Infections related to the ingestion of seafood Part I: viral and bacterial infections

Relationship between the contamination of gulls (Larus dominicanus) and oysters (Crassostrea gigas) with Salmonella serovar Typhimurium by PCR-RFLP

Shellfish can bioaccumulate in their tissues pathogenic contaminants present in water and they have been related with several outbreaks of food-borne diseases worldwide. With their increased population in urban areas, gulls have been reported as an important source of water environment contamination. During a 10-month period, water, gulls feces and oyster samples were collected in a shellfish harvesting site and analyzed for total and fecal coliform counts (water) and Salmonella presence (gull feces and oyster meat). Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to differentiate Salmonella species detected in gulls and oysters. Salmonella presence was detected in 3/10 of oyster samples and in 6/10 of gull feces samples by PCR. There was a relationship between Salmonella presence in oysters and fecal contamination in water. Restriction profiles of both gulls and oyster samples were similar to Salmonella Typhimurium profile by RFLP. These findings indicate strong evidence that gulls can contribute to Salmonella contamination of harvested oysters.

Detection of multiple noroviruses associated with an international gastroenteritis outbreak linked to oyster consumption

An international outbreak linked to oyster consumption involving a group of over 200 people in Italy and 127 total subjects in 13 smaller clusters in France was analyzed using epidemiological and clinical data and shellfish samples. Environmental information from the oyster-producing area, located in a lagoon in southern France, was collected to investigate the possible events leading to the contamination. Virologic analyses were conducted by reverse transcription-PCR (RT-PCR) using the same primer sets for both clinical and environmental samples. After sequencing, the data were analyzed through the database operated by the scientific network FoodBorne Viruses in Europe. The existence of an international collaboration between laboratories was critical to rapidly connect the data and to fully interpret the results, since it was not obvious that one food could be the link because of the diversity of the several norovirus strains involved in the different cases. It was also demonstrated that heavy rain was responsible for the accidental contamination of seafood, leading to a concentration of up to hundreds of genomic copies per oyster as detected by real-time RT-PCR.

Detection of human enteric viruses in shellfish collected in Tunisia

AIMS

The aim of this study was to detect the main pathogenic human RNA enteric viruses able to persist in the environment such as astrovirus, enterovirus, norovirus and hepatitis A virus (HAV) in shellfish collected from two locations in northern Tunisia.

METHODS AND RESULTS

Viruses were eluted from digestive tissues and concentrated by polyethylene glycol precipitation before nucleic acid extraction and purification. After checking for inhibitors, all viruses were detected by reverse transcription-polymerase chain reaction (RT-PCR) and confirmed by hybridization. Overall, 83% of the samples were found positive for at least one virus. Astrovirus was detected in 61% of the samples, norovirus in 35% and HAV in 26%. Surprisingly, only one sample was found positive for enterovirus.

CONCLUSIONS

The mean number of positive samples found in this study is in accordance with the data found in the literature, indicating that no real difference exists in this respect among countries studied. A notable exception is HAV, which reflects the epidemiological status of the population.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study highlights the interest to analyse shellfish samples from different production areas. These data will be helpful to understand virus circulation and to improve shellfish safety. The results, which confirm contamination, necessitate the development of appropriate studies and monitoring in all shellfish-producing countries.

Salmonella spp., Vibrio spp., Clostridium perfringens, and Plesiomonas shigelloides in marine and freshwater invertebrates from coastal California ecosystems

The coastal ecosystems of California are highly utilized by humans and animals, but the ecology of fecal bacteria at the land-sea interface is not well understood. This study evaluated the distribution of potentially pathogenic bacteria in invertebrates from linked marine, estuarine, and freshwater ecosystems in central California. A variety of filter-feeding clams, mussels, worms, and crab tissues were selectively cultured for Salmonella spp., Campylobacter spp., Escherichia coli-O157, Clostridium perfringens, Plesiomonas shigelloides, and Vibrio spp. A longitudinal study assessed environmental risk factors for detecting these bacterial species in sentinel mussel batches. Putative risk factors included mussel collection near higher risk areas for livestock or human sewage exposure, adjacent human population density, season, recent precipitation, water temperature, water type, bivalve type, and freshwater outflow exposure. Bacteria detected in invertebrates included Salmonella spp., C. perfringens, P. shigelloides, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio alginolyticus. Overall, 80% of mussel batches were culture positive for at least one of the bacterial species, although the pathogens Campylobacter, E. coli-O157, and Salmonella were not detected. Many of the same bacterial species were also cultured from upstream estuarine and riverine invertebrates. Exposure to human sewage sources, recent precipitation, and water temperature were significant risk factors for bacterial detection in sentinel mussel batches. These findings are consistent with the hypothesis that filter-feeding invertebrates along the coast concentrate fecal bacteria flowing from land to sea and show that the relationships between anthropogenic effects on coastal ecosystems and the environmental niches of fecal bacteria are complex and dynamic.

Fate of Staphylococcus aureus, Salmonella enterica serovar typhimurium, and vibrio vulnificus in raw oysters treated with chitosan

The fate of Staphylococcus aureus, Salmonella enterica serovar Typhimurium, and Vibrio vulnificus in oysters treated with chitosan was investigated. Three concentrations (0.5, 1.0, and 2.0%) of chitosan in 0.5% hydrochloric acid were prepared and coated onto raw oysters, which were then stored at 4 degrees C for 12 days. Untreated oysters and oysters coated with 0.5% hydrochloric acid without chitosan were used as controls. S. aureus cells were most sensitive to 2.0% chitosan followed by 0.5 and 1.0%. In general, chitosan treatment of oysters produced a decline in the population of S. aureus by 1 to 4 log CFU/ml compared with the untreated control. Chitosan treatment had no influence on the reduction of Salmonella Typhimurium over the 12-day storage period; inhibition of Salmonella Typhimurium growth was similar in both the control samples and the chitosan-treated samples. However, time of storage had a major effect on the survival of Salmonella Typhimurium on oysters. Neither time nor chitosan concentration had a significant effect on the growth of V. vulnificus during storage. All treatments were similar in inhibiting V. vulnificus growth.

Norwalk virus-specific binding to oyster digestive tissues

The primary pathogens related to shellfish-borne gastroenteritis outbreaks are noroviruses. These viruses show persistence in oysters, which suggests an active mechanism of virus concentration. We investigated whether Norwalk virus or viruslike particles bind specifically to oyster tissues after bioaccumulation or addition to tissue sections. Since noroviruses attach to carbohydrates of the histo-blood group family, tests using immunohistochemical analysis were performed to evaluate specific binding of virus or viruslike particles to oyster tissues through these ligands. Viral particles bind specifically to digestive ducts (midgut, main and secondary ducts, and tubules) by carbohydrate structures with a terminal N-acetylgalactosamine residue in an alpha linkage (same binding site used for recognition of human histo-blood group antigens). These data show that the oyster can selectively concentrate a human pathogen and that conventional depuration will not eliminate noroviruses from oyster tissue.

Human and animal enteric caliciviruses in oysters from different coastal regions of the United States

Food-borne diseases are a major cause of morbidity and hospitalization worldwide. Enteric caliciviruses are capable of persisting in the environment and in the tissues of shellfish. Human noroviruses (HuNoVs) have been implicated in outbreaks linked to shellfish consumption. The genetic and antigenic relatedness between human and animal enteric caliciviruses suggests that interspecies transmission may occur. To determine the occurrence of human and animal enteric caliciviruses in United States market oysters, we surveyed regional markets. Oysters were collected from 45 bays along the United States coast during the summer and winter of 2002 and 2003. Samples were analyzed by reverse transcription-PCR, and results were confirmed by hybridization and sequence analysis. Nine samples (20%) were positive for HuNoV genogroup II after hybridization. Animal enteric caliciviruses were detected in 10 samples (22%). Seven of these samples were positive for porcine norovirus genogroup II, and one sample was positive for porcine sapovirus after hybridization and confirmation by sequencing. Bovine noroviruses were detected in two samples, and these results were confirmed by sequencing. Five HuNoV samples sequenced in the polymerase region were similar to the norovirus genogroup II US 95/96 subset (genogroup II-4) previously implicated in diarrhea outbreaks. Different seasonal and state distributions were detected. The presence of animal enteric caliciviruses was associated with states with high livestock production. Although the presence of human caliciviruses in raw oysters represents a potential risk for gastroenteritis, disease confirmation by investigation of outbreaks is required. The simultaneous detection of human and animal enteric caliciviruses raises concerns about human infection or coinfection with human and animal strains that could result in genomic recombination and the emergence of new strains.

Food Safety Guidance for Older Adults

Aging is associated with loss of the physical barriers and immune efficiency that typically control pathogens' access to and multiplication within the body, thus making infection more likely in elderly persons. Chronic diseases and other health factors, such as malnutrition and immobility, may increase susceptibility to and severity of infections, including foodborne illnesses, in elderly persons, as well as associated morbidity and mortality. Prevention is the best way to avoid foodborne illnesses, but older adults have long-established food preparation and handling practices, some of which may increase the likelihood of illness. Elderly persons rely on physicians as trusted sources of health information. Physicians and other health care professionals can help prevent and control foodborne diseases by educating their patients about the risks of foodborne illness, providing sound advice on safe food-handling and consumption practices, making rapid appropriate diagnoses, and reporting cases promptly to public health authorities.

Detection of adenoviruses in shellfish by means of conventional-PCR, nested-PCR, and integrated cell culture PCR (ICC/PCR)

We tested three PCR based methodologies to detect adenoviruses associated with cultivated oysters. Conventional-PCR, nested-PCR, and integrated cell culture-PCR (ICC/PCR) were first optimized using oysters seeded with know amounts of Adenovirus serotype 5 (Ad5). The maximum sensitivity for Ad5 detection was determined for each method, and then used to detect natural adenovirus contamination in oysters from three aquiculture farms in Florianopolis, Santa Catarina State, Brazil, over a period of 6 months. The results showed that the nested-PCR was more sensitive (limit of detection: 1.2 PFU/g of tissue) than conventional-PCR and ICC-PCR (limit of detection for both: 1.2 x 10(2)PFU/g of tissue) for detection of Ad5 in oyster extracts. Nested-PCR was able to detect 90% of Ad5 contamination in harvested oyster samples, while conventional-PCR was unable to detect Ad5 in any of the samples. The present work suggests that detection of human adenoviruses can be used as a tool to monitor the presence of human viruses in marine environments where shellfish grow, and that nested-PCR is the method of choice.

Infections related to the ingestion of seafood. Part II: parasitic infections and food safety

Parasites are responsible for a substantial number of seafood-associated infections. The factor most commonly associated with infection is consumption of raw or undercooked seafood. People with underlying disorders, particularly liver disease, are more susceptible to infection. In the first part of this review, published last month, we discussed the viral and bacterial agents associated with consumption of seafood. In part II, we discuss the parasites commonly associated with seafood consumption. Parasites readily identifiable from both consumable seafood and infected human beings include nematodes, trematodes, cestodes, and protozoa. The salient features associated with seafood-related parasite infestations are discussed. To provide a safe product for consumers, the seafood industry and the government in the USA have undertaken specific measures, which include good manufacturing practices and hazards analysis and critical control points implemented by the government and regulatory agencies. Consumers should take common precautions including obtaining seafood from reputable sources especially if the seafood is to be consumed uncooked. Adequate cooking of seafood is the safest way of preventing related infections.