Development and validation of a real-time PCR assay for the detection of Toxoplasma gondii DNA in animal and meat samples

Molecular and serological detection of Toxoplasma gondii infection in mammals in the Taipei Zoo

Toxoplasmosis caused by Toxoplasma gondii affects both conservation and public health efforts. In the Taipei Zoo, toxoplasmosis was diagnosed in ring-tailed lemurs and a meerkat in 2019 while a freeze-thaw meat strategy had been applied to carnivores before the event. To investigate the possible risk factors associated with T. gondii infection in the Taipei Zoo, 179 veterinary visiting mammals from 2019-2021 and six stray cats were included to detect anti-T. gondii IgG and IgM in their serum via ELISA, and T. gondii in their faeces and blood via PCR. Although the overall T. gondii IgG seroprevalence was 33.5% and PCR positivity was 16.2% in the zoo mammals, the correlation between T. gondii PCR and systemic IgG results was low. An omnivorous diet (adjusted OR = 0.4; 95% CI: 0.2-1.0), a herbivorous diet (adjusted OR = 3.2; 95% CI: 1.1-9.6), and animals in the Conservation Area where stray cats appeared (adjusted OR = 18.3; 95% CI: 3.9-85.9) were independent risk factors for T. gondii infection. The low T. gondii-specific IgM positivity (0.6%) suggests that most animals did not have acute T. gondii infection. In conclusion, our findings indirectly support that feeding frozen meat to carnivores, cleaning fresh food, and restricting access to stray cats to prevent faecal contaminants could prevent animals from T. gondii exposure.

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.

Tamoxifen Increased Parasite Burden and Induced a Series of Histopathological and Immunohistochemical Changes During Chronic Toxoplasmosis in Experimentally Infected Mice

The global distribution of breast cancer and the opportunistic nature of the parasite have resulted in many patients with breast cancer becoming infected with toxoplasmosis. However, very limited information is available about the potential effects of tamoxifen on chronic toxoplasmosis and its contribution to the reactivation of the latent infection. The present study investigated the potential effects of tamoxifen on chronic toxoplasmosis in animal models (Swiss albino mice). Following induction of chronic toxoplasmosis and treatment with the drug for 14 and 28 days, the anti-parasitic effects of tamoxifen were evaluated by parasitological assessment and counting of Toxoplasma cysts. In addition, the effects of the drug on the parasite load were evaluated and quantitated using TaqMan real-time quantitative PCR followed by investigation of the major histopathological changes and immunohistochemical findings. Interestingly, tamoxifen increased the parasite burden on animals treated with the drug during 14 and 28 days as compared with the control group. The quantification of the DNA concentrations of Toxoplasma P29 gene after the treatment with the drug revealed a higher parasite load in both treated groups vs. control groups. Furthermore, treatment with tamoxifen induced a series of histopathological and immunohistochemical changes in the kidney, liver, brain, and uterus, revealing the exacerbating effect of tamoxifen against chronic toxoplasmosis. These changes were represented by the presence of multiple T. gondii tissue cysts in the lumen of proximal convoluted tubules associated with complete necrosis in their lining epithelium of the kidney section. Meanwhile, liver tissue revealed multiple T. gondii tissue cysts in hepatic parenchyma which altered the structure of hepatocytes. Moreover, clusters of intracellular tachyzoites were observed in the lining epithelium of endometrium associated with severe endometrial necrosis and appeared as diffuse nuclear pyknosis combined with sever mononuclear cellular infiltration. Brain tissues experienced the presence of hemorrhages in pia mater and multiple T. gondii tissue cysts in brain tissue. The severity of the lesions was maximized by increasing the duration of treatment. Collectively, the study concluded novel findings in relation to the potential role of tamoxifen during chronic toxoplasmosis. These findings are very important for combating the disease, particularly in immunocompromised patients which could be life-threatening.

Absolute quantification of E. coli virulence and housekeeping genes to determine pathogen loads in enumerated environmental samples

Quantifying pathogenic genes with q-PCR in complex samples to determine the pathogen loads is influenced by a wide range of factors, including choice of extraction method, standard curve, and the decision to use relative versus absolute quantification of the genes. The aim was to investigate the standardisation of q-PCR methods to determine enumerated E. coli gene ratios grown with the IDEXX Colilert^® Quanti-Trays^® using enteropathogenic E. coli as the model pathogen. q-PCR targeting the eaeA and gadAB genes was used to calculate the eaeA: gadAB ratios for clinical strains collected between [2005–2006 (n = 55)] and [2008–2009 (n = 19)] using the LinRegPCR software and Corbett Research Thermal cycler software. Both programs grouped the isolates into two distinct groups based on the gene ratios although the Corbett Research Thermal cycler software gave results one log higher than the LinRegPCR program. Although the eaeA: gadAB ratio range was determined using extracted E. coli DNA, the impact of free DNA and other bacteria present in the sample needed to be understood. Standard curve variations using serially diluted extracted E. coli DNA, serially diluted pure E. coli culture followed by DNA extraction from each dilution with or without other bacteria was tested using the eaeA q-PCR to quantify the genes. Comparison of the standard curves showed no significant difference between standard curves prepared with diluted DNA or with cells diluted before the DNA is extracted (P = 0.435). Significant differences were observed when background DNA was included in the diluent or Coliform cells added to the diluent to dilute cells before the DNA is extracted (P < 0.001). The “carrier” DNA and Coliform cells enhanced the DNA extraction results resulting in better PCR efficiency. This will have an influence on the quantification of gene ratios and pathogen load in samples containing lower numbers of E. coli.

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.

Potential Risk of Three Zoonotic Protozoa (Cryptosporidium spp., Giardia duodenalis, and Toxoplasma gondii) Transmission from Fish Consumption

In recent decades, worldwide fish consumption has increased notably worldwide. Despite the health benefits of fish consumption, it also can suppose a risk because of fishborne diseases, including parasitic infections. Global changes are leading to the emergence of parasites in new locations and to the appearance of new sources of transmission. That is the case of the zoonotic protozoa Cryptosporidium spp., Giardia duodenalis, and Toxoplasma gondii; all of them reach aquatic environments and have been found in shellfish. Similarly, these protozoa can be present in other aquatic animals, such as fish. The present review gives an overview on these three zoonotic protozoa in order to understand their potential presence in fish and to comprehensively revise all the evidences of fish as a new potential source of Cryptosporidium spp., Giardia duodenalis, and Toxoplasma gondii transmission. All of them have been found in both marine and freshwater fishes. Until now, it has not been possible to demonstrate that fish are natural hosts for these protozoa; otherwise, they would merely act as mechanical transporters. Nevertheless, even if fish only accumulate and transport these protozoa, they could be a "new" source of infection for people.

Seroepidemiology of Toxoplasma gondii in Dairy Cows in Southeastern Brazil: Seropositive Cows on All Farms Investigated

PURPOSE

This study aimed to estimate the prevalence and identify the risk factors associated with the higher in-herd T. gondii seroprevalence in dairy cows in 37 farms in southern Minas Gerais, Southeastern Brazil.

METHODS

Serum samples from 1,105 dairy cows were subjected to an indirect fluorescence antibody test (IFAT 1:64) for anti-T. gondii IgG. The association existing between possible risk factors at the herd level and the seroprevalence were verified through Generalized Estimating Equation (GEE) multiple logistic regression models.

RESULTS

Anti-T. gondii antibodies were observed in 31.4% of the cows (347; 95% CI= 28.7-34.2) and on 100% of the farms (37; 95% CI= 90.6-100.0%), indicating that all properties possessed at least one seropositive animal. For univariate analysis, herds with seroprevalence were categorized as greater and less than 30% as the outcome. The "breeding of Holstein Friesian cows" (p= 0.016, OR= 6.667, 95% CI= 1.500-29.628) and in an "intensive system" (p= 0.013, OR= 6.120, 95% CI= 1.394-26.876) increased the chance of the herd seroprevalence being greater than 30% by approximately six-fold. However, these variables did not exhibit a significant association (p >0.05) in the Generalized Estimating Equations (GEE) logistic regression model.

CONCLUSIONS

The results demonstrate that T. gondii infection is widespread among dairy cows in the south of Minas Gerais, with a wide environmental dispersion of the parasite on farms in this region.

A new strain of Toxoplasma gondii circulating in southern Brazil

Recently, an outbreak of human toxoplasmosis was identified in Santa Maria city, Southern Brazil. However, the suspected vehicle of Toxoplasma gondii contamination in this region remains unclear. This study was conduct to analyze whether pork meat samples collected in supermarkets from Santa Maria city, RS, could be infected with T. gondii. Thus, we analyzed the presence of T. gondii DNA in 20 pork hearts, 20 pork tongues and 20 sausages. DNA was extracted from each sample and real-time PCR was performed using 529-bp and B1 markers. T. gondii genotyping was performed by PCR-RFLP analysis. T. gondii DNA was detected in 2 of 20 (10%) heart samples and in 1 of 20 (5%) tongue samples using 529-bp marker. Besides, those 2 (10%) heart samples also were positive for T. gondii using B1 marker. All sausage samples were negative for both markers. Genotyping revealed a new atypical genotype in the pork meat. Our findings were not able to confirm whether these food samples were involved in some outbreak. However, we can conclude that food samples containing T. gondii can be displayed in Santa Maria supermarkets. In addition, a new T. gondii genotype was identified circulating in southern Brazil.

Toxoplasma gondii in edible fishes captured in the Mediterranean basin

The issue of whether market fish can be involved in the transmission of Toxoplasma gondii in the marine environment is highly debated since toxoplasmosis has been diagnosed frequently in cetaceans stranded along the Mediterranean coastlines in recent times. To support the hypothesis that fishes can harbour and effectively transmit the parasite to top-of-the-food-chain marine organisms and to human consumers of fishery products, a total of 1,293 fishes from 17 species obtained from wholesale and local fish markets were examined for T. gondii DNA. Real-time PCR was performed in samples obtained by separately pooling intestines, gills and skin/muscles collected from each fish species. Thirty-two out of 147 pooled samples from 12 different fish species were found contaminated with T. gondii DNA that was detected in 16 samples of skin/muscle and in 11 samples of both intestine and gills. Quantitative analysis of amplified DNA performed by both real-time PCR and digital PCR (dPCR) confirmed that positive fish samples were contaminated with Toxoplasma genomic DNA to an extent of 6.10 × 10^-2 to 2.77 × 10⁴  copies/ml (quantitative PCR) and of 1 to 5.7 × 10⁴  copies/ml (dPCR). Fishes are not considered competent biological hosts for T. gondii; nonetheless, they can be contaminated with T. gondii oocysts flowing via freshwater run-offs (untreated sewage discharges, soil flooding) into the marine environment, thus acting as mechanical carriers. Although the detection of viable and infective T. gondii oocysts was not the objective of this investigation, the results here reported suggest that fish species sold for human consumption can be accidentally involved in the transmission route of the parasite in the marine environment and that the risk of foodborne transmission of toxoplasmosis to fish consumers should be further investigated.