EVALUATION OF THE SAFETY AND EFFICACY OF VACCINATION OF NURSING RIGS WITH LIVING TACHYZOITES OF 2 STRAINS OF TOXOPLASMA-GONDII

The safety of vaccination and persistence and distribution of Toxoplas ma gondii stages within tissues following vaccination were examined in 3-day-old nursing pigs vaccinated with living tachyzoites by intraven ous and subcutaneous routes of either the TS-4 mutant strain or its pa rent RH strain of T. gondii. The efficacy of vaccination of nursing pi gs with the TS-4 mutant was also examined in pigs challenged orally wi th oocysts following vaccination. Pigs were vaccinated with 3 x 10(5) living tachyzoites when 3 days old and boosted with 3 x 10(5) living t achyzoites when 17 days old. Group 1 had 2 pigs vaccinated intravenous ly (i.v.) with Hanks' balanced salt solution (HBSS) and served as a va ccination control. Group 2 had 5 pigs vaccinated i.v. with tachyzoites of the TS-4 mutant; 3 pigs were used to examine the safety, persisten ce, and distribution of the TS-4 mutant and 2 were used for oocyst cha llenge. Group 3 had 5 pigs vaccinated i.v. with tachyzoites of the RH strain and all were used to examine the safety, persistence, and distr ibution of the RH strain within their tissues. Group 4 had 3 pigs vacc inated subcutaneously (s.c.) with tachyzoites of the TS-4 mutant; 1 wa s used to determine the persistence and distribution of the TS-4 mutan t within its tissues and the other 2 pigs were used for GT-1 oocyst ch allenge studies. Group 5 had 3 pigs vaccinated s.c. with tachyzoites o f the RH strain and all were used to examine the safety, persistence, and distribution of the RH strain within their tissues. None of the co ntrol pigs or pigs vaccinated with the TS-4 mutant developed clinical signs of disease or died prior to oocyst challenge. The TS-4 mutant wa s not reisolated from the tissues of vaccinated pigs nor were microsco pic lesions present in the tissues of pigs that had been killed and ex amined at necropsy. Severe disease with clinical signs consisting of d yspnea, inactivity, diarrhea, and ocular lesions was observed in the g roup 3 pigs vaccinated i.v. with the RH strain. One pig died 7 days af ter initial vaccination. Microscopic lesions were observed in numerous tissues of all group 3 pigs. Swelling, erythema, and ulcers were obse rved at the site of inoculation in the group 5 pigs that were vaccinat ed s.c. with the RH strain. Minimal to no microscopic lesions were obs erved in these group 5 pigs. The RH strain was reisolated from pigs in both groups vaccinated with this strain. Control pigs and pigs vaccin ated with the TS-4 mutant were challenged orally with 8 x 10(4) oocyst s of the GT-1 strain at 33 days of age. Vaccination with the TS-4 muta nt by intravenous or subcutaneous routes did not prevent tissue cyst f ormation in pigs following oocyst challenge. However, results of bioas says in mice indicated that pigs given the TS-4 mutant s.c. had fewer tissue cysts in their tissues after oocyst challenge.