Cryptosporidium and Giardia in commercial and non-commercial oysters (Crassostrea gigas) and water from the Oosterschelde, the Netherlands

Occurrence of Cryptosporidium oocysts in commercial oysters in southern Thailand

The enteric parasite Cryptosporidium is spread through the fecal-oral pathway, most commonly by the consumption of contaminated water but also through food. Because eating raw or barely cooked shellfish might put consumers at risk for cryptosporidiosis, identifying the parasite in oysters is important for public health. A total of 240 oysters, collected from two shellfish aquaculture sites in Thailand's Gulf coast, Nakhon Si Thammarat and Surat Thani, were tested for the presence of Cryptosporidium. Escherichia coli, enterococci, and thermotolerant coliform total levels were measured to assess seawater quality in the shellfish production regions. Oocysts of Cryptosporidium spp. were detected in 13.8% of the samples processed by immunofluorescence analyses. The detection of Cryptosporidium spp. oocysts in oysters obtained from Surat Thani (17.5%) was higher than in those obtained from Nakhon Si Thammarat (9.2%). The difference in detection of positive samples obtained from Nakhon Si Thammarat and those obtained from Surat Thani may be attributed to the effects of physical, ecological, and anthropogenic conditions, resulting in an increased level of marine water contamination by Cryptosporidium spp. oocysts. These findings demonstrate that native commercial oysters obtained from Thailand's southern Gulf coast contained Cryptosporidium spp. oocysts which might serve as a source of human infection. Consequently, these findings pose a serious public health concern and suggest that more quality control measures need to be implemented by the oyster aquaculture business to ensure the safety of seafood.

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.

Prevalence, distribution and environmental effects on faecal indicator bacteria and pathogens of concern in commercial shellfish production areas in a subtropical region of a developing country (Santa Catarina, Brazil)

This paper reviews recent literature on the abundance and distribution of faecal indicator bacteria and pathogens in shellfish production areas in the state of Santa Catarina, on the subtropical coast of Brazil. This state supplies > 95% of the national production of shellfish. Microbiological monitoring data were mapped using GIS and the results compared with those from other countries. Coastal human population is the main predictive parameter for faecal bacteria in the production areas. Temporal variations of the bacteria can also be predicted by solar radiation and rainfall. The prevalence of pathogens such as hepatitis A virus, human norovirus, Salmonella spp. and Vibrio spp. does not differ substantially from that in developed countries. The information reported here can be used to inform development of microbiological risk profiles for shellfish production areas.

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.

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.

Investigations from Northern Greece on mussels cultivated in areas proximal to wastewaters discharges, as a potential source for human infection with Giardia and Cryptosporidium

Marine bivalves are usually cultivated in shallow, estuarine waters where there is a high concentration of nutrients. Many micro-pollutants, including the protozoan parasites Giardia duodenalis and Cryptosporidium spp., which also occur in such environments, may be concentrated in shellfish tissues during their feeding process. Shellfish can thus be considered as vehicles for foodborne infections, as they are usually consumed lightly cooked or raw. Therefore, the main objective of this study was to investigate the presence of both parasites in Mediterranean mussels, Mytilus galloprovincialis that are cultivated in Thermaikos Gulf, North Greece, which is fed by four rivers that are contaminated with both protozoa. Moreover, the occurrence of these protozoa was monitored in treated wastewaters from 3 treatment plants that discharge into the gulf. In order to identify potential sources of contamination and to estimate the risk for human infection, an attempt was made to genotype Giardia and Cryptosporidium in positive samples. Immunofluorescence was used for detection and molecular techniques were used for both detection and genotyping of the parasites. In total, 120 mussel samples, coming from 10 farms, were examined for the presence of both protozoa over the 6-month farming period. None of them were found positive by immunofluorescence microscopy for the presence of parasites. Only in 3 mussel samples, PCR targeting the GP60 gene detected Cryptosporidium spp. DNA, but sequencing was not successful. Thirteen out of 18 monthly samples collected from the 3 wastewater treatment plants, revealed the presence of Giardia duodenalis cysts belonging to sub-assemblage AII, at relatively low counts (up to 11.2 cysts/L). Cryptosporidium oocysts (up to 0.9 oocysts/L) were also detected in 4 out of 8 samples, although sequencing was not successful at any of the target genes. At the studied location and under the sampling conditions described, mussels tested were not found to be harboring Giardia cysts and the presence of Cryptosporidium was found only in few cases (by PCR detection only). Our results suggest that the likelihood that mussels from these locations act as vehicles of human infection for Giardia and Cryptosporidium seems low.

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.

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.

Giardia: an under-reported foodborne parasite

Foodborne zoonotic pathogens are a serious public health issue and result in significant global economic losses. Despite their importance to public health, epidemiological data on foodborne diseases including giardiasis caused by the enteric parasite, Giardia duodenalis, are lacking. This parasite is estimated to cause ∼28.2 million cases of diarrhoea each year due to contamination of food, but very few foodborne outbreaks have been documented due to the limitations of current detection as well as surveillance methods. The current method for the recovery of Giardia cysts from food matrices using immunomagnetic separation requires further standardisation and cost reduction before it can be widely used. It also should incorporate downstream molecular procedures for genotyping, and traceback and viability analyses. Foodborne giardiasis can be potentially controlled through improvements in national disease surveillance systems and the establishment of Hazard Analysis and Critical Control Point interventions across the food chain. Studies are needed to assess the true prevalence and public health impact of foodborne giardiasis.

Assessing viability and infectivity of foodborne and waterborne stages (cysts/oocysts) of Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii: a review of methods

Giardia duodenalis, Cryptosporidium spp. and Toxoplasma gondii are protozoan parasites that have been highlighted as emerging foodborne pathogens by the Food and Agriculture Organization of the United Nations and the World Health Organization. According to the European Food Safety Authority, 4786 foodborne and waterborne outbreaks were reported in Europe in 2016, of which 0.4% were attributed to parasites including Cryptosporidium, Giardia and Trichinella. Until 2016, no standardized methods were available to detect Giardia, Cryptosporidium and Toxoplasma (oo)cysts in food. Therefore, no regulation exists regarding these biohazards. Nevertheless, considering their low infective dose, ingestion of foodstuffs contaminated by low quantities of these three parasites can lead to human infection. To evaluate the risk of protozoan parasites in food, efforts must be made towards exposure assessment to estimate the contamination along the food chain, from raw products to consumers. This requires determining: (i) the occurrence of infective protozoan (oo)cysts in foods, and (ii) the efficacy of control measures to eliminate this contamination. In order to conduct such assessments, methods for identification of viable (i.e. live) and infective parasites are required. This review describes the methods currently available to evaluate infectivity and viability of G. duodenalis cysts, Cryptosporidium spp. and T. gondii oocysts, and their potential for application in exposure assessment to determine the presence of the infective protozoa and/or to characterize the efficacy of control measures. Advantages and limits of each method are highlighted and an analytical strategy is proposed to assess exposure to these protozoa.

Cryptosporidium spp. Contamination in Perna perna Mussels Destined for Human Consumption in Southeastern Rio de Janeiro, Brazil

Cryptosporidium spp. has been recognized as an important pathogen. As bivalve mollusks are noted as potential sources of several pathogens due to their consumption as foodstuffs, the aim of this study was to investigate the occurrence of Cryptosporidium spp. oocysts in Perna perna mussels and in seawater samples from a mussel farm in Southeastern Brazil, where mussels are grown directly in the sea, attached to ropes. Oocysts were observed by microscopy and confirmed by an enzyme-linked immunosorbent assay. Oocysts were present in mussel gills and GI tracts, as well as in the seawater. Of the 100 females, 10% and 11% showed contaminated GI tracts and gills, respectively, while this rate was lower in males, at 5% and 8.9%. Oocysts were present in higher amounts in the GI tract compared to gills and water. Contamination of the study area is apparent, leading to public health risks. More in-depth studies are needed, including molecular investigations, to identify Cryptosporidium species in mussels, as well as the implementation of monitoring actions in animals destined for human consumption.

An overview of methods/techniques for the detection of Cryptosporidium in food samples

Cryptosporidium is one of the most important parasitic protozoa of concern within the food production industry, worldwide. This review describes the evolution and its development, and it monitors the methodology that has been used for Cryptosporidium in food material since 1984, when the first publication appeared regarding the detection of Cryptosporidium parvum in food materials. The methods that are currently being used for the detection of Cryptosporidium oocysts in food material (mainly vegetables) and all of the other available published methods are discussed in this review. Generating more consistent and reliable data should lead to a better understanding of the occurrence, transport and fate of the oocysts in food material. Improvements in monitoring and developing effective methodology, along with food security, offer more practical possibilities for both the developed and developing worlds.

Mussels (Perna perna) as bioindicator of environmental contamination by Cryptosporidium species with zoonotic potential

Sources of contamination such as animal feces runoff, organic fertilizer application, and the release of partially treated or untreated sewage can lead to the contamination of aquatic environments by Cryptosporidium spp. The quality of mussels as food is closely related to the sanitary conditions of the marine environment where these bivalves are found. Marine mollusks are filter feeders that are able to retain Cryptosporidium oocysts in their tissue, thus functioning as bioindicators. A total of 72 pooled mussel samples of the species Perna perna were collected at two sites (A and B) in the municipality of Mangaratiba, Rio de Janeiro State, Brazil. Sampling involved removal of 30 mussels, from each collection site every month for one year. The 30 mussels from each sampling were then allocated into three groups of 10. Two Cryptosporidium spp. genes (18S and GP60) were targeted for DNA amplification from the samples obtained. After purification, all of the products obtained were sequenced and phylogenetic analyses were performed. Of the 72 samples analyzed using the nested-PCR for the 18S gene target, 29.2% were positive for the presence of Cryptosporidium spp. Of these samples, 52.4% were collected at site A (ie 11/21) and 47.6% at site B (ie 10/21). The 18S genes of all the samples considered positive for Cryptosporidium spp. were sequenced, and the following three species were identified: Cryptosporidium parvum, C. meleagridis, and C. andersoni. Three distinct C. parvum subtypes (IIaA19G2R2; IIaA20G2R2; IIaA20G3R2) were identified using the GP60 gene. More studies to evaluate the zoonotic potential of this species should be performed as both sampling locations contain human and/or animal fecal contaminants.

•

Different species of Cryptosporidium diagnosed in Perna perna mussels.

•

C. parvum subtypes of IIa zoonotic subfamily diagnosed in P. perna mussels.

•

First report of the zoonotic species C. meleagridis in Brazilian mollusk bivalves.

•

Mollusks bivalves used as bioindicator of environmental pollution.

Detection of Cryptosporidium parvum in environmental soil and vegetables

Cryptosporidium parvum is a zoonotic protozoan parasite that causes cryptosporidial enteritis. Numerous outbreaks of cryptosporidiosis have been reported worldwide. Cryptosporidium is transmitted to hosts via consumption of contaminated water and food but also by direct contact with contaminated soil or infected hosts. The present study investigated farm soil collected from 34 locations along the western Korean peninsula and 24 vegetables purchased from local grocery markets in Seoul. The soil and vegetable samples were examined by real-time polymerase chain reaction (qPCR) to estimate the risk of infection. Eleven of 34 locations (32.4%) and 3 of 24 vegetable samples (12.5%) were contaminated with Cryptosporidium parvum, as confirmed by TaqI enzyme digestion of qPCR products and DNA sequencing. It is suggested that Cryptosporidium infection can be mediated via farm soil and vegetables. Therefore, it is necessary to reduce contamination of this organism in view of public health.

Tools and methods for detecting and characterizing giardia, cryptosporidium, and toxoplasma parasites in marine mollusks

Foodborne infections are of public health importance and deeply impact the global economy. Consumption of bivalve mollusks generates risk for humans because these filtering aquatic invertebrates often concentrate microbial pathogens from their environment. Among them, Giardia, Cryptosporidium, and Toxoplasma are major parasites of humans and animals that may retain their infectivity in raw or undercooked mollusks. This review aims to detail current and future tools and methods for ascertaining the load and potential infectivity of these parasites in marine bivalve mollusks, including sampling strategies, parasite extraction procedures, and their characterization by using microscopy and/or molecular techniques. Method standardization should lead to better risk assessment of mollusks as a source of these major environmental parasitic pathogens and to the development of safety regulations, similar to those existing for bacterial and viral pathogens encountered in the same mollusk species.

Determination of the recovery efficiency of cryptosporidium oocysts and giardia cysts from seeded bivalve mollusks

The intestinal parasites Cryptosporidium and Giardia are transmitted by water and food and cause human gastroenteritis. Filter-feeding bivalve mollusks, such as oysters and mussels, filter large volumes of water and thus concentrate such pathogens, which makes these bivalves potential vectors of disease. To assess the risk of infection from consumption of contaminated bivalves, parasite numbers and parasite recovery data are required. A modified immunomagnetic separation (IMS) procedure was used to determine Cryptosporidium oocyst and Giardia cyst numbers in individually homogenized oysters (Crassostrea gigas) and mussels (Mytilus edulis). About 12% of the commercial bivalves were positive, with low (oo)cyst numbers per specimen. The recovery efficiency of the IMS procedure was systematically evaluated. Experiments included seeding of homogenized bivalves and whole animals with 100 to 1,000 (oo)cysts. Both seeding procedures yielded highly variable recovery rates. Median Cryptosporidium recoveries were 7.9 to 21% in oysters and 62% in mussels. Median Giardia recoveries were 10 to 25% in oysters and 110% in mussels. Giardia recovery was significantly higher than Cryptosporidium recovery. (Oo)cysts were less efficiently recovered from seeded whole animals than from seeded homogenates, with median Cryptosporidium recoveries of 5.3% in oysters and 45% in mussels and median Giardia recoveries of 4.0% in oysters and 82% in mussels. Both bivalve homogenate seeding and whole animal seeding yielded higher (oo)cyst recovery in mussels than in oysters, likely because of the presence of less shellfish tissue in IMS when analyzing the smaller mussels compared with the larger oysters, resulting in more efficient (oo)cyst extraction. The data generated in this study may be used in the quantitative assessment of the risk of infection with Cryptosporidium or Giardia associated with the consumption of raw bivalve mollusks. This information may be used for making risk management decisions.

Depletion of Cryptosporidium parvum oocysts from contaminated sewage by using freshwater benthic pearl clams (Hyriopsis schlegeli)

The freshwater benthic pearl clam, Hyriopsis schlegeli, was experimentally exposed to Cryptosporidium parvum oocysts, and it was verified that the oocysts were eliminated predominantly via the fecal route, retaining their ability to infect cultured cells (HCT-8). The total fecal oocyst elimination rate was more than 90% within 5 days after exposure to the oocysts. H. schlegeli was able to survive in the final settling pond of a sewage plant for long periods, as confirmed by its pearl production. In the light of these findings, the clam was placed in the final settling pond in a trial to test its long-term efficacy in depleting oocysts contaminating the pond water. The number of clams placed was set to ensure a theoretical oocyst removal rate of around 50%, and the turbidity and the density of feed microbes in the overflow trough water of the pond were about 35% and 40 to 60% lower, respectively, than in the control water throughout the year. It was found that the clam feces containing oocysts were sufficiently heavy for them to settle to the bottom of the pond, despite the upward water flow. From these results, we concluded that efficient depletion of oocysts in the sewage water of small or midscale sewage treatment plants can be achieved by appropriate placement of H. schlegeli clams.

Investigation of Toxoplasma gondii presence in farmed shellfish by nested-PCR and real-time PCR fluorescent amplicon generation assay (FLAG)

To evaluate the presence of Toxoplasma gondii in edible farmed shellfish, 1734 shellfish specimens i.e., 109 Crassostrea gigas (6 pools), 660 Mytilus galloprovincialis (22 pools), 804 Tapes decussatus (28 pools) and 161 Tapes philippinarum (6 pools), were collected from the Varano Lagoon (Apulia, Italy). Shellfish from 62 pools were subjected to two molecular techniques: a nested-PCR assay, and a fluorescent amplicon generation (FLAG) real-time PCR assay, both based on the multi-copy B1 target, were performed. One pooled sample of gills from C. gigas and one pooled sample of haemolymphs from T. decussatus were assessed as positive for T. gondii DNA by both techniques. The results demonstrated the presence of T. gondii in edible farmed C. gigas and T. decussatus and indicate that there may be a considerable health threat involved in eating contaminated raw shellfish.

Pathogenic Vibrio species in dutch shellfish destined for direct human consumption

Vibrio parahaemolyticus is a common cause of shellfish-related gastroenteritis all over the world. V. parahaemolyticus and Vibrio alginolyticus have previously been detected in water samples from the Oosterschelde, a large inlet on the North Sea, which is used for both recreational purposes and shellfish production. In 2006, oysters (Crassostrea gigas) from a noncommercial oyster bed in the Oosterschelde and oysters bought in Dutch fish shops were tested for the presence of pathogenic Vibrio species; in 2007 and 2008, oysters (C. gigas) and mussels (Mytilus edulis) from Oosterschelde production areas were examined. Total Vibrio numbers were related to water temperatures to study joint patterns. Vibrio was found in oysters and mussels from the production areas, and levels ranged from 6 to 622 most probable number (MPN) per g in oysters and 6 to 62 MPN/g in mussels. Vibrio levels in oysters from fish shops were 231 to >333 MPN/g, whereas levels in noncommercial oysters ranged from 231 to >2,398 MPN/g. About 80% of the isolated strains were V. alginolyticus, and approximately 10% were identified as V. parahaemolyticus. Vibrio counts in shellfish samples increased with increasing water temperature and declined when water temperatures dropped; Vibrio was not detected when water temperatures declined to <13.5 degrees C. Based on the obtained results and the known high V. parahaemolyticus dose (>10(4) cells per serving of oysters) required for infection, it is concluded that the risk of gastrointestinal infections with V. parahaemolyticus through consumption of shellfish from the Oosterschelde production sites is presumably low.

Cryptosporidium: detection in water and food

Water and food are major environmental transmission routes for Cryptosporidium, but our ability to identify the spectrum of oocyst contributions in current performance-based methods is limited. Determining risks in water and foodstuffs, and the importance of zoonotic transmission, requires the use of molecular methods, which add value to performance-based morphologic methods. Multi-locus approaches increase the accuracy of identification, as many signatures detected in water originate from species/genotypes that are not infectious to humans. Method optimisation is necessary for detecting small numbers of oocysts in environmental samples consistently, and further work is required to (i) optimise IMS recovery efficiency, (ii) quality assure performance-based methods, (iii) maximise DNA extraction and purification, (iv) adopt standardised and validated loci and primers, (v) determine the species and subspecies range in samples containing mixtures, and standardising storage and transport matrices for validating genetic loci, primer sets and DNA sequences.

Emerging food-borne parasites

Parasitic food-borne diseases are generally underrecognised, however they are becoming more common. Globalization of the food supply, increased international travel, increase of the population of highly susceptible persons, change in culinary habits, but also improved diagnostic tools and communication are some factors associated with the increased diagnosis of food-borne parasitic diseases worldwide. This paper reviews the most important emerging food-borne parasites, with emphasis on transmission routes. In a first part, waterborne parasites transmitted by contaminated food such as Cyclospora cayetanensis, Cryptosporidium and Giardia are discussed. Also human fasciolosis, of which the importance has only been recognised in the last decades, with total numbers of reported cases increasing from less than 3000 to 17 million, is looked at. Furthermore, fasciolopsiosis, an intestinal trematode of humans and pigs belongs to the waterborne parasites as well. A few parasites that may be transmitted through faecal contamination of foods and that have received renewed attention, such as Toxoplasma gondii, or that are (re-)emerging, such as Trypanosoma cruzi and Echinococcus spp., are briefly reviewed. In a second part, meat-borne parasite infections are reviewed. Humans get infected by eating raw or undercooked meat infected with cyst stages of these parasites. Meat inspection is the principal method applied in the control of Taenia spp. and Trichinella spp. However, it is often not very sensitive, frequently not practised, and not done for T. gondii and Sarcocystis spp. Meat of reptiles, amphibians and fish can be infected with a variety of parasites, including trematodes (Opisthorchis spp., Clonorchis sinensis, minute intestinal flukes), cestodes (Diphyllobothrium spp., Spirometra), nematodes (Gnathostoma, spp., anisakine parasites), and pentastomids that can cause zoonotic infections in humans when consumed raw or not properly cooked. Another important zoonotic food-borne trematode is the lungfluke (Paragonimus spp.). Traditionally, these parasitic zoonoses are most common in Asia because of the particular food practices and the importance of aquaculture. However, some of these parasites may emerge in other continents through aquaculture and improved transportation and distribution systems. Because of inadequate systems for routine diagnosis and monitoring or reporting for many of the zoonotic parasites, the incidence of human disease and parasite occurrence in food is underestimated. Of particular concern in industrialised countries are the highly resistant waterborne protozoal infections as well as the increased travel and immigration, which increase the exposure to exotic diseases. The increased demand for animal proteins in developing countries will lead to an intensification of the production systems in which the risk of zoonotic infections needs to be assessed. Overall, there is an urgent need for better monitoring and control of food-borne parasites using new technologies.

Development and use of a pepsin digestion method for analysis of shellfish for Cryptosporidium oocysts and Giardia cysts

Investigation of shellfish for Cryptosporidium oocysts and Giardia cysts is of public health interest because shellfish may concentrate these pathogens in their bodies, and because shellfish are frequently eaten raw or lightly cooked. To date, the methods used for the analysis of shellfish for these parasites are based on those originally designed for water concentrates or fecal samples; the reported recovery efficiencies are frequently relatively low and the amount of sample examined is small. Here, we describe the development and use of a pepsin digestion method for analyzing shellfish samples for these parasites. The conditions of the isolation method did not affect subsequent parasite detection by immunofluorescent antibody test, and allowed examination of 3-g samples of shellfish homogenate, with recovery efficiencies from blue mussel homogenates of between 70 and 80%, and similar recoveries from horse mussel and oyster homogenates. Although exposure of the parasites to the conditions used in the technique affected their viability, as assessed by vital dyes, the maximum reduction in viability after 1-h incubation in digestion solution was 20%. In a preliminary survey of shellfish collected from the Norwegian coast, Cryptosporidium oocysts were detected in blue mussel homogenates in 6 (43%) of 14 batches and Giardia cysts in 7 (50%) of these batches. However, this relatively high occurrence, compared with other surveys, may be due to the higher recovery efficiency of the new method, and the relatively large sample size analyzed. A more comprehensive study of the occurrence of these parasites in shellfish would be of pertinence to the Norwegian shellfish industry.

Molecular epidemiology of Cryptosporidium in humans and cattle in The Netherlands

The protozoan parasite Cryptosporidium is found world-wide and can cause disease in both humans and animals. To study the zoonotic potential of Cryptosporidium in The Netherlands we isolated this parasite from the faeces of infected humans and cattle and genotyped those isolates for several different markers. The overall genotyping results showed: for humans isolates, 70% Cryptosporidium hominis, 19% Cryptosporidium parvum, 10% a combination of C. hominis and C. parvum, and 1% Cryptosporidium felis; and for cattle isolates 100% C. parvum. Analysis of the genetic variants detected for the HSP70, ML1 and GP60 markers showed: for human isolates, one C. hominis and two C. parvum variants (C. parvum and C. parvum NL) for HSP70, one C. hominis and five C. parvum variants (C1, C2, C3, and C2 NL1 and C2 NL2) for ML1, four C. hominis (mainly IbA10G2) and four C. parvum variants (mainly IIaA15G2R1) for GP60; and the cattle isolates only C. parvum (not C. parvum NL1) for HSP70, C1 and C2 for ML1, and 17 different IIa sub-types (mainly IIaA15G2R1) for GP60. Molecular epidemiological analysis of the human data showed a C. hominis peak in autumn. The majority (80%) of the human cases were children aged between 0 and 9 years and >70% of these were caused by C. hominis. Patients >25 years of age were infected mainly with C. parvum. We conclude that C. hominis IbA10G2 is found at high frequencies in autumn in humans and not in cattle. The high prevalence of C. parvum IIaA15G2R1 in both humans and cattle indicates that cattle may be a reservoir for this sub-type in The Netherlands.

Maximizing recovery and detection of Cryptosporidium parvum oocysts from spiked eastern oyster (Crassostrea virginica) tissue samples

Numerous studies have documented the presence of Cryptosporidium parvum, an anthropozoonotic enteric parasite, in molluscan shellfish harvested for commercial purposes. Getting accurate estimates of Cryptosporidium contamination levels in molluscan shellfish is difficult because recovery efficiencies are dependent on the isolation method used. Such estimates are important for determining the human health risks posed by consumption of contaminated shellfish. In the present study, oocyst recovery was compared for multiple methods used to isolate Cryptosporidium parvum oocysts from oysters (Crassostrea virginica) after exposure to contaminated water for 24 h. The immunomagnetic separation (IMS) and immunofluorescent antibody procedures from Environmental Protection Agency method 1623 were adapted for these purposes. Recovery efficiencies for the different methods were also determined using oyster tissue homogenate and hemolymph spiked with oocysts. There were significant differences in recovery efficiency among the different treatment groups (P < 0.05). We observed the highest recovery efficiency (i.e., 51%) from spiked samples when hemolymph was kept separate during the homogenization of the whole oyster meat but was then added to the pellet following diethyl ether extraction of the homogenate, prior to IMS. Using this processing method, as few as 10 oocysts could be detected in a spiked homogenate sample by nested PCR. In the absence of water quality indicators that correlate with Cryptosporidium contamination levels, assessment of shellfish safety may rely on accurate quantification of oocyst loads, necessitating the use of processing methods that maximize oocyst recovery. The results from this study have important implications for regulatory agencies charged with determining the safety of molluscan shellfish for human consumption.

The potential for marine bivalve shellfish to act as transmission vehicles for outbreaks of protozoan infections in humans: a review

Most marine molluscan bivalve shellfish feed on suspended phytoplankton which are trapped from water pumped across the gills by ciliary action. Pathogenic microorganisms in the water may be filtered by the gills during feeding, and become concentrated in the digestive glands/tract. If these pathogens are not excreted or inactivated by the shellfish, or in subsequent preparatory processes, they may be ingested by consumers, the shellfish thereby acting as vehicles of infection. The protozoan parasites Cryptosporidium spp., Giardia duodenalis and Toxoplasma gondii have the potential to be transmitted in this way, and here we review the accumulating knowledge on the occurrence and survival of the transmission stages of these parasites in shellfish, whilst also emphasising the considerable gaps in our knowledge. Relevant information is particularly lacking for T. gondii, which, in comparison with Cryptosporidium spp. and G. duodenalis, has been relatively under-researched in this context. Although it seems evident that these shellfish can accumulate and concentrate all three of these parasites from the surrounding water, whether Giardia cysts remain viable and infectious is unknown, and some evidence suggests that they may be inactivated by the shellfish. Although both Toxoplasma and Cryptosporidium apparently retain their infectivity for prolonged periods in shellfish, the actual public health threat posed by these parasites via these shellfish is unclear, largely because there is minimal evidence of infection transmission. Reasons for this apparent lack of infection transmission are discussed and it is recommended that the potential for transmission via shellfish consumption is recognised by those concerned with investigating transmission of these infections.