A Field Trial of the Effectiveness of a Feline Toxoplasma gondii Vaccine in Reducing T. gondii Exposure for Swine

Abstract

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.

A Comparative Analysis of Coprologic Diagnostic Methods for Detection of Toxoplama gondii in Cats

“…Furthermore, it may be used for the assessment of drugs used to prevent oocyst shedding by T. gondii -infected cats 40 or for monitoring the effectiveness of potential vaccines that would limit oocyst shedding in cats. 41 The results of the present study demonstrate the sensitivity, consistency, and infective-stage specificity of the copro-PCR. When combined with the previously demonstrated test sensitivity and specificity, 27 it can be concluded that the copro-PCR is at least as sensitive, consistent, and infective stage-specific as the bioassay.…”

Genetic characterisation of Toxoplasma gondii in wildlife from North America revealed widespread and high prevalence of the fourth clonal type

“…Toxoplasma gondii isolates from previously reported studies but not genetically characterised 2.1.1. Toxoplasma gondii isolates from rodents and cats from pig farms in Illinois, USA During the course of studies to determine sources of T. gondii infection on pig farms (Dubey et al, 1995), and methods to prevent T. gondii infection (Mateus-Pinilla et al, 1999), feral rodents and cats on these farms were examined for T. gondii infection. A decade later, some of these isolates were revived for the present study.…”

Veterinary vaccines against Toxoplasma gondii

“…The potential of this vaccine in the field was tested in a large scale trial conducted on young cats caught and trapped on eight commercial pig farms in the USA. The cats were vaccinated with the T-263 vaccine and the efficacy of the vaccine was measured indirectly by examining seroprevalence of other intermediate animal hosts, including the farmed pigs within the study farms (Mateus-Pinilla et al 1999). The results showed a decrease in seroprevalence within the pig population implying that vaccinating the cats had reduced the shedding of T. gondii oocysts into the environment and therefore reduced the source of infectious material for the intermediate animal hosts in this area (Mateus-Pinilla et al 1999).…”