First report of Tunisian coastal water contamination by protozoan parasites using mollusk bivalves as biological indicators

First application of a droplet digital PCR to detect Toxoplasma gondii in mussels

Toxoplasmosis, caused by the protozoan Toxoplasma gondii, is one of the main food-, water- and soil-borne zoonotic disease worldwide. Over the past 20 years many papers were published on the transmission of T. gondii by marine animals, including mollusks, which can concentrate the oocysts and release them. Sporulated oocysts may remain viable and infective for 18 months in seawater. Therefore, raw or undercooked bivalve mollusks pose a risk to humans. This study aimed to apply and validate for the first time a very sensitive digital droplet polymerase chain reaction (ddPCR) protocol to detect and quantify T. gondii DNA in mussels. Four concentration levels: 8000 genomic copies (gc)/μL, 800 gc/μL, 80 gc/μL, 8 gc/μL of a T. gondii reference DNA were tested. DNA was extracted from 80 pools of mussels (Mytilus galloprovincialis). Forty pools were contaminated with T. gondii reference DNA and used as positive controls, while 40 pools were used as negative controls. DdPCR reaction was prepared using a protocol, previously developed by the authors, for detection of T. gondii in meat. Amplification was obtained up 8 gc/μL. All infected replicates resulted positive, as well as no droplets were detected in negative controls. The droplets produced in the reaction ranged from 8,828 to 14,075 (average 12,627 droplets). The sensitivity and specificity of ddPCR were 100% (95%CI = 94.3-99.9). In addition, 100 pools of mussels collected in the Gulf of Naples were used to validate the protocol. Of these 16% were positive (95% CI = 9.7-25.0) for T. gondii. Samples were also tested by real-time PCR and no positive samples were found. Data obtained from ddPCR showed good identification of negative and positive samples with higher specificity and efficiency than real-time PCR. This tool could be very useful for a rapid sensitive detection of low DNA concentrations of T. gondii in mussels, reducing the risk of toxoplasmosis in humans.

Foodborne protozoan parasites in fresh mussels and oysters purchased at retail in Canada

Studies worldwide have reported the presence of protozoan parasites in a variety of commercial bivalve shellfish. The uptake of these parasites by shellfish occurs during filter feeding in faecally-contaminated waters. The objective of the present study was to determine the prevalence of Giardia, Cryptosporidium and Toxoplasma in fresh, live shellfish purchased in three Canadian provinces as part of the retail surveillance activities led by FoodNet Canada (Public Health Agency of Canada). Packages containing mussels (n = 253) or oysters (n = 130) were purchased at grocery stores in FoodNet Canada sentinel sites on a biweekly basis throughout 2018 and 2019, and shipped in coolers to Health Canada for testing. A small number of packages were not tested due to insufficient quantity or poor quality. Following DNA extraction from homogenized, pooled tissues, nested PCR and DNA sequencing were used to detect parasite-specific sequences. Epifluorescence microscopy was used to confirm the presence of intact cysts and oocysts in sequence-confirmed PCR-positive samples. Giardia duodenalis DNA was present in 2.4 % of 247 packages of mussels and 4.0 % of 125 packages of oysters, while Cryptosporidium parvum DNA was present in 5.3 % of 247 packages of mussels and 7.2 % of 125 packages of oysters. Toxoplasma gondii DNA was only found in mussels in 2018 (1.6 % of 249 packages). Parasite DNA was detected in shellfish purchased in all three Canadian provinces sampled, and there was no apparent seasonal variation in prevalence. While the present study did not test for viability, parasites are known to survive for long periods in the marine environment, and these findings suggest that there is a risk of infection, especially when shellfish are consumed raw.

Cyclospora cayetanensis Infection in Developed Countries: Potential Endemic Foci?

Cyclospora cayetanensis infection has emerged as a significant public health concern worldwide. Developed countries are generally considered non-endemic for infection. However, sporadic cases and non-travel-related outbreaks of C. cayetanensis infections associated with domestically grown produce are becoming more common in developed countries. Cyclospora cayetanensis has been detected in fresh produce, surface water, wastewater, irrigation water, and soil in these countries, suggesting that the parasite may be more common in areas with advanced sanitation than previously thought and illustrating the potential risk for exposure and indigenous/autochthonous infections. The evidence suggests the possibility of foci of endemicity in developed countries, particularly in communities where sanitary conditions are compromised, and raises transmission issues that require further research to better define the risks for infection, how widespread C. cayetanensis may be in these areas, and to guide interventions against this infection. The main purpose of the present opinion was to evaluate the presence of cyclosporiasis in developed countries, which is a very important and ongoing issue in food safety.

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.

Occurrence of the protozoan parasites Toxoplasma gondii and Cyclospora cayetanensis in the invasive Atlantic blue crab Callinectes sapidus from the Lesina Lagoon (SE Italy)

The occurrence of the protozoan parasites Toxoplasma gondii and Cyclospora cayetanensis was molecularly investigated in the hemolymph, gills, stomach, hepatopancreas and gonads of the eleven invasive Atlantic blue crab Callinectes sapidus from the Lesina Lagoon (Mediterranean Sea). Out of 11 blue crabs, 6 (54.5%) and 4 (36.4%) were found positive to T. gondii and C. cayetanenis, respectively; parasites were found only in the six females analysed, while the remaining five males resulted negative. Moreover, out of 55 tissues samples, 7 (12.7%) and 8 (14.5%) were positive to T. gondii and C. cayetanensis, respectively with hemolymph and gills being the most infected tissues. This is the first report of the presence of protozoan pathogens in wild crab species collected from a Mediterranean lagoon. The present results may provide a baseline reference on microbial infection in the species for invaded Mediterranean waters, and on the potential health risks related with its consumption if eaten raw.

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.

Contamination of Soil, Water, Fresh Produce, and Bivalve Mollusks with Toxoplasma gondii Oocysts: A Systematic Review

Toxoplasma gondii is a major foodborne pathogen capable of infecting all warm-blooded animals, including humans. Although oocyst-associated toxoplasmosis outbreaks have been documented, the relevance of the environmental transmission route remains poorly investigated. Thus, we carried out an extensive systematic review on T. gondii oocyst contamination of soil, water, fresh produce, and mollusk bivalves, following the PRISMA guidelines. Studies published up to the end of 2020 were searched for in public databases and screened. The reference sections of the selected articles were examined to identify additional studies. A total of 102 out of 3201 articles were selected: 34 articles focused on soil, 40 focused on water, 23 focused on fresh produce (vegetables/fruits), and 21 focused on bivalve mollusks. Toxoplasma gondii oocysts were found in all matrices worldwide, with detection rates ranging from 0.09% (1/1109) to 100% (8/8) using bioassay or PCR-based detection methods. There was a high heterogeneity (I2 = 98.9%), which was influenced by both the sampling strategy (e.g., sampling site and sample type, sample composition, sample origin, season, number of samples, cat presence) and methodology (recovery and detection methods). Harmonized approaches are needed for the detection of T. gondii in different environmental matrices in order to obtain robust and comparable results.

A review of Cyclospora cayetanensis in animals

Cyclosporiasis is a global, emerging disease in humans caused by Cyclospora cayetanensis. The role of animals in the epidemiology of cyclosporiasis is not fully understood. We conducted a narrative review of the published literature on C. cayetanensis in animals. MEDLINE® (Web of Science™ ), Agricola (ProQuest), CABI Global Health (1979 to December 2020) and Food Science and Technology Abstracts (EBSCOhost) (1979 to February 2020) were searched. Studies of C. cayetanensis in or on any species of animal were eligible. Thirteen relevant studies were found. C. cayetanensis was found in wild and farmed Mediterranean mussels (Mytilus galloprovincialis), wild grooved carpet shell clams (Ruditapes decussatus) and in the faeces of dogs (domestic and street), wild chickens, wild rhesus macaques (Macaca mulatta), chimpanzees (Pan troglodytes) from a wildlife research centre, and Cynomolgus monkeys (Macaca fascicularis) from an experimental primate research centre. As the small intestines of the naturally exposed animals were not biopsied, existence of a natural animal reservoir of C. cayetanensis could not be confirmed. Animals shedding oocysts in their faeces may be paratenic hosts. Investigators were able to successfully infect the following animals with C. cayetanensis: oysters, Asian freshwater clams (Corbicula fluminea), Swiss albino mice and guinea pigs. Future non-laboratory studies of animals should use PCR coupled with DNA sequencing to confirm that the species found is C. cayetanensis. The potential role of animals in the transport of oocysts and contamination of food, water, and soil could be explored through future primary research.

Evaluation of real-time qPCR-based methods to detect the DNA of the three protozoan parasites Cryptosporidium parvum, Giardia duodenalis and Toxoplasma gondii in the tissue and hemolymph of blue mussels (M. edulis)

The protozoan parasites Cryptosporidium spp., Giardia duodenalis and Toxoplasma gondii can be transmitted to humans through shellfish consumption. No standardized methods are available for their detection in these foods, and the performance of the applied methods are rarely described in occurrence studies. Through spiking experiments, we characterized different performance criteria (e.g. sensitivity, estimated limit of detection (eLD95_METH), parasite DNA recovery rates (DNA-RR)) of real-time qPCR based-methods for the detection of the three protozoa in mussel's tissues and hemolymph. Digestion of mussels tissues by trypsin instead of pepsin and the use of large buffer volumes was the most efficient for processing 50g-sample. Trypsin digestion followed by lipids removal and DNA extraction by thermal shocks and a BOOM-based technique performed poorly (e.g. eLD95_METH from 30 to >3000 parasites/g). But trypsin digestion and direct DNA extraction by bead-beating and FastPrep homogenizer achieved higher performance (e.g. eLD95_METH: 4-400 parasites/g, DNA-RR: 19-80%). Direct DNA recovery from concentrated hemolymph, by thermal shocks and cell lysis products removal was not efficient to sensitively detect the protozoa (e.g. eLD95_METH: 10-1000 parasites/ml, DNA-RR ≤ 24%). The bead-beating DNA extraction based method is a rapid and simple approach to sensitively detect the three protozoa in mussels using tissues, that can be standardized to different food matrices. However, quantification in mussels remains an issue.

Occurrence and distribution of fecal indicators and pathogenic bacteria in seawater and Perna perna mussel in the Gulf of Annaba (Southern Mediterranean)

The identification of fecal contamination in coastal marine ecosystems is one of the main requirements for evaluation of potential risks to human health. The objective of this study was to investigate the occurrence and distribution of fecal indicators and pathogenic bacteria in seawaters and mussels collected monthly during a period of 1 year from four different sites in Northeastern Algeria (sites S1 to S4), through biochemical and molecular analyses. Our research is the first to use molecular analysis to unambiguously identify the potentially pathogenic bacteria present in Algerian Perna perna mussels. The obtained results revealed that the levels of fecal indicator bacteria (FIB) from both P. perna and seawater samples largely exceeded the permissible limits at S2 and S3. This is mainly related to their location close to industrial and coastal activity zones, which contain a mixture of urban, agricultural, and industrial pollutants. Besides, P. perna collected from all sites were severalfold more contaminated by FIB than seawater samples, primarily during the warm season of the study period. Biochemical and molecular analyses showed that isolated bacteria from both seawater and mussels were mainly potentially pathogenic species such as E. coli, Salmonella spp., Staphylococcus spp., Klebsiella spp., Pseudomonas spp., and Proteus spp.

Epidemiology associated with the exposure to Toxoplasma gondii in Nunavik's Inuit population using the 2017 Qanuilirpitaa cross-sectional health survey

Foci of high seroprevalence against Toxoplasma gondii are observed in Nunavik, the Inuit land of Northern Quebec (Canada). Considering the rare occurrence of felids in the region, exposure is suspected to be driven by water- and food-borne transmission routes. Hypotheses were that drinking untreated water from natural sources and eating country food mostly raw increased the risk of exposure to the parasite. Data from 1,300 Inuit participants of the 2017 Nunavik Health Survey were included in three weighted robust Poisson regression models. The effect of three types of exposure variables: (1) water treatment (yes/no) and if country food was mostly eaten raw (yes/no); (2) main source of drinking water (bottled/municipal/natural) and frequency of country food consumption (continuous) and (3) drinking water risk (low/intermediate/high) and frequency of a raw country food consumption (continuous), on the presence of Toxoplasma antibodies were estimated. Models were adjusted for age, sex and ecological region, with multiple sensitivity analyses being performed. Toxoplasma gondii seroprevalences were consistently correlated with age quadratically, sex (prevalence ratio = PR_woman/man ranged from 1.18 to 1.22), ecological region (PR_{HudsonBay/HudsonStrait} ranged from 2.18 to 2.41; PR_{HudsonBay/UngavaBay} ranged from 1.52 to 1.59) and consuming bivalve mollusc/urchin (PR varied from 1.02 to 1.21) across all three models. Each increase of two consumptions per month of beluga (PR ranged from 1.01 to 1.03), seal liver (PR ranged from 1.01 to 1.02) and goose (PR ranged from 1.01 to 1.02) were also associated with seropositivity, albeit more clearly in models 2 and 3, while drinking water mainly from natural (PR of 1.47) or municipal (PR = 1.42) sources compared to bottled water, was correlated with seroprevalence, although results were compatible with the null. Our results suggest that both the oocyst- (mollusc/urchin, drinking water) and cyst-borne (walrus, seal liver and goose) transmission pathways could be present in Nunavik.

Blue mussel (Mytilus edulis)-A bioindicator of marine water contamination by protozoa: Laboratory and in situ approaches

AIMS

The protozoan parasites Cryptosporidium spp., Giardia duodenalis and Toxoplasma gondii are identified as public health priorities and are present in a wide variety of environments including the marine ecosystem. The objective of this study was to demonstrate that the marine bivalve blue mussel (Mytilus edulis) can be used as a tool to monitor the contamination of marine waters by the three protozoa over time.

METHODS AND RESULTS

In order to achieve a proof of concept, mussels were exposed to three concentrations of G. duodenalis cysts and Cryptosporidium parvum/T. gondii oocysts for 21 days, followed by 21 days of depuration in clear water. Then, natural contamination by these protozoa was sought for in wild marine blue mussels along the northwest coast of France to validate their relevance as bioindicators in the field. Our results highlighted that: (a) blue mussels bioaccumulated the parasites for 21 days, according to the conditions of exposure, and parasites could still be detected during the depuration period (until 21 days); (b) the percentage of protozoa-positive M. edulis varied under the degree of protozoan contamination in water; (c) mussel samples from eight out of nine in situ sites were positive for at least one of the protozoa.

CONCLUSIONS

The blue mussel M. edulis can bioaccumulate protozoan parasites over long time periods, according to the degree of contamination of waters they are inhabiting, and can highlight recent but also past contaminations (at least 21 days).

SIGNIFICANCE AND IMPACT OF THE STUDY

Mytilus edulis is a relevant bioaccumulators of protozoan (oo)cysts in laboratory and field conditions, hence its potential use for monitoring parasite contamination in marine waters.

Antibiotic-Resistant Bacteria in Clams-A Study on Mussels in the River Rhine

Bacterial infections have been treated effectively by antibiotics since the discovery of penicillin in 1928. A worldwide increase in the use of antibiotics led to the emergence of antibiotic resistant strains in almost all bacterial pathogens, which complicates the treatment of infectious diseases. Antibiotic-resistant bacteria play an important role in increasing the risk associated with the usage of surface waters (e.g., irrigation, recreation) and the spread of the resistance genes. Many studies show that important pathogenic antibiotic-resistant bacteria can enter the environment by the discharge of sewage treatment plants and combined sewage overflow events. Mussels have successfully been used as bio-indicators of heavy metals, chemicals and parasites; they may also be efficient bio-indicators for viruses and bacteria. In this study an influence of the discharge of a sewage treatment plant could be shown in regard to the presence of E. coli in higher concentrations in the mussels downstream the treatment plant. Antibiotic-resistant bacteria, resistant against one or two classes of antibiotics and relevance for human health could be detected in the mussels at different sampling sites of the river Rhine. No multidrug-resistant bacteria could be isolated from the mussels, although they were found in samples of the surrounding water body.

Prevalence, genotypes and risk factors for Toxoplasma gondii contamination in marine bivalve shellfish in offshore waters in eastern China

We conducted a large-scale epidemiological investigation to detect the prevalence of Toxoplasma gondii in four marine bivalve shellfish species collected from six representative coastal regions of Weihai, eastern China. Between January 2018 and December 2018, 14,535 marine bivalve shellfish pooled into 2907 samples were randomly collected and examined for T. gondii DNA by a nested PCR assay targeting B1 gene. The results showed that 2.8% (82) of the 2907 pooled samples were tested positive for T. gondii DNA. Two T. gondii genotype (ToxoDB Genotype #9 and ToxoDB Genotype #1) were identified PCR-restriction fragment length polymorphism analysis. Factors that were found significantly associated with the presence of T. gondii DNA in marine bivalve shellfish included the source of samples (being wild) (odds ratio [OR], 3.34; 95% confidence interval [CI], 2.00-5.84; p < 0.01), surface runoff near the sampling site (OR, 2.64; 95% CI, 1.47-4.72; p < 0.01), and presence of cats near the sampling site (OR, 1.77; 95% CI, 1.02-3.07; p = 0.04). Moreover, the prevalence of T. gondii DNA in marine bivalve shellfish correlated with temperature (Pearson's correlation: R = 0.75, p = 0.0049) and precipitation (R = 0.87, p = 0.00021). These findings provide new insights into the presence of T. gondii DNA in marine bivalve shellfish and highlight the impact of human activity on marine pollution by such an important terrestrial pathogen pollutant.

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.

Seroprevalence of Toxoplasma gondii among healthy blood donors in two locations in Tunisia and associated risk factors

Toxoplasma gondii is a protozoan parasite that can be transmitted to humans through a variety of routes including blood transfusion. This study aimed to investigate the seroprevalence of T. gondii infection and associated risk factors in healthy blood donors in Tunisia. A total of 800 healthy blood donors from two blood centers in south and coastal Tunisia were analyzed for anti-T. gondii IgG and IgM antibodies by indirect immunofluorescence assay (IFA) and enzyme-linked immunoassays (ELISA), respectively. Structured questionnaires were used to gather information on risk factors for T. gondii infection during collection. The overall seroprevalence was 44.4% of which 352 (44%) and 3 (0.4%) were positive for IgG and both IgG and IgM anti-T. gondii antibodies, respectively. Multivariate analysis showed that T. gondii seropositivity was significantly associated with the birth place (adjusted odds ratio [OR] = 2.72; 95% confidence interval [CI]: 1.49–4.94) and the age of the donors (adjusted OR = 4.98; 95% CI: 1.50–16.58) which are independent risk factors. In addition, the variables of hand washing before eating (adjusted OR = 0.52; 95% CI: 0.37–0.74) and living in an urban environment (adjusted OR = 0.30; 95% CI: 0.13–0.71) are two protective factors. This study provided the first data on the seroprevalence and epidemiology of T. gondii infection in healthy blood donors in Tunisia.

Parasitological Contamination of Vegetables Sold in Tunisian Retail Markets with Helminth Eggs and Protozoan Cysts

ABSTRACT

Foodborne diseases continue to represent an important threat to public health in many parts of the world and are particularly widespread in developing countries. They are essentially acquired through an oro-fecal route via the consumption of uncooked fruits and vegetables. This study evaluated the parasitological contamination of vegetables for sale to humans in Tunisian retail markets. A total of 240 samples of fresh vegetables were examined for helminth eggs and protozoan cysts and oocysts (collectively, (oo)cysts) contamination. The parasitic elements (helminth eggs and protozoan (oo)cysts) were concentrated by sucrose flotation and identified by microscopic examination. The molecular identification of Echinococcus granulosus eggs was carried out using PCR. Helminth eggs and protozoan (oo)cysts eggs were found in 12.5% of the unwashed vegetables, and the most common parasites observed in vegetables were coccidian oocysts (4.1%), Toxocara spp. (2.5%), hookworm (2.1%), and Taenia spp. (1.25%) eggs, followed by Pseudolimax butschlii (1.6%) and Entamoeba coli (1.6%) protozoan cysts. Furthermore, parasite contamination differed significantly from one city to another. Taeniid eggs were identified by PCR as E. granulosus sensu stricto (s.s.) (genotype G1). To our knowledge, this study highlights for the first time in Tunisia that fresh vegetables for sale in markets are contaminated with helminths and protozoan cysts, which are potentially pathogenic for humans. The control of these pathogens is in part a question of sanitary education, especially for retail vendors, and in part of improvement in hygiene measures throughout the food production chain, from the field to the consumer.

HIGHLIGHTS

Comparative evaluation of loop-mediated isothermal amplification (LAMP) vs qPCR for detection of Toxoplasma gondii oocysts DNA in mussels

The apicomplexan parasite Toxoplasma gondii can infect humans and cause toxoplasmosis. T. gondii has been highly prioritized among the foodborne parasites regarding its global impact on public health. Human infection can occur through multiple routes, including the ingestion of raw or undercooked food contaminated with T. gondii oocysts, such as fresh produce and bivalves. As filter-feeders, bivalves can accumulate and concentrate contaminants, including protozoan (oo)cysts. Although detection of T. gondii in different bivalves by molecular techniques (PCR and qPCR) has been achieved, routine application is currently limited by lack of sensitivity or equipment costs. Here, we describe the assessment of a loop-mediated isothermal amplification (LAMP)-based assay to detect T. gondii oocysts in spiked mussels. Detection limit was down to 5 oocysts/g in tissue and 5 oocyst/ml in hemolymph, and, under the experimental conditions tested, LAMP was found to provide a promising alternative to qPCR.

Efficiency of the Q3 lab-on-chip Real Time-PCR platform for detecting protozoan pathogens in bivalve mollusks

The zoonotic protozoan parasites Toxoplasma gondii, Cryptosporidium parvum and Giardia duodenalis have been recorded worldwide in economically important edible shellfish, and are thus likely to represent a significant public health risk. Therefore, an innovative, user-friendly diagnostic tool is required in order to improve food safety control. The Q3 system is a miniaturized platform whose efficiency and applicability were investigated and compared with results obtained using standard Real-Time PCR. Tanks of saltwater containing acclimated Mytilus galloprovincialis, Ruditapes philippinarum and Ostrea edulis specimens were spiked with purified Cryptosporidium, Giardia and Toxoplasma cysts/oocysts at different concentrations (i.e., 10³, 10⁴ and 10⁵). We then collected 30 specimens for each shellfish species from each group at 24 h and 72 h post-contamination. After DNA extraction, we tested all samples by Real-Time-PCR and Q3, and evaluated the sensitivity, specificity, predictive values, repeatability and concordance between the two systems. Concordance between Real-Time-PCR and Q3 was very good (p < 0.01), especially for Toxoplasma in M. galloprovincialis at both 24 h and 72 h after contamination, and in O. edulis at 72 h. The ability of Q3 to detect all the investigated pathogens was similar to that of Real-Time-PCR, and Q3 was efficient in detecting Toxoplasma in both M. galloprovincialis and O. edulis. This is the first study concerning the use of lab-on-chip technology in a food matrix, and in edible marine mollusks in particular.

Cyclospora cayetanensis infection in humans: biological characteristics, clinical features, epidemiology, detection method and treatment

Cyclospora cayetanensis, a coccidian parasite that causes protracted and relapsing gastroenteritis, has a short recorded history. At least 54 countries have documented C. cayetanensis infections and 13 of them have recorded cyclosporiasis outbreaks. Cyclospora cayetanensis infections are commonly reported in developing countries with low-socioeconomic levels or in endemic areas, although large outbreaks have also been documented in developed countries. The overall C. cayetanensis prevalence in humans worldwide is 3.55%. Among susceptible populations, the highest prevalence has been documented in immunocompetent individuals with diarrhea. Infections are markedly seasonal, occurring in the rainy season or summer. Cyclospora cayetanensis or Cyclospora-like organisms have also been detected in food, water, soil and some other animals. Detection methods based on oocyst morphology, staining and molecular testing have been developed. Treatment with trimethoprim-sulfamethoxazole (TMP-SMX) effectively cures C. cayetanensis infection, whereas ciprofloxacin is less effective than TMP-SMX, but is suitable for patients who cannot tolerate co-trimoxazole. Here, we review the biological characteristics, clinical features, epidemiology, detection methods and treatment of C. cayetanensis in humans, and assess some risk factors for infection with this pathogen.

Cyclospora cayetanensis and Cyclosporiasis: An Update

Cyclospora cayetanensis is a coccidian parasite of humans, with a direct fecal-oral transmission cycle. It is globally distributed and an important cause of foodborne outbreaks of enteric disease in many developed countries, mostly associated with the consumption of contaminated fresh produce. Because oocysts are excreted unsporulated and need to sporulate in the environment, direct person-to-person transmission is unlikely. Infection by C. cayetanensis is remarkably seasonal worldwide, although it varies by geographical regions. Most susceptible populations are children, foreigners, and immunocompromised patients in endemic countries, while in industrialized countries, C. cayetanensis affects people of any age. The risk of infection in developed countries is associated with travel to endemic areas and the domestic consumption of contaminated food, mainly fresh produce imported from endemic regions. Water and soil contaminated with fecal matter may act as a vehicle of transmission for C. cayetanensis infection. The disease is self-limiting in most immunocompetent patients, but it may present as a severe, protracted or chronic diarrhea in some cases, and may colonize extra-intestinal organs in immunocompromised patients. Trimetoprim-sulfamethoxazole is the antibiotic of choice for the treatment of cyclosporiasis, but relapses may occur. Further research is needed to understand many unknown epidemiological aspects of this parasitic disease. Here, we summarize the biology, epidemiology, outbreaks, clinical symptoms, diagnosis, treatment, control and prevention of C. cayetanensis; additionally, we outline future research needs for this parasite.

Comparison of PCR assays to detect Toxoplasma gondii oocysts in green-lipped mussels (Perna canaliculus)

Toxoplasma gondii is recognised as an important pathogen in the marine environment, with oocysts carried to coastal waters in overland runoff. Currently, there are no standardised methods to detect T. gondii directly in seawater to assess the extent of marine ecosystem contamination, but filter-feeding shellfish may serve as biosentinels. A variety of PCR-based methods have been used to confirm presence of T. gondii DNA in marine shellfish; however, systematic investigations comparing molecular methods are scarce. The primary objective of this study was to evaluate analytical sensitivity and specificity of two nested-PCR (nPCR) assays targeting dhps and B1 genes and two real-time (qPCR) assays targeting the B1 gene and a 529-bp repetitive element (rep529), for detection of T. gondii. These assays were subsequently validated for T. gondii detection in green-lipped mussel (Perna canaliculus) haemolymph using oocyst spiking experiments. All assays could reliably detect 50 oocysts spiked into mussel haemolymph. The lowest limit of detection was 5 oocysts using qPCR assays, with the rep529 primers performing best, with good correlation between oocyst concentrations and Cq values, and acceptable efficiency. Assay specificity was evaluated by testing DNA from closely related protozoans, Hammondia hammondi, Neospora caninum, and Sarcocystis spp. Both nPCR assays were specific to T. gondii. Both qPCR assays cross-reacted with Sarcocystis spp. DNA, and the rep529 primers also cross-reacted with N. caninum DNA. These studies suggest that the rep529 qPCR assay may be preferable for future mussel studies, but direct sequencing is required for definitive confirmation of T. gondii DNA detection.

Environmental transmission of Toxoplasma gondii: Oocysts in water, soil and food

Toxoplasma gondii is a zoonotic protozoan parasite that can cause morbidity and mortality in humans, domestic animals, and terrestrial and aquatic wildlife. The environmentally robust oocyst stage of T. gondii is fundamentally critical to the parasite's success, both in terms of its worldwide distribution as well as the extensive range of infected intermediate hosts. Despite the limited definitive host species (domestic and wild felids), infections have been reported on every continent, and in terrestrial as well as aquatic environments. The remarkable resistance of the oocyst wall enables dissemination of T. gondii through watersheds and ecosystems, and long-term persistence in diverse foods such as shellfish and fresh produce. Here, we review the key attributes of oocyst biophysical properties that confer their ability to disseminate and survive in the environment, as well as the epidemiological dynamics of oocyst sources including domestic and wild felids. This manuscript further provides a comprehensive review of the pathways by which T. gondii oocysts can infect animals and people through the environment, including in contaminated foods, water or soil. We conclude by identifying critical control points for reducing risk of exposure to oocysts as well as opportunities for future synergies and new directions for research aimed at reducing the burden of oocyst-borne toxoplasmosis in humans, domestic animals, and wildlife.

Comparison of Cryptosporidium oocyst recovery methods for their applicability for monitoring of consumer-ready fresh shellfish

Growing demand for fresh, unprocessed food favours the emergence of Cryptosporidium infections in humans. Mainly it is food of plant origin or unpasteurized milk which have been involved in food-borne outbreaks of cryptosporidiosis. So far consumption of shellfish contaminated with Cryptosporidium were not associated with human infections although such as possibility exists. In this study an attempt was undertaken to evaluate the analytical performance of three commonly used methods for recovery of Cryptosporidium oocysts from shellfish: i) pepsin digestion of shellfish in conjunction with immunomagnetic separation (IMS) of oocysts (method A), ii) pepsin-HCl treatment of shellfish homogenate without IMS (method B), and iii) a strainer method with direct oocyst extraction and separation from shellfish tissue using IMS (method C). Each method's performance was assessed according to the ISO standard requirements by testing shellfish homogenates seeded with different numbers of C. parvum oocysts. Two groups of parameters were compared, encompassing precision (coefficient of variation (CV)) and accuracy of measurements. These were described by linear regression models allowing calculation of the methods' limits of detection (LOD) and quantification (LOQ). In addition, oocyst recovery efficiencies from shellfish were calculated for each method. All three compared methods allowed for at least 66% recovery of Cryptosporidium oocysts from the tested samples. The best recovery (83.3-100%) in the whole range of tested suspensions was obtained for method C. The accuracy of method B was better (linearity of r² = 0.9996 in the full measurement range) than that of method A (r² = 0.968). Method C showed the best accuracy (r² = 1) and precision (CV 0.2-14.1). Compared to other methods it was also characterised by the best LOD and LOQ, attaining ≅4 and ≅12 oocysts per 3 g of tested shellfish sample respectively. Despite a lack of the ability of method A to give the proportional results in oocysts recovery (non-linearity of the method) compared to the reference values, it achieved the highest LOD and LOQ values among the tested methods. As demonstrated here, the most efficient method for extraction of Cryptosporidium oocysts from shellfish tissues was method C employing sample homogenisation and separation of oocysts from tissue debris using IMS. Used alone this method does not in fact allow for identification of Cryptosporidium species but delivers quantitative results concerning the level of food contamination by parasites.

Protocol standardization for the detection of Giardia cysts and Cryptosporidium oocysts in Mediterranean mussels (Mytilus galloprovincialis)

Marine bivalve shellfish are of public health interest because they can accumulate pollutants in their tissues. As they are usually consumed raw or lightly cooked, they are considered to be a possible source of foodborne infections, including giardiosis and cryptosporidiosis. Although data indicating contamination of shellfish with Giardia cysts and Cryptosporidium oocysts have been published, comparing results from different studies is difficult, as there is no standardized protocol for the detection and quantification of these parasites in mussels, and different researchers have used different analytical approaches. The aim of this study was to identify and characterize the most sensitive protocol for the detection of Giardia cysts and Cryptosporidium oocysts in shellfish. In an effort to test the sensitivity and the detection limits of the protocol, every step of the process was investigated, from initial preparation of the mussel matrix through detection of the parasites. Comparative studies were conducted, including several methods previously applied by other researchers, on commercial mussels Mytilus galloprovincialis spiked with a known number of (oo)cysts of both parasites. As preparation of the mussel matrix plays an important role in the sensitivity of the method, different techniques were tested. These included: (ia) removal of the coarse particles from the matrix with sieving, (ib) extraction of the lipids with diethyl ether, and (ic) artificial digestion of the matrix with pepsin digestion solution, and (ii) the use or not of immunomagnetic separation (IMS) for the concentration of the (oo)cysts. Pre-treatment of the mussel homogenate with pepsin digestion solution, followed by IMS, then detection with a direct immunofluorescence assay, achieved the highest sensitivity: 32.1% (SD: 21.1) of Giardia cysts and 61.4% (SD: 26.2) Cryptosporidium oocysts were recovered, with a detection limit of 10 (oo)cysts per g of mussel homogenate. The outcome of the current study was the standardization of a protocol, with defined detection limits, for the detection of these two protozoan transmission stages in mussels, in order to be used as a reference technique in future studies. Further advantages of this protocol are that it uses the whole mussel as a starting material and does not require difficult handling procedures. The method has potential to be applied in larger surveys and, potentially, to other species of shellfish for the detection of these parasites. However, the composition (lipid to protein ratio) may be of relevance for detection efficiency for some other species of shellfish.

Toxoplasma gondii and Other Zoonotic Protozoans in Mediterranean Mussel ( Mytilus galloprovincialis) and Blue Mussel ( Mytilus edulis): A Food Safety Concern?

Mediterranean mussels ( Mytilus galloprovincialis) and blue mussels ( Mytilus edulis) are among the most consumed fishery products, but they are frequent vehicles of foodborne infection worldwide. In this study, we investigated the occurrence and seasonality of zoonotic protozoans in mussels farmed or sold at retail outlets in Italy. We collected and tested 1,440 M. galloprovincialis and 180 M. edulis. Pooled samples were molecularly tested for Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii and then sequenced. Sixty-two (45.9%; 95% confidence interval, 37.5 to 54.3%) mussel pools tested positive for one or more of the investigated pathogens. Both Mytilus species and samples from all the investigated areas harbored pathogens. Mussels were statistically more contaminated by Cryptosporidium spp., followed by T. gondii and G. duodenalis assemblage A, and M. galloprovincialis was more contaminated than M. edulis ( P < 0.01). Contamination was more likely in mussels at retail outlets ( P < 0.05) than in those from farms and in mussels collected in spring ( P < 0.01) than in other seasons. This is the first report of T. gondii found in M. galloprovincialis in Italy and in M. edulis in Europe. The detection of zoonotic protozoans in a widely consumed food source indicates the need for a more detailed microbiological risk analysis, especially considering that bivalve mollusks are often consumed raw worldwide.

Public health risks associated with food-borne parasites

Parasites are important food‐borne pathogens. Their complex lifecycles, varied transmission routes, and prolonged periods between infection and symptoms mean that the public health burden and relative importance of different transmission routes are often difficult to assess. Furthermore, there are challenges in detection and diagnostics, and variations in reporting. A Europe‐focused ranking exercise, using multicriteria decision analysis, identified potentially food‐borne parasites of importance, and that are currently not routinely controlled in food. These are Cryptosporidium spp., Toxoplasma gondii and Echinococcus spp. Infection with these parasites in humans and animals, or their occurrence in food, is not notifiable in all Member States. This Opinion reviews current methods for detection, identification and tracing of these parasites in relevant foods, reviews literature on food‐borne pathways, examines information on their occurrence and persistence in foods, and investigates possible control measures along the food chain. The differences between these three parasites are substantial, but for all there is a paucity of well‐established, standardised, validated methods that can be applied across the range of relevant foods. Furthermore, the prolonged period between infection and clinical symptoms (from several days for Cryptosporidium to years for Echinococcus spp.) means that source attribution studies are very difficult. Nevertheless, our knowledge of the domestic animal lifecycle (involving dogs and livestock) for Echinoccocus granulosus means that this parasite is controllable. For Echinococcus multilocularis, for which the lifecycle involves wildlife (foxes and rodents), control would be expensive and complicated, but could be achieved in targeted areas with sufficient commitment and resources. Quantitative risk assessments have been described for Toxoplasma in meat. However, for T. gondii and Cryptosporidium as faecal contaminants, development of validated detection methods, including survival/infectivity assays and consensus molecular typing protocols, are required for the development of quantitative risk assessments and efficient control measures.

Seroprevalence Survey for Microsporidia in Common Bottlenose Dolphin ( Tursiops truncatus): Example of a Quantitative Approach Based on Immunoblotting

Little is known about microsporidiosis pathogenicity in cetaceans. Here we report seroprevalence of 76% for microsporidia in blood samples from common bottlenose dolphins ( Tursiops truncatus), from animals managed under human care ( n=108) or captured for health assessments ( n=13) and released.