A 3-yr field trial was conducted on 8 commercial swine farms in Illinois to determine the effectiveness of a feline Toxoplasma gondii vaccine in reducing the exposure of swine to T. gondii. A vaccine consisting of live bradyzoites of the mutant T-263 strain, capable of preventing oocyst shedding by cats, was used in this study. Each farm was visited 3 times in 1994, 3 times in 1995, and once in 1996. Cats were trapped and inoculated with the T-263 oral vaccine during 1994 and 1995. On each visit, the following samples were collected: blood from pigs, cats, and mice for detection of serum antibodies to T. gondii, feces from cats to detect oocysts, and heart and brain tissues from rodents to determine the presence of T. gondii tissue cysts. The modified agglutination test (MAT), with a positive titer set at the 1:25 dilution, was used to determine serum antibodies. At first capture, 72.6% (61/84) of juvenile cats and 32.6% (31/95) of adult cats had no detectable antibodies (seronegative), indicating no prior exposure to T. gondii when they received their first vaccine. Of these first-time seronegative cats, 58.1% (18/31) of adult and 45.9% (28/61) of juvenile cats were recaptured and received a second dose of vaccine. Changes in the prevalence of T. gondii infection were evaluated from the prevaccination (1992, 1993) to the postvaccination (1996) period. Eleven cats (5%) were detected shedding oocysts between 1994 and 1996, of which 10 (90.1%) shed during 1994. The last detection of oocyst shedding by cats was during the first farm visit in 1995. There was a significant decrease in T. gondii seroprevalence for finishing pigs (P < 0.05, Wilcoxon sign rank test). There was a positive correlation (Spearman's p = 1.0, P < 0.0001) between the change in prevalence in juvenile cats and the change in prevalence in finishing pigs. The seropositivity rate (MAT > or = 1:25) in mice among all farms decreased from 4% in 1992-1993 to 0% in 1996. The mean prevalence of T. gondii tissue cyst isolation for mice on all farms decreased from 1.1% in 1994, to 0.8% in 1995, and to 0.5% in 1996. The results of this study suggest that the reduced exposure of pigs to T. gondii was due to the administration of the T. gondii vaccine to cats.

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Previous studies have demonstrated that oral administration to cats of tissue cysts of the oocyst-negative mutant strain of Toxoplasma gondii, T-263, induces immunity to oocyst shedding following challenge. Experiments were designed to compare the levels of protection induced by T. gondii T-263 when tissue cysts, bradyzoites released from tissue cysts, and tachyzoites were administered to cats. In 1 experiment, groups of cats received 2 oral doses of intact tissue cysts or released bradyzoites of T. gondii T-263 and were challenged 47 days later with the oocyst-producing strain of T. gondii T-265. All cats seroconverted following immunization and none of them shed oocysts following challenge. In a second experiment, groups of cats received tachyzoites of T. gondii T-263 as a single oral dose and either 1 or 2 intraduodenal doses; they were challenged 60 days after the last vaccination. All cats seroconverted following immunization. Following challenge, all cats shed oocysts except for 2 of 7 cats that received 2 intraduodenal doses of tachyzoites. Thus, orally administered bradyzoites of T. gondii T-263, either contained in intact tissue cysts or liberated from cysts, induced immunity to oocyst shedding. In contrast, tachyzoites did not completely protect against oocyst shedding, even when delivered directly to the duodenum and despite the development of high antibody titers.

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This study was designed to identify changes in parasite-specific immune responses that occur during vertical transmission of Neospora caninum and can be used as indicators of parasite reactivation in naturally infected heifers. Ten heifers were unimmunized and 11 immunized with killed tachyzoites. One unimmunized heifer, which aborted at week 19 of gestation, had an increase in parasite-specific antibodies, mainly IgG(2), from week 15 to week 19 and a concomitant decline in parasite-specific cell-mediated immune (CMI) responses. Eight unimmunized heifers, which had live full-term congenitally infected calves, had an increase in antibodies, mainly IgG(2), from week 21 onwards. All immunized heifers delivered live full-term congenitally infected calves, and had a bimodal increase in antibodies; primarily IgG(1) following immunization and predominantly IgG(2) from week 17 onwards. Immunized heifers had significantly greater overall mean humoral and CMI responses than unimmunized heifers. Nine uninfected control heifers and their calves were seronegative. These results indicate that reactivation of a latent infection occurred in the naturally infected heifers, regardless of their immunization status, and was associated with increased parasite-specific antibodies, mainly IgG(2).

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The cerebrospinal fluid (CSF) obtained from patients suspected of having neurocysticerosis (79 samples), as well as from control patients (without neurological symptoms), was separated using a high performance liquid chromatography gel filtration column. During the chromatographic separation, the eluted fractions were collected separately according to distinctive peaks. The elution characteristics of CSF components were identified by aligning more than 100 chromatograms and 6 distinctive peaks, eluting in consistent positions. Samples of each peak were tested in an enzyme-linked immunosorbent assay (ELISA) for the presence of larval antigens. Forty-four of the suspected 79 cases were found to have larval antigens in their CSF and these antigens were detected in peak no. 2, the mean of which is approximately 110,000 molecular weight. Also, in some cases, larval antigens were found in peak no. 1; however, we were able to detect them in only 23 CSF samples out of 44 CSF samples in which larval antigens were present in peak no. 2. Nine of these 23 CSF samples (derived from 79 patients in which neurocysticercosis was suspected) were later confirmed by histopathology. Values of ELISA readings of 5 CSF samples obtained from control patients (0.054 +/- 0.064) were considered negative. Thus, in 44 of 79 CSF samples from patients suspected of having neurocysticercosis, the ELISA values were highly positive (0.551 +/- 0.293). The remaining 35 CSF samples gave ELISA readings of 0.092 +/- 0.062, which were not significantly different from values obtained with CSF of control patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Mice infected with Trypanosoma cruzi develop an early and profound immunosuppression of responses to heterologous antigens. Recently it has been demonstrated that this immunosuppression is linked, in part, to deficiency in the production of interleukin 2 (IL-2), and that the addition of IL-2 to cultures of normally unresponsive spleen cells from infected mice will restore responsiveness to sheep erythrocytes (SRBC) and enhance parasite-specific immune responses. In the present study, the effect of administration of ultrapure or recombinant IL-2 on immune responses to SRBC and parasite-specific responses in vivo was examined. It was found that a single injection of 1,500 U of IL-2 provided at the same time as SRBC more than doubled the number of direct plaque-forming cells to SRBC and that multiple injections of 1,500 U of IL-2 were no more restorative than a single injection. Anti-SRBC responses of normal mice were unaffected by injection of IL-2. Single or multiple injections of recombinant human IL-2, with and without gelatin, into highly susceptible C3H(He) mice induced greater parasite-specific immunity as reflected by significantly reduced levels of parasitemia and increased longevity. Three injections of 1,500 U each of recombinant human IL-2 on days 10, 14, and 18 was found to be the most efficacious in reducing parasitemia and increasing longevity. Injection of IL-2 with gelatin did not enhance the effect of IL-2 alone.