Methods to assess the effect of meat processing on viability of Toxoplasma gondii: towards replacement of mouse bioassay by in vitro testing

Toxoplasma gondii infection in European brown hares (Lepus europaeus) in Brazil

Toxoplasmosis is a worldwide zoonosis that affects warm-blooded animals, including humans. Wild animals can act as intermediate hosts of this pathogen; thus, this study aims to detect Toxoplasma gondii infection in invasive European brown hares in Brazil. For this, 72 wild European brown hares were captured from July 2020 to June 2022 in three Brazilian states: São Paulo, Paraná, and Rio Grande do Sul. The diagnostic of Toxoplasma gondii infection was performed by bioassay in mouse, histopathology in Hematoxylin-Eosin-stained tissue sections (brain, liver, lungs, kidneys, and small intestine), serology by IFAT, and molecular techniques by conventional PCR and qPCR. The combined prevalence of the different diagnostic methods was 51.4% (37/72, CI= 40.1 - 62.6 %), and there was no statistical difference between sexes, age range, or geographical region of the hosts. Mouse bioassay was the technique that detected more positive hares. To our knowledge, this is the first confirmation of Toxoplasma gondii infection in invasive European brown hares in Brazil. These animals act as reservoirs and potential infection source for carnivores and other wild and domestic animals, including humans, thus contributing to perpetuate the disease cycle in São Paulo, Paraná, and Rio Grande do Sul States. Research such as the present study is necessary to raise awareness about the role of animals in the disease cycle.

In vitro assay to determine inactivation of Toxoplasma gondii in meat samples

Consumption of raw and undercooked meat is considered as an important source of Toxoplasma gondii infections. However, most non-heated meat products contain salt and additives, which affect T. gondii viability. It was our aim to develop an in vitro method to substitute the mouse bioassay for determining the effect of salting on T. gondii viability. Two sheep were experimentally infected by oral inoculation with 6.5 × 104 oocysts. Grinded meat samples of 50 g were prepared from heart, diaphragm, and four meat cuts. Also, pooled meat samples were either kept untreated (positive control), frozen (negative control) or supplemented with 0.6 %, 0.9 %, 1.2 % or 2.7 % NaCl. All samples were digested in pepsin-HCl solution, and digests were inoculated in duplicate onto monolayers of RK13 (a rabbit kidney cell line). Cells were maintained for up to four weeks and parasite growth was monitored by assessing Cq-values using the T. gondii qPCR on cell culture supernatant in intervals of one week and ΔCq-values determined. Additionally, 500 μL of each digest from the individual meat cuts, heart and diaphragm were inoculated in duplicate in IFNγ KO mice. Both sheep developed an antibody response and tissue samples contained similar concentrations of T. gondii DNA. From all untreated meat samples positive ΔCq-values were obtained in the in vitro assay, indicating presence and multiplication of viable parasites. This was in line with the mouse bioassay, with the exception of a negative mouse bioassay on one heart sample. Samples supplemented with 0.6 %-1.2 % NaCl showed positive ΔCq-values over time. The frozen sample and the sample supplemented with 2.7 % NaCl remained qPCR positive but with high Cq-values, which indicated no growth. In conclusion, the in vitro method has successfully been used to detect viable T. gondii in tissues of experimentally infected sheep, and a clear difference in T. gondii viability was observed between the samples supplemented with 2.7 % NaCl and those with 1.2 % NaCl or less.

Global prevalence of Toxoplasma gondii in birds: A systematic review and meta-analysis

Among the potential animal reservoirs of the zoonotic parasite T. gondii, birds have received relatively little attention. This systematic review and meta-analysis aimed to assess the global status and to provide an overview of the epidemiology of T. gondii infection in birds. The standard protocol of preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were followed. Scopus, PubMed, Web of Science, Science Direct, ProQuest, and Google Scholar were searched for relevant publications from January 1990, to March 2024. All peer-reviewed original research articles describing the prevalence of T. gondii in birds were included. Inclusion and exclusion criteria were applied, and both direct and indirect detection were considered. The point estimates and 95% confidence intervals were calculated using the meta-package in R (version 3.6.1). The variance between studies (heterogeneity) was quantified by the I2 index. Finally, 258 articles (including 380 datasets) were eligible for inclusion in the systematic review and meta-analysis. The global pooled prevalence was 24% (21 - 26%). The highest prevalence of T. gondii was observed in buzzards (52%, 34 - 70%), turkeys (31%, 17 - 46%), and chickens (30%, 26 - 34%). The present study provides a comprehensive view of the global prevalence of T. gondii in birds.

Isolation of Toxoplasma gondii in cell culture: an alternative to bioassay

Toxoplasma gondii is an apicomplexan protozoan parasite that can infect mammals and birds. The infection can cause acute toxoplasmosis and death in susceptible hosts. Bioassay using cats and mice has been the standard for the isolation of T. gondii from infected hosts for the past several decades. However, bioassay is labor-intensive, expensive, and involves using laboratory animals. To search alternative approaches and o work towards replacement of animal experiments, we summarized the key literature and conducted four experiments to isolate T. gondii in vitro by cell culture. A few heart tissue samples from animals with the highest antibody titers in a given collection were used for T. gondii isolation. These experiments included samples from five out of 51 wild ducks, four of 46 wild turkeys, six of 24 white-tailed deer, as well as from six kangaroos that had died with acute toxoplasmosis in a zoo. These experiments resulted in three isolates from five chronically infected wild ducks (60%), four isolates from four chronically infected wild turkeys (100%), one isolate from six chronically infected white-tailed deer (17%), and four isolates from six kangaroos with acute toxoplasmosis (67%). In addition, five isolates from the five chronically infected wild ducks were obtained by bioassay in mice, showing a 100% success rate, which is higher than the 60% rate by direct cell culture. These T. gondii isolates were successfully propagated in human foreskin fibroblast (HFF) or Vero cells, and genotyped by multilocus PCR-RFLP markers. The results showed that it is practical to isolate T. gondii directly in cell culture. Although the cell culture approach may not be as sensitive as the bioassay, it does provide an alternative that is simple, cost-effective, ethically more acceptable, and less time-sensitive to isolate T. gondii. In this paper we propose a procedure that may be applied and further optimized for isolation of T. gondii.

Molecular detection and viability discrimination of zoonotic protozoan pathogens in oysters and seawater

The presence of foodborne protozoan pathogens including Cryptosporidium parvum, Giardia duodenalis, Toxoplasma gondii, and Cyclospora cayetanensis in commercial shellfish has been reported across diverse geographical regions. In the present study, a novel multiplex nested polymerase chain reaction (PCR) assay was validated to simultaneously detect and discriminate these four targeted parasites in oyster tissues including whole tissue homogenate, digestive gland, gills, and hemolymph, as well as seawater where shellfish grow. To differentiate viable and non-viable protozoan (oo)cysts, we further evaluated reverse transcription quantitative PCR (RT-qPCR) assays through systematic laboratory spiking experiments by spiking not only dilutions of viable parasites but also mixtures of viable and non-viable parasites in the oyster tissues and seawater. Results demonstrate that multiplex PCR can detect as few as 5-10 (oo)cysts in at least one oyster matrix, as well as in 10 L of seawater. All parasites were detected at the lowest spiking dilution (5 (oo)cysts per extract) in hemolymph, however the probability of detection varied across the difference matrices tested for each parasite. RT-qPCR further discriminated viable from non-viable (heat-inactivated) C. parvum and T. gondii in seawater and hemolymph but did not perform well in other oyster matrices. This systematic spiking study demonstrates that a molecular approach combining multiplex PCR for sensitive and affordable screening of protozoan DNA and subsequent RT-qPCR assay for viability discrimination presents an important advance for accurately determining the risk of protozoal illness in humans due to consumption of contaminated shellfish.

Molecular Detection of Toxoplasma gondii in Blood Samples of Domestic Livestock in the Republic of Korea

Toxoplasma gondii, a major zoonotic pathogen distributed worldwide, causes severe infections in humans, animals, and birds. However, limited information is available regarding T. gondii infection in livestock in the Republic of Korea (ROK). Herein, we determined the prevalence of T. gondii infection in livestock in the ROK and identified animal species that can potentially transmit T. gondii to humans. B1 gene-targeting nested polymerase chain reaction detected T. gondii DNA in 3.3% (2/61), 2.9% (3/105), 14.1% (11/78), and 15.4% (14/91) of dairy cattle, beef cattle, Boer goats, and Korean native goats, respectively. The prevalence of T. gondii was significantly higher (p = 0.002) in goats than in cattle. The risk of contracting T. gondii infection was significantly higher by 6.18-fold in Korean native goats (95% confidence interval [CI]: 1.72–22.27%, p = 0.005) and by 5.58-fold in Boer goats (95% CI: 1.50–20.76%, p = 0.010) than in beef cattle. Our T. gondii DNA sequences exhibited 97.1–100% homology with those obtained from various hosts in other countries. To the best of our knowledge, this is the first study to report T. gondii infection using the blood samples of domestic ruminants in the ROK. The results revealed that the prevalence of T. gondii infection is higher in goats than in cattle as determined by molecular detection. Thus, these findings suggest that T. gondii can be transmitted from ruminants to humans via meat consumption.

Foodborne Parasites and Their Complex Life Cycles Challenging Food Safety in Different Food Chains

Zoonotic foodborne parasites often represent complex, multi host life cycles with parasite stages in the hosts, but also in the environment. This manuscript aims to provide an overview of important zoonotic foodborne parasites, with a focus on the different food chains in which parasite stages may occur. We have chosen some examples of meat-borne parasites occurring in livestock (Taenia spp., Trichinella spp. and Toxoplasma gondii), as well as Fasciola spp., an example of a zoonotic parasite of livestock, but transmitted to humans via contaminated vegetables or water, covering the 'farm to fork' food chain; and meat-borne parasites occurring in wildlife (Trichinella spp., Toxoplasma gondii), covering the 'forest to fork' food chain. Moreover, fish-borne parasites (Clonorchis spp., Opisthorchis spp. and Anisakidae) covering the 'pond/ocean/freshwater to fork' food chain are reviewed. The increased popularity of consumption of raw and ready-to-eat meat, fish and vegetables may pose a risk for consumers, since most post-harvest processing measures do not always guarantee the complete removal of parasite stages or their effective inactivation. We also highlight the impact of increasing contact between wildlife, livestock and humans on food safety. Risk based approaches, and diagnostics and control/prevention tackled from an integrated, multipathogen and multidisciplinary point of view should be considered as well.

Toxoplasma gondii in Foods: Prevalence, Control, and Safety

Toxoplasma gondii is an obligate intracellular parasite that causes toxoplasmosis, with approximately one third of the population around the world seropositive. The consumption of contaminated food is the main source of infection. These include meat products with T. gondii tissue cysts, and dairy products with tachyzoites. Recently, contamination has been detected in fresh products with oocysts and marine products. Despite the great health problems that are caused by T. gondii, currently there are no standardized methods for its detection in the food industry. In this review, we analyze the current detection methods, the prevalence of T. gondii in different food products, and the control measures. The main detection methods are bioassays, cell culture, molecular and microscopic techniques, and serological methods, but some of these do not have applicability in the food industry. As a result, emerging techniques are being developed that are aimed at the detection of multiple parasites simultaneously that would make their application more efficient in the industry. Since the prevalence of this parasite is high in many products (meat and milk, marine products, and vegetables), it is necessary to standardize detection methods, as well as implement control measures.

Zoonotic Pathogens in Eurasian Beavers (Castor fiber) in the Netherlands

Successful repopulation programs of Eurasian beavers (Castor fiber) have resulted in an increase in beaver populations throughout Europe. This may be of public health relevance because beavers can host multiple zoonotic pathogens. From March 2018 to March 2020, opportunistic testing of dead beavers was performed for hepatitis E virus, orthohantavirus, Anaplasma phagocytophilum, Bartonella spp., extended-spectrum-betalactamase or AmpC (ESBL/AmpC-)-producing Enterobacteriaceae, Francisella tularensis, Leptospira spp., Neoehrlichia mikurensis, Babesia spp., Echinococcus multilocularis, Toxoplasma gondii, and Trichinella spp. From the 24 beavers collected, three zoonotic pathogens were detected. One beaver was positive for T. gondii, one was positive for ESBL/AmpC-producing Enterobacteriaceae, and one was positive for N. mikurensis. The latter finding indicates that beavers can be bitten by Ixodes ricinus and be exposed to tick-borne pathogens. The detected ESBL/AmpC-gene was blaCMY-2 in an Escherichia coli ST6599. The findings suggest that the role of beavers in the spread of zoonotic diseases in the Netherlands is currently limited.

Development of a droplet digital polymerase chain reaction tool for the detection of Toxoplasma gondii in meat samples

Toxoplasmosis is a zoonotic disease caused by the protozoan parasite Toxoplasma gondii. Infection in humans has usually been related to the consumption of raw, undercooked or cured meat. The aim of this study was to develop a droplet digital polymerase chain reaction (ddPCR)-based assay for the detection and quantification of T. gondii in meat samples. To optimize the ddPCR, T.gondii reference DNA aliquots at five known concentrations: 8000 cg/µl, 800 cg/µl, 80 cg/µl, 8 cg/µl were used. Moreover, results obtained by ddPCR and quantitative PCR (qPCR) were compared using 80 known samples (40 positive and 40 negative), as well as 171 unknown diaphragm tissue samples collected at slaughterhouses. The ddPCR showed a sensitivity of 97.5% and a specificity of 100%, with a detection limit of 8 genomic copy/µl of T. gondii. A nearly perfect agreement (κ = 0.85) was found between results obtained by ddPCR and qPCR for both positive and negative known samples analysed. On the 171 diaphragm tissue samples from field, 7.6% resulted positive by ddPCR and only 1.2% by qPCR. Therefore, this innovative method could be very useful for the detection of T. gondii in meat samples, aiming to prevent human infections.

Seroprevalence and risk factors of Toxoplasma gondii in cattle from Unai, Minas Gerais state, Brazil

Toxoplasma gondii is a widespread protozoan parasite that causes infections in animals and humans. The presence of tissue cysts in cattle musculature evidences their epidemiological significance in transmission to humans. The present study aimed to evaluate the seroprevalence of and risk factors of T. gondii seropositivity in beef cattle in the municipality of Unaí, Minas Gerais state, Brazil. Bovine blood samples (n = 612) were collected from 31 herds. Risk factors associated with the animal-level and herd-level seroprevalence were analysed using a questionnaire that investigates the epidemiological aspects of toxoplasmosis. A search for anti-T. gondii antibodies was performed by means of an indirect fluorescent antibody test (IFAT). Analysis of 612 samples showed 369 animals positive for anti-T. gondii antibodies (IFAT ≥64), with a seroprevalence of 60.29% (95% confidence interval (CI): 56.35-64.10). The herd-level seroprevalence was 96.77% (95% CI: 79.00-99.58). Applying a multivariate logistic regression analysis, a test of the association between seroprevalence of T. gondii infection and the potential predictors showed that cats (domestic or wild) with access to the drinking water of cattle were a significant (P = 0.001) predictor. The seroprevalence of T. gondii in cattle destined for human consumption is widely distributed throughout the entire study area. Thus, integrated control measures and strategies are suggested to prevent T. gondii infection in cattle.

High prevalence of anti-Toxoplasma gondii antibodies in beef cattle in Midwestern Brazil

The present study aimed to determine the seroprevalence of anti-Toxoplasma gondii antibodies using an indirect immunofluorescence assay (IFA-IgG) in 3,814 cows aged ≥ 24 months belonging to 353 beef farms in the Mato Grosso state. Additionally, we aimed to identify the possible risk factors associated with seropositivity in Mato Grosso, which encompasses three biomes (Amazon, Cerrado, and Pantanal) of Brazil. Analysis of 3,814 samples observed that 1,307 animals were positive for anti-T. gondii antibodies (IFA-IgG ≥ 64), with an animal-level seroprevalence of 34.27%. Herd-level seroprevalence was 92.07%. In the animal-level model, cows raised in the Amazon and Pantanal biomes and breed studies on European and Zebu or hybrid were found to be at risk for T. gondii seropositivity. Prevalence of anti-T. gondii antibodies in cows destined for human consumption was found to be widely distributed throughout the entire study area. Further studies are required to assess the impact of beef in the possible transmission of toxoplasmosis to humans residing in the region and establish additional control measures for this protozoan mainly on beef herds raised in the Amazon and Pantanal biomes, where the highest values of seroprevalence were observed.

Quantification of viable protozoan parasites on leafy greens using molecular methods

Protozoan contamination in produce is of growing importance due to their capacity to cause illnesses in consumers of fresh leafy greens. Viability assays are essential to accurately estimate health risk caused by viable parasites that contaminate food. We evaluated the efficacy of reverse transcription quantitative PCR (RT-qPCR), propidium monoazide coupled with (q)PCR, and viability staining using propidium iodide through systematic laboratory spiking experiments for selective detection of viable Cryptosporidium parvum, Giardia enterica, and Toxoplasma gondii. In the presence of only viable protozoa, the RT-qPCR assays could accurately detect two to nine (oo)cysts/g spinach (in 10 g processed). When different proportions of viable and inactivated parasite were spiked, mRNA concentrations correlated with increasing proportions of viable (oo)cysts, although low levels of false-positive mRNA signals were detectable in the presence of high amounts of inactivated protozoa. Our study demonstrated that among the methods tested, RT-qPCR performed more effectively to discriminate viable from inactivated C. parvum, G. enterica and T. gondii on spinach. This application of viability methods on leafy greens can be adopted by the produce industry and regulatory agencies charged with protection of human public health to screen leafy greens for the presence of viable protozoan pathogen contamination.

Foodborne transmission of Toxoplasma gondii infection in the last decade. An overview

Toxoplasmosis is a zoonotic disease of global distribution and importance. It is caused by the protozoan parasite Toxoplasma gondii, the only species in the Toxoplasma genus. This parasite can infect most warm-blooded animals, including humans and livestock. Main routes of transmission are by ingestion of tissue cysts in raw or undercooked meat of infected animals, ingestion of raw vegetables or water contaminated with T. gondii oocysts from cat feces, and transplacental. Around one-third of human beings are chronically infected with T. gondii. Most infections appear to be asymptomatic in immunocompetent persons, but toxoplasmosis can be fatal to the fetus and immunocompromised adults. Water and foodborne outbreaks have been caused by this parasite worldwide, but few are well documented. Importantly, T. gondii is a parasite of high importance in animal health, causing reproductive failure, particularly in small ruminants, and clinical toxoplasmosis in many species. This overview discusses the knowledge of T. gondii infections in the last decade focusing on the foodborne transmission of this parasite.