Long-term humoral antibody responses by various serologic tests in pigs orally inoculated with oocysts of four strains of Toxoplasma gondii

Seroprevalence of Toxoplasma gondii in wild boars (Sus scrofa) hunted in Ukraine

Toxoplasma gondii is an important zoonotic parasite worldwide, but it has received limited attention in Ukraine. A seroepidemiological study was conducted and samples from 452 wild boars that had been hunted in 2006-2011 in 23 of the 25 regions of Ukraine were tested to estimate T. gondii seroprevalence. A locally available commercial enzyme-linked immunosorbent assay (ELISA) was used for the investigation. Additionally, we tested 92 of the sera using a widely used commercial multi-species ELISA and an indirect immunofluorescence antibody test (IFAT). With the locally available ELISA, 35 of the 452 wild boars tested positive, yielding a seroprevalence estimate of 7.7% (95% confidence interval 5.5-10.5). The seropositive wild boars originated from eight of the regions. Using the majority criteria, 10/92 samples tested using both ELISAs and the IFAT were considered positive, yielding an estimated seroprevalence of 10.9% within the subset of samples. The highest seroprevalence was observed in wild boars hunted in Luhans'k (30.0%), Odesa (17.7%) and Kharkiv (12.7%). Seroprevalence was higher in older animals (13.3% for age group >12 months and 7.7% for age group ≤12 months). This is the first seroepidemiological study of T. gondii in wild boars in Ukraine. Assuming that seropositivity indicates presence of infectious parasites in the tissues, eating undercooked meat of wild boars hunted in Ukraine could be a potential source of infection to other hosts, including humans.

Toxoplasma gondii Survey in Waterfowl and Gulls from Eight USA States

Sera from 391 waterbirds from eight USA states were tested for Toxoplasma gondii antibodies using the modified agglutination test. Fifteen different waterbird species (26.6%; n=104) were seropositive. Of the adults, 25.4% (n=52) showed a significantly higher T. gondii seroprevalence compared with juveniles (13.4%; n=17); however, sex was not a significant factor.

Seroprevalence of Toxoplasma gondii infection in slaughter pigs in Shanghai, China

Toxoplasma gondii is a pathogen that seriously threatens the health of humans and animals. However, the current infection status of T. gondii in slaughter pigs in Shanghai is still not clear. To investigate the seroprevalence of T. gondii infection and analyze the prevalence factors associated with the parasite infection, 1158 serum samples were collected from five slaughterhouses in three districts between 2015 and 2018. Serum antibodies against T. gondii were detected in 160 pigs (13.8%) by enzyme-linked immunosorbent assay (ELISA). Additionally, seroprevalence rates differed among different districts (ranging from 4.0% in JD-2 to 17.6% in JD-1), seasons (ranging from 6.7% in winter to 17.8% in autumn), and years (ranging from 8.0% in 2016 to 26.8% in 2015). Region, season, and year were the main factors affecting T. gondii infection in these pigs. There were few reports on serological monitoring of T. gondii in Shanghai slaughterhouses between 2015 and 2018, and the number of infections had steadily increased over the past several consecutive years. Therefore, our data are helpful to understand the epidemic status of T. gondii in Shanghai, which will strengthen the prevention and treatment of swine toxoplasmosis.

Large-scale serological screening of slaughter pigs for Toxoplasma gondii infections in The Netherlands during five years (2012-2016): Trends in seroprevalence over years, seasons, regions and farming systems

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The seroprevalence of T. gondii in slaughter pigs was between 1.4% and 2.8%.

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The seroprevalence of T. gondii in slaughter pigs showed a peak in winter.

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Pigs from organic farms had a higher seroprevalence of T. gondii.

Toxoplasma gondii is the causative agent of the parasitic disease toxoplasmosis, which is an important foodborne zoonosis. Eating undercooked meat of infected animals, including pigs, has been considered the major transmission route of T. gondii to humans. Therefore, it is urgent to develop and implement intervention measures in the pork meat chain to reduce risks of acquiring a T. gondii infection. Proposed measures for control of T. gondii in pigs include serological testing of pigs and audits of pig farms on risk factors for T. gondii infection. So far, these ideas have not been tested in practice. In order to generate knowledge about the epidemiology and seroprevalence of T. gondii, as a basis for developing a surveillance system, we studied the long term seroprevalence over years, farming systems and regions, and seasonal patterns of T. gondii seroprevalence in Dutch slaughter pigs. During a five year study period from 2012 to 2016, serum samples were routinely collected in five Dutch pig slaughterhouses. The sera were tested in an ELISA for the presence of antibodies against Toxoplasma. In total 226,340 serum samples were collected and tested during the study period. The observed seroprevalence varied over years, with the highest overall seroprevalence in 2014 (2.8%) and the lowest in 2016 (1.4%). A higher seroprevalence was observed in pigs from organic farms compared to pigs from conventional farms. The overall risk of infection was on average 2.63 times significantly (p < 0.001) higher for organically raised pigs than for conventionally raised pigs. A seasonal pattern in seroprevalence was observed: the results showed a dominant annual periodicity with a seroprevalence peak in winter around week 1 and a minimum seroprevalence in summer around week 27.

To our knowledge, this is the first large scale study on the seroprevalence of T. gondii in slaughter pigs. In comparison to other European serological studies, the observed seroprevalence seems to be relatively low. However, care is needed when comparing the results with other studies because of differences in test setup, the number of samples and time period of sampling. The results can be used as a starting point for developing a surveillance system for T. gondii, and for implementation of intervention measures.

Cross-Sectional Study of Toxoplasma gondii Infection in Pig Farms in England

Ingestion of undercooked meat has been proposed as an important source of human Toxoplasma gondii infection. To ascertain the contribution of meat consumption to the risk of human infection, estimates of the prevalence of infection in meat-producing animals are required. A cross-sectional study was conducted to assess T. gondii infection in pigs raised in England, to identify risk factors for infection, and to compare performance of two serological tests: modified agglutination test (MAT) and enzyme-linked immunosorbent assay (ELISA). Blood samples from 2071 slaughter pigs originating from 131 farms were collected and 75 (3.6%) were found to be positive by MAT. Positive pigs originated from 24 farms. A subset of samples (n = 492) were tested using ELISA, and a significant disagreement (p < 0.001) was found between the two tests. An empirical Bayes approach was used to estimate the farm-level prevalence and the probability of each individual farm having at least one positive animal, considering the uncertainty arising from the sampling strategy and the imperfect test performance. The adjusted farm-level prevalence was 11.5% (95% credible interval of positive farms 8.4-16.0%). Two different criteria were used for classifying farms as infected: (1) ≥50% probability of having at least one infected pig (n = 5, 6.8%) and (2) ≥10% probability (n = 15, 20.5%). Data on putative risk factors were obtained for 73 farms. Using a 10% cutoff, the relative risk (RR) of infection was higher in farms where cats have direct access to pigs' food (RR = 2.6; p = 0.04), pigs have outdoor access (RR = 3.0; p = 0.04), and farms keeping ≤200 pigs (RR = 3.9; p = 0.02), with strong collinearity between the three variables. The findings suggest a low level of T. gondii infection in the farms studied, most of which are likely to send to slaughter batches comprising 100% uninfected pigs. These results provide key inputs to quantitatively assess the T. gondii risk posed by pork to consumers.

Seroprevalence of Toxoplasma gondii and Neospora caninum in slaughtered pigs in the Czech Republic

In the Czech Republic, sera from 551 clinically healthy adult slaughtered pigs (females, 6–8 months old) were collected during the first half of June in 2010. Sera were tested for Toxoplasma gondii-specific IgG antibodies by an enzyme-linked immunosorbent assay; samples with more than 50% S/P were considered as positive. The same samples were also analysed for Neospora caninum antibodies using a commercial competitive-inhibition enzyme-linked immunosorbent assay; samples with more than 30% inhibition were considered as positive. Antibodies against T. gondii were found in 198 pigs (36%) in all districts with prevalences ranging from 18% to 75%. Antibodies against N. caninum were found in 16 pigs (3%); positive animals were found in 4 districts with prevalences ranging from 1% to 20%. Indication of mixed infections (concurrent presence of both N. caninum and T. gondii antibodies) was found in 8 (1·5%) pigs. The results of our study indicate that pigs in the Czech Republic have a relatively high seroprevalence for T. gondii, while they have only a low seroprevalence for N. caninum. Therefore, natural infection with T. gondii seems to be very common in Czech pigs. It is the first evidence of N. caninum antibodies in pigs in the Czech Republic. These results complete data about N. caninum infection in pigs in Europe.

IFN-γ expression and infectivity of Toxoplasma infected tissues are associated with an antibody response against GRA7 in experimentally infected pigs

Toxoplasma gondii, an obligate intracellular parasite, can be transmitted to humans via the consumption of infected meat. However, there are currently no veterinary diagnostic tests available for the screening of animals at slaughter. In the current work, we investigated whether cytokine responses in the blood, and antibody responses against recombinant T. gondii GRA1, GRA7, MIC3 proteins and a chimeric antigen EC2 encoding MIC2-MIC3-SAG1, are associated with the infectivity of porcine tissues after experimental infection with T. gondii. Two weeks after experimental infection of conventional 5-week-old seronegative pigs, an IFN-γ response was detected in the blood, with a kinetic profile that followed the magnitude of the GRA7 antibody response. Antibody responses to GRA1, MIC3 and EC2 were very weak or absent up to 6 weeks post infection. Antibodies against GRA7 occurred in all infected animals and were associated with the presence of the parasite in tissues at euthanasia a few months later, as demonstrated by quantitative real-time PCR and isolation by bio-assay. Remarkably, although brain and heart tissue remained infectious, musculus gastrocnemius and musculus longissimus dorsi were found clear of infectious parasites 6 months after experimental infection. Seropositive response in a GRA7 ELISA indicates a Toxoplasma infection in pigs and is predictive of the presence of infectious cysts in pig heart and brain. This new ELISA is a promising tool to study the prevalence of Toxoplasma infection in pigs. Clearance of the infection in certain pig tissues suggests that the risk assessment of pig meat for human health needs further evaluation.

Age-related Toxoplasma gondii seroprevalence in Dutch wild boar inconsistent with lifelong persistence of antibodies

Toxoplasma gondii is an important zoonotic pathogen that is best known as a cause of abortion or abnormalities in the newborn after primary infection during pregnancy. Our aim was to determine the prevalence of T. gondii in wild boar to investigate the possible role of their meat in human infection and to get an indication of the environmental contamination with T. gondii. The presence of anti-T. gondii antibodies was determined by in-house ELISA in 509 wild boar shot in 2002/2003 and 464 wild boar shot in 2007. Most of the boar originated from the "Roerstreek" (n = 673) or the "Veluwe" (n = 241). A binormal mixture model was fitted to the log-transformed optical density values for wild boar up to 20 months old to estimate the optimal cut-off value (-0.685) and accompanying sensitivity (90.6%) and specificity (93.6%). The overall seroprevalence was estimated at 24.4% (95% CI: 21.1-27.7%). The prevalence did not show variation between sampling years or regions, indicating a stable and homogeneous infection pressure from the environment. The relation between age and seroprevalence was studied in two stages. Firstly, seroprevalence by age group was determined by fitting the binary mixture model to 200 animals per age category. The prevalence showed a steep increase until approximately 10 months of age but stabilized at approximately 35% thereafter. Secondly, we fitted the age-dependent seroprevalence data to several SIR-type models, with seropositives as infected (I) and seronegatives as either susceptible (S) or resistant (R). A model with a recovery rate (SIS) was superior to a model without a recovery rate (SI). This finding is not consistent with the traditional view of lifelong persistence of T. gondii infections. The high seroprevalence suggests that eating undercooked wild boar meat may pose a risk of infection with T. gondii.

Prevalence and risk factors for Toxoplasma gondii infection in certified and non-certified pig breeding farms in the Toledo microregion, PR, Brazil

Toxoplasma gondii infection has been diagnosed in pigs all over the world. Economical losses are generally related to reproductive disorders. Toxoplasma infection is also a matter of public health because tissue cysts of the parasite may remain in pork and pork products, and become sources of human infection. The objective of this study was to evaluate the frequency and risk factors associated with Toxoplasma infection in certified and non-certified pig breeding farms in the Toledo microregion, in the State of Paraná, Brazil which includes the cities of Toledo, Nova Santa Rosa, Sao José das Palmeiras and Sao Pedro do Iguaçu. Relative frequency of infection was 13.4%, independently of the type of farm. Logistic regression analysis showed that the following factors were associated with infection: absence of workers exclusive for each area of the farm, access of other animals to feeders and drinkers, lack of lids in drinkers, lack of rodent control measures, mean piglet number and weight at weaning per female.

Evaluation of IFA, MAT, ELISAs and immunoblotting for the detection of anti-Toxoplasma gondii antibodies in paired serum and aqueous humour samples from experimentally infected pigs

The study evaluated the efficiency of diagnostic laboratory methods to detect anti-Toxoplasma gondii antibodies in paired serum and aqueous humour samples from experimentally infected pigs. 18-mixed breed pigs were used during the experiment; these were divided into two groups, G1 (infected group, n=10) and G2 (uninfected group, n=8). Infection was performed with 4 x 10(4) VEG strain oocysts at day 0 by the oral route in G1 animals. All pigs were euthanized at day 60, when retina, aqueous humour, and blood samples were collected. Anti-T. gondii antibody levels were assessed in serum (s) and aqueous humour (ah) by indirect immunofluorescence assay (IFA), modified agglutination test (MAT), m-ELISA (using crude membranes from T. gondii tachyzoites as antigen) and r-ELISA (using rhoptries from T. gondii tachyzoites as antigen). Polymerase chain reactions (PCR) of samples from the retina were performed by using Tox4 and Tox5 primers. Antibody titers of G1 animals ranged from 128 to 1024 and from 16 to 256 in serum and aqueous humour, respectively. There were differences in the correlation coefficients between IFA(s) x IFA (ah) (r=0.62, P=0.05), MAT(s) x MAT (ah) (r=0.97, P<0.0001); however, there was no significant difference between r-ELISA(s) x r-ELISA (ah) (r= 0.14, P=0.7). Antibodies present in serum and aqueous humour recognized similar antigens. Samples of retina were positive by PCR in 30% (3/10) of infected pigs. G2 animals remained without antibody levels and were PCR negative throughout the experiment. These results suggest that the use of a combination of tests and immunoblotting for paired aqueous humour and serum samples could improve the sensitivity and specificity for the diagnosis of ocular toxoplasmosis.

Evaluation of the indirect fluorescent antibody test and modified agglutination test for detection of antibodies against Toxoplasma gondii in experimentally infected pigs

The study determined the sensitivity and specificity of the indirect fluorescent antibody test (IFAT) and modified agglutination test (MAT) for anti-Toxoplasma gondii antibody detection by analyzing sera from 46 experimentally infected pigs. Values for sensitivity were 95.7% (confidence interval 95%: 84.0-99.2%) and for specificity 97.8% (confidence interval 95%: 87.0-99.9%) in both tests. There was an optimum agreement of results between IFAT and MAT evidenced by a Kappa test of 0.86. These results validate these tests for the detection of T. gondii infection in pigs. IFAT and MAT despite methodologies with different characteristics and readings have similar accuracy in pig serum samples.

Cross-sectional survey in pig breeding farms in Hesse, Germany: seroprevalence and risk factors of infections with Toxoplasma gondii, Sarcocystis spp. and Neospora caninum in sows

A cross-sectional survey was performed to estimate the prevalences of antibodies to Toxoplasma gondii (ELISA, IFAT), Sarcocystis spp. (ELISA, using S. miescheriana as antigen) and Neospora caninum (ELISA, immunoblotting) in sows from breeding farms in southern Hesse, Germany. A total of 2041 plasma samples of sows from 94 randomly selected farms was examined. Data on farm profiles, husbandry management and sows were collected by a questionnaire and exploratively analysed. For T. gondii the ELISA results agreed well with the results obtained by IFAT (kappa=0.71). Antibodies to T. gondii were detected by ELISA in 19% of the sows. Sixty-nine percent of the farms had at least one seropositive sow, and a within-farm seroprevalence of >or=50% was observed in 14% of all farms. The prevalence of anti-T. gondii antibodies was positively correlated with the age of sows. The within-herd seroprevalence was significantly higher in farms with reproductive disorders than in those without such problems. On the farm level, the farm type 'piglet production' (versus 'pedigree breeding' or 'farrow-to-finish') was the only risk factor associated with the presence of T. gondii-seropositive sows. Antibodies to Sarcocystis spp. were found in 29% of the sows. Seventy-two percent of the farms harboured at least one seropositive sow, and a within-farm seroprevalence of >or=50% was detected in 23% of all farms. The seroprevalence increased significantly with the age of sows. On the farm level, only the farm type 'piglet production' (versus 'pedigree breeding') and the replacement of sows by purchasing (versus raising on the own farm) were identified as risk factors for seropositivity. Antibodies to N. caninum were detected in one sow using both the screening ELISA and the confirmatory immunoblotting technique. This may indicate the first natural N. caninum infection in pigs.

Cytokine and lymphocyte profiles in miniature swine after oral infection with Toxoplasma gondii oocysts

Pigs are considered an important source of Toxoplasma gondii infection for humans. A major strategy for immune prophylaxis of toxoplasmosis in swine is the understanding of the immune response against T. gondii infection. The phenotype of peripheral blood mononuclear cells (PBMC) and the kinetics of interferon-gamma (IFN-gamma), interleukin-12 (IL-12) and interleukin-10 (IL-10) transcriptional changes were characterised in miniature swine following infection. A total of 66, 4-9-month-old miniature swine were used for three experiments performed over a period of 2 years. All pigs were fed iota1000 oocysts of the VEG strain of T. gondii and blood samples were obtained on the day of inoculation and at days 3, 6, 10, 17, 25, 32 and 40 after infection. An increase in expression of activation markers CD25 and SLA-DQ was detected in the first week of infection. A significant increase in the percentage of CD8+cells was observed in the second week of infection. Relative competitive RT-PCR analysis indicated an increase in IFN-gamma mRNA as well as a reduction in IL-10 mRNA during the second week post infection. Increase in IL-12 transcription was not observed until the fourth week of infection. The ability of the pigs to respond to T. gondii infection by simultaneously inducing pro-inflammatory cytokines early and anti-inflammatory cytokines later is a likely indication of the requirement to strike a balance between controlling parasite growth and avoiding cytokine toxicity.

The prevalence and avidity of Toxoplasma gondii IgG antibodies in pigs from Brazil and Peru

Raw or inadequately cooked pork is an important source of Toxoplasma gondii infection, and the infection rate in animals used as human food, is an important risk predictor. The prevalence of this infection was estimated in 396 sera from 5-month old pigs obtained at abattoirs in São Paulo, Brazil (300) and Lima, Peru (96). The seroprevalence was higher in pigs from Peru (32.3%) as compared to Brazil (9.6%), as detected by ELISA and Western blot. Hemagglutination gave poor resolution which was not useful for the diagnosis of T. gondii infection. Specific antibody avidity is correlated with infection time, as shown in experimentally infected piglets. Using an arbitrary cut-off of 50% avidity index, Brazilian pigs were found to be more recently infected than Peruvian pigs. Pork should be considered a significant source of human T. gondii infection both in Brazil and Peru. Avidity assays could help in the detection of the time of T. gondii infection in pigs, allowing preventive management.

Toxoplasma gondii recombinant antigens H4 and H11: use in ELISAs for detection of toxoplasmosis in swine

Toxoplasma gondii recombinant antigens H4 and H11 were assessed for their potential for use in ELISA for diagnosis of toxoplasmosis in swine. The antigens were evaluated with sera from young pigs experimentally infected with T. gondii. Results were compared with ELISAs based on a native T. gondii antigen extract. Although recombinant antigen ELISAs showed a sharp rise in response with some sera very early after infection, they were relatively non-reactive with late (chronic) infection sera.