;ES&#34;) adult antigens may also be recovered, concentrated by filtration and stored at -70° C. 
     For use in pig immunization trials, frozen newborn larvae were thawed from -70° C. in a 37° C. water bath. Thereafter, the larvae was quick frozen in liquid nitrogen and thawed again at room temperature. Where soluble newborn larvae fractions and insoluble newborn larvae fractions were prepared, the thawed whole newborn larvae were disrupted by sonication following the quick freeze-thaw process, and separated in soluble and insoluble fractions by centrifugation using a Eppendorf microfuge. For purposes of the invention, the term &#34;soluble newborn larval fraction&#34; is used herein to designate the supernatant resulting from sonication and centrifugation of freeze-thawed whole newborn larvae. The term &#34;insoluble newborn larval fraction&#34; is used herein to designate the insoluble portion resulting from sonication and centrifugation of the freeze-thawed whole newborn larvae. 
     Whole freeze-thawed newborn larvae and soluble and insoluble newborn larval fractions were emulsified in Freund&#39;s complete adjuvant (FCA) to prepare the vaccine of the invention. Although FCA is the preferred adjuvant, it is within the compass of this invention to use any known adjuvant or emulsifier, e.g. aluminum hydroxide, to prepare the invention vaccine provided that the adjuvant does not significantly interfere with the effectiveness of the vaccine. 
     IMMUNIZATION OF PIGS 
     Groups of pigs were immunized in two trials, Trial 1 and Trial II, using the vaccine preparation of the invention. 
     The pigs used in each of the two trials were mixed breeds, male and female, from Hamshire x (Yorkshire x Duroc) dams and purebred Yorkshire or Duroc sires. Care was taken to distribute pigs evenly by size in each trial. 
     The vaccine of the invention was administered in 3 doses of antigen given intraperitoneally in a 1:1 volume ratio emulsion in FCA at weekly intervals. In Trial I, whole freeze-thawed newborn larvae were administered at 3.5×10 5  newborn larvae/dose/pig. In Trial II, either of whole newborn larvae, soluble newborn larval fractions and insoluble newborn larval fractions were given at 5×10 5  newborn larvae/dose/pig. Control groups of pigs in each of Trial I and II were injected with saline in FCA. 
     In both trials, pigs were challenged with 2000 infective L1 of T. spiralis one week after the last immunization. Six weeks after challenge, the pigs were killed, their tongue and diaphragm were digested, and worms were recovered therefrom. The number of L1 recovered was determined and expressed as larvae per gram of tissue. Statistical analysis of the L1 recovered for each of Trial I and Trial II is shown using Duncan&#39;s multiple range test (DMRT) in FIGS. 1 and 2, respectively. Ranking in DMRT is indicated by letters - groups with the same letter are not significantly different (α=0.05). 
     As shown in FIG. 1, pigs immunized in Trial I with whole T. spiralis newborn larvae preparation yielded significantly fewer L1 after challenge than did the saline controls. In Trial II, the strongest response occurred in pigs receiving whole newborn larvae and the insoluble newborn larvae. As shown in FIG. 2, reductions in L1 recovery from pigs immunized with whole newborn larvae and the insoluble fraction of newborn larvae were 88.2 percent and 85.5 percent, respectively, as compared to the saline controls. Pigs immunized with the soluble newborn larval fraction did not express a significant resistance to challenge. 
     Blood samples taken after the last immunization but prior to the challenge infection were analyzed by triple antibody enzyme-linked immunosorbent assay (ELISA) at a serum dilution of 1:20 in ELISA washing buffer. L1 ES antigens, ES antigens of adult worms, and the soluble and insoluble newborn larval fractions were used. As shown in FIG. 3, pigs receiving newborn larval antigens had, prior to challenge, antibodies that reacted with both newborn larvae soluble and insoluble fractions. The ES antigens of the adult and L1 stages did not cross-react with antibodies induced in the newborn larval immunized swine. 
     It is understood that modification and variation may be made to the foregoing disclosure without departing from the spirit and scope of the invention.