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Trichinella spp. and Toxoplasma gondii are important zoonotic parasites that infect warm blooded animals and humans worldwide. Among domesticated food animals, pigs are the main host for Trichinella spiralis. Pigs, chickens, sheep, and goats are known to be infected with T. gondii at varying rates, depending on husbandry. Infections in wildlife with these parasites are generally higher than in domesticated species. Feral swine act as reservoirs of infection in the sylvatic ecosystem for Trichinella spp. and T. gondii, acting as sources of infection for peridomestic carnivores whose home ranges overlap with domestic pigs. Feral swine can have direct contact with non-biosecure domestic pigs, presenting opportunity for direct disease transmission through cannibalistic behavior. Determination of the prevalence of Trichinella spp. and T. gondii infection in feral swine is needed to understand the risk of transmission of these parasites to domestic pigs. A cross-sectional serological survey was conducted between 2006 and 2010 to estimate the antibody prevalence of Trichinella spp. and T. gondii and risk factors associated with infection in feral swine in the USA. Serum samples were tested from 3247 feral pigs from 32 states; results are reported from 26 states. Maximum entropy ecological niche modeling and spatial scan statistic were utilized to predict the geographic range and to examine clusters of infection of Trichinella spp. and T. gondii in feral pigs. The seroprevalence of antibodies to Trichinella spp. and T. gondii was 3.0% and 17.7%, respectively. Species distribution modeling indicated that the most probable distribution areas for both parasites was similar, concentrated primarily in the South and the Midwest regions of the USA. A follow up survey conducted during 2012-2013 revealed that 2.9% of 984 sampled feral swine were seropositive for Trichinella spp., and 28.4% were seropositive for T. gondii. Three hundred and thirty (330) tongues were collected from the 984 sampled animals during 2012-2013; 1.81% were tissue positive for T. spiralis muscle larvae; no other genotypes were found. The potential exists for introduction of these pathogens into domestic herds of non-biosecure domestic pigs as a result of increasing overlap of the range of feral pigs with non-biosecure domestic pigs production facilities in the USA., (Published by Elsevier B.V.)

The United States Department of Agriculture (USDA) initiated the National Animal Health Monitoring System (NAHMS) in 1983 to collect, analyse and disseminate data on animal health, management and productivity in US domestic livestock populations, including swine. The programme includes an on-farm serological sampling component which can be used to monitor seroprevalence of various pathogens, including Toxoplasma gondii. The purpose of this study was to determine the seroprevalence of T. gondii in grower/finisher pigs using sera collected during NAHMS Swine 2006 and to determine farm level factors associated with differences in seroprevalence on farms where sera was collected during the Swine 2006 survey. Sera and data on management practices for this study were collected from 185 grower/finisher swine production sites located in 16 states accounting for > 90% of US swine production (Arkansas, Colorado, Iowa, Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Carolina, Ohio, Pennsylvania, South Dakota, Texas and Wisconsin). A total of 6238 sera were tested for T. gondii antibodies using a commercial ELISA assay (Vet. Parasitol.128, 2005, 177). Seroprevalence in this study, as determined by ELISA, was 2.6%, with a herd prevalence of 21.6% and a mean within-herd prevalence of 2.7%. Analysis of swine management practices indicated that rodent control methods and carcass disposal methods were associated with differences in the number of T. gondii positive samples on farm. These results are consistent with current epidemiological knowledge of the transmission of Toxoplasma on the farm (ingestion of organic matter containing oocysts, or ingestion of infected animal tissues). Production practices which eliminate these sources of exposure can reduce the risk of Toxoplasma infection in pigs, and reduce the likelihood of human infection from consumption of infected pork.

The prevalence of viable Toxoplasma gondii was determined in 6,282 samples (2,094 each of beef, chicken, and pork) obtained from 698 retail meat stores from 28 major geographic areas of the United States. Each sample consisted of a minimum of 1 kg of meat purchased from the retail meat case. To detect viable T. gondii, meat samples were fed to T. gondii-free cats and feces of cats were examined for oocyst shedding. Initially, 100 g of meat from 6 individual samples of a given species were pooled (total, 600 g), fed to a cat over a period of 3 days, and feces were examined for oocysts for 14 days; the remaining meat samples were stored at 4 C for 14 days (until results of the initial cat fecal examination were known). When a cat fed pooled samples had shed oocysts, 6 individual meat samples from each pool were bioassayed for T. gondii in cats and mice. Toxoplasma gondii isolates were then genetically characterized using the SAG2 locus and 5 hypervariable microsatellite loci. In all, 7 cats fed pooled pork samples shed oocysts. Toxoplasma gondii oocysts were detected microscopically in the feces of 2 of the cats; 1 isolate was Type II and the second was Type III. Analyzed individually, T. gondii was detected by bioassay in 3 of the 12 associated samples with genetic data indicating T. gondii isolates present in 2. The remaining 5 pooled pork samples had so few oocysts that they were not initially detected by microscopic examination, but rather by mouse bioassay of cat feces. Two were Type I, 1 was Type II, and 2 were Type III. None of the cats fed chicken or beef samples shed oocysts. Overall, the prevalence of viable T. gondii in retail meat was very low. Nevertheless, consumers, especially pregnant women, should be aware that they can acquire T. gondii infection from ingestion of undercooked meat, and in particular, pork. Cooking meat to an internal temperature of 66 C kills T. gondii.

The modified agglutination test (MAT) and a commercially available enzyme-linked immunosorbent assay (ELISA) were compared for detection of antibodies to Toxoplasma gondii in naturally-infected market-aged pigs. Infected pigs were obtained from commercial slaughter facilities and from farms where infection had previously been detected. Infection was confirmed by bioassay in cats. For 70 bioassay positive pigs, 60 were positive by MAT (85.7% sensitivity) and 62 were positive by ELISA (88.6% sensitivity). Of 204 bioassay negative samples 193 were negative by MAT (94.6% specificity) and 200 were negative by ELISA (98.0% specificity). Good correlation was seen between MAT and ELISA results. The results suggest that the ELISA may be a good tool for epidemiological studies of Toxoplasma infection on pig farms.

Retail meat cuts of pork are frequently enhanced with salt solutions to improve flavor and texture and to extend shelf life through reductions in microbial contamination. A study of the effect of commonly used meat enhancement solutions on the viability of Toxoplasma gondii tissue cysts was performed using tissues from experimentally infected mice and pigs. Brains of T. gondii-infected mice were injected to 110% of the original weight of the brain with solutions containing sodium chloride (1 and 2%), sodium diacetate (0.1 and 0.2%), sodium tripolyphosphate (0.25 and 0.5%), potassium lactate (1.4 and 1.96%), or sodium lactate (1.4, 1.5, and 2.0%) alone or in combination and stored at 4 degrees C for 7 days before feeding to T. gondii-seronegative cats. Loins were collected from pigs experimentally infected with T. gondii and injected as above and stored for 7, 28, or 45 days at 4 degrees C before feeding to T. gondii-seronegative cats. Cat feces were examined for 14 days to assess oocyst shedding. The present study demonstrated that injection of mouse brains or pork loins with solutions containing 2% sodium chloride or > or =1.4% potassium or sodium lactate, alone or in combination with other components, prevented transmission of T. gondii to cats.

Five recombinant Toxoplasma gondii antigens, designated B427, C51, C55, V22, and MBP30 were assessed for their potential use in an enzyme-linked immunoassay (EIA) for detection of T. gondii infection in swine. The antigens were evaluated with sera from young pigs that had been fed 1-10,000 T. gondii oocysts of the VEG or GT-1 strains. Results were compared with an EIA using a native T. gondii antigen extract. All 5 recombinant antigens, as well as native antigen, detected antibody responses as soon as 3 wk after infection in pigs inoculated with 1 or 10 oocysts of the VEG strain. This antibody response persisted, at varying levels, for 14 wk when the experiment was terminated. All antigens also detected antibody responses in pigs 4 wk after inoculation with 10,000 oocysts of the GT-1 strain. The antibody response recognized by native antigen remained high through 51 wk after inoculation. However, there was considerable animal-to-animal variation in responses to the individual recombinant antigens. Only antigens C51 and MBP30 consistently detected a positive antibody response over the entire 51-wk course of the experiment. These results suggest that these antigens might be useful for the serological detection of T. gondii infection in pigs.

Serum samples from 1788 horses slaughtered for food in North America were tested for antibodies to Toxoplasma gondii using the modified direct agglutination test (MAT). Antibodies to T. gondii were found by the MAT in 124 (6.9%) of 1788 sera; the titers were 1:20 (69 horses), 1:40 (37 horses), 1:80 (9 horses), and > or =1:160 (9 horses). A total of 339 selected horses were also tested by the Sabin-Feldman dye test (DT). Dye test antibodies were found in 54 horses with titers of 1:10 (29 horses) 1:20 (12 horses), 1:40 (4 horses) and 1:80 (9 horses). There was no correlation between the DT and the MAT.

To determine regional prevalence of infection with Toxoplasma gondii, 1897 pigs from 85 farms in five New England states were tested using a modified direct agglutination test. Sera were diluted 1:25 and a titer at this dilution was indicative of T. gondii infection. Farm management questionnaires were completed at the time of blood collection and were used to develop descriptive statistics on farms tested and to determine measures of association for risk factors for the presence of T. gondii-seropositive pigs. A total of 900 seropositive pigs were identified for a prevalence rate of 47.4%. Of 85 herds tested, 77 had at least one positive pig for a herd prevalence rate of 90.6%. Within herd prevalence ranged from 4% to 100% (mean = 48.4%). All farms studied had one or more risk factors for exposure to T. gondii. However, statistical associations with individual risks could not be made, most likely due to the extremely high prevalence. The results obtained here suggest that education on farm management practices to reduce exposure to T. gondii should be targeted to include small producers.

Serum samples from 143 hunter-killed black bears were collected during the 1996 and 1997 black bear hunting seasons in eastern North Carolina. All samples were tested for antibodies to Toxoplasma gondii by the modified agglutination test. Antibodies to T. gondii were present in 120 of 143 (84%) bears. Females had significantly higher titers than males (Wilcoxon rank sums test, P = 0.045), and titers increased with age (Jonckheere test, P = 0.01). Samples collected during 1996 (n = 79) were tested for antibodies to Trichinella spiralis by enzyme-linked immunosorbent assay. No samples were positive for antibodies to T. spiralis.

Serum samples from 509 pigs from 31 farms in Oahu, Hawaii were examined for antibodies to Toxoplasma gondii using the agglutination test in dilutions of 1:25, 1:50, and 1:500 and for Trichinella spiralis using the enzyme-linked immunosorbent assay. Toxoplasma gondii antibodies were found in 48.5% of pigs. Antibody titers were: 5.1% positive at 1:25 dilution, 28.6% positive at 1:50 dilution and 14.7% positive at 1:500 dilution. The prevalence of Toxoplasma gondii antibodies in garbage-fed pigs (67.3% of 199 pigs) was higher than in grain-fed pigs (33.8% of 180 pigs). Antibodies to Trichinella spiralis were found on seven of 31 farms. On five of these farms only a single serum was positive for Trichinella spiralis antibodies. The two remaining farms each had three positive sera (three of ten and three of 25 pigs tested); both of these farms fed garbage to pigs.

The passage of non-Toxoplasma antibodies from dam to fetus through damaged placenta was studied in sheep inoculated with Toxoplasma gondii. Six ewes were inoculated with chicken globulins and Leptospira bacterins 2 months before oral inoculation with Toxoplasma gondii oocysts. Ewes were euthanatized between 42 and 62 days after T gondii inoculation. Antibody titers against chicken globulins, Leptospira spp, Haemonchus contortus, Sarcocystis spp, and T gondii were measured in the maternal and fetal sera. All ewes became infected with T gondii and had grossly visible necrotic foci in the placentas, and T gondii antibodies were found in the fetuses and the ewes. Appreciable amounts of antibodies to Haemonchus contortus, Sarcocystis sp, Leptospira spp, and chicken globulins did not cross the placental barrier. Seemingly, serologic examination of the fetus was reliable for the diagnosis of ovine congential toxoplasmosis.