Vibrio bacteria in raw oysters: managing risks to human health

The human-pathogenic marine bacteria Vibrio vulnificus and V. parahaemolyticus are strongly correlated with water temperature, with concentrations increasing as waters warm seasonally. Both of these bacteria can be concentrated in filter-feeding shellfish, especially oysters. Because oysters are often consumed raw, this exposes people to large doses of potentially harmful bacteria. Various models are used to predict the abundance of these bacteria in oysters, which guide shellfish harvest policy meant to reduce human health risk. Vibrio abundance and behaviour varies from site to site, suggesting that location-specific studies are needed to establish targeted risk reduction strategies. Moreover, virulence potential, rather than simple abundance, should be also be included in future modeling efforts.     

生食贝类水产品中副溶血性弧菌的半定量风险评估

为研究上海市生食贝类水产品的食用安全性,进行了半定量风险评估。牡蛎、醉泥螺、象拔蚌、北极贝为上海市主要的生食贝类水产品,调查显示贝类水产品中副溶血性弧菌平均检出率为43.7%,其中副溶血性弧菌致病性基因Tdh+/Trh+在贝类水产品中的平均检出率为3.75%。对上海地区对生食贝类的消费情况进行了膳食调查,并利用"Risk Ranger"软件对牡蛎、醉泥螺、象拔蚌、北极贝中副溶血性弧菌进行了半定量风险评估。上海市生食贝类消费人群比例为13.86%,生食贝类的食用频率平均2.4月/餐次,平均每餐消费生食贝类水产品为49.06 g/餐。风险评估结果显示:牡蛎/副溶血性弧菌(50)属于高度风险,醉泥螺/副溶血性弧菌(46)、象拔蚌/副溶血性弧菌(44)、北极贝/副溶血性弧菌(39)均属于中度风险,根据风险排序风险大小依次为牡蛎醉泥螺象拔蚌北极贝。     

Association of antecedent malnutrition with persistent diarrhoea: a case-control study.

To determine the effect of nutritional state on persistent diarrhoea a case-control study was carried out on 756 children followed up prospectively for 18 months. Children who developed persistent diarrhoea were compared with population controls and controls with acute diarrhoea. The mean weight for age in the children with persistent diarrhoea (69.9%) was significantly lower than that in the population controls (77.0%) and the diarrhoeal controls (76.2%). Weight for age of less than or equal to 70% was associated with persistent diarrhoea in both case-control analyses (population controls, matched odds ratio 3.25; diarrhoeal controls, matched odds ratio 2.46). The corrected odds (multiple logistic regression) in the two analyses were 3.2 (95% confidence interval 1.3 to 8.1) and 3.4 (1.2 to 9.1). Weight for age of less than or equal to 70% increases the risk of persistent diarrhoea. In an underweight child there is a higher risk of diarrhoea becoming persistent. Prevention of malnutrition and intensive management of acute diarrhoea in malnourished children should help reduce the risk of the diarrhoea persisting.     

Vibrio vulnificus. Hazard on the half shell.

Vibrio vulnificus is an extremely invasive gram-negative bacillus that causes bacteremia and shock. It should be suspected in any patient who is immunocompromised or has liver disease or hemochromatosis. Reduced gastric acidity may also increase the risk of infection if a patient presents with a history of ingesting raw shellfish (especially oysters) or trauma in brackish waters and skin lesions. Patients most commonly present with one of three clinical syndromes: primary septicemia, wound infection, or gastroenteritis. Treatment includes aggressive wound debridement, antibiotic therapy, and supportive care. Rapidly diagnosing and promptly initiating therapy are critical because V vulnificus infection is rapidly progressive and mortality approaches 100% if septic shock occurs.     

Taking care of a diarrhea epidemic in an urban hospital in Bangladesh: Appraisal of putative causes,presentation, management,and deaths averted

BackgroundIn April 2018, a diarrhea epidemic broke out in Dhaka city and adjoining areas, which continued through May. The Dhaka Hospital of the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), a dedicated diarrheal disease hospital, had a large upsurge in patient visits during the epidemic. An enhanced understanding of the epidemiology of this epidemic may help health-related professionals better prepare for such events in the future. This study examined the microbial etiology and non-pathogen factors associated with diarrhea during the epidemic. The study also evaluated the patients’ presentation and clinical course and estimated the potential mortality averted by treating patients during the epidemic.Methodology/Principal findingsData from the patients who were treated at Dhaka Hospital during the diarrhea epidemic between April 2 and May 12, 2018 and were enrolled into the Diarrheal Disease Surveillance System (DDSS) at icddr,b were compared with the DDSS-enrolled patients treated during the seasonally-matched periods in the flanking years using logistic regression. icddr,b Dhaka Hospital treated 29,212 diarrheal patients during the 2018 epidemic period (and 25,950 patients per comparison period on average). Vibrio cholerae was the most common pathogen isolated (7,946 patients; 27%) and associated with diarrhea during the epidemic (adjusted odds ratio [AOR] 1.5, 95% CI: 1.1–2.0). The interaction of Vibrio cholerae with ETEC (AOR 2.7, 95% CI: 1.3–5.9) or Campylobacter (AOR 2.4, 95% CI: 1.1–5.1) was associated with further increased odds of diarrhea during the epidemic. In children under five years old, rotavirus was the most common pathogen (2,029 patients; 26%). Those who were adolescents (AOR 2.0, 95% CI: 1.3–3.1) and young adults (AOR 1.9, 95% CI: 1.4–2.5) compared to children younger than five years, resided within a 10 km radius of Dhaka Hospital (AOR 1.6, 95% CI: 1.1–2.2) compared to those living outside 20 km, borrowed money or relied on aid to pay for the transport to the hospital (AOR 1.6, 95% CI: 1.2–2.0), used tap water (AOR 1.8, 95% CI: 1.4–2.4) for drinking compared to tubewell water, and disposed of the solid waste directly outside the house (AOR 4.0, 95% CI: 2.7–5.9) were more likely to present with diarrhea during the epidemic. During the epidemic, patients were more likely to present with severe dehydration (odds ratio [OR] 1.6, 95% CI: 1.3–2.0) and require inpatient admission (OR 2.5, 95% CI: 1.9–3.3), intravenous rehydration (OR 1.7, 95% CI: 1.4–2.1), and antibiotics (OR 2.2, 95% CI: 1.8–2.7). The in-hospital case fatality rate was low (13 patients; 0.04%), and the hospital averted between 12,523 and 17,265 deaths during the epidemic.Conclusions/SignificanceVibrio cholerae played the primary role in the 2018 diarrhea epidemic in Dhaka. Campylobacter, enterotoxigenic Escherichia coli, and rotavirus had a secondary role. Adolescents and adults, residents of the metropolitan area, and those who were relatively poor and lacked safe water, sanitation, and hygiene (WASH) practices comprised the most vulnerable groups. Despite the increased disease severity during the epidemic, the case fatality rate was less than 0.1%. icddr,b Dhaka Hospital saved as many as 17,265 lives during the epidemic.     

Effectiveness of standard UV depuration at inactivating Cryptosporidium parvum recovered from spiked Pacific oysters (Crassostrea gigas)

When filter-feeding shellfish are consumed raw, because of their ability to concentrate and store waterborne pathogens, they are being increasingly associated with human gastroenteritis and have become recognized as important pathogen vectors. In the shellfish industry, UV depuration procedures are mandatory to reduce pathogen levels prior to human consumption. However, these guidelines are based around more susceptible fecal coliforms and Salmonella spp. and do not consider Cryptosporidium spp., which have significant resistance to environmental stresses. Thus, there is an urgent need to evaluate the efficiency of standard UV depuration against the survival of Cryptosporidium recovered from shellfish. Our study found that in industrial-scale shellfish depuration treatment tanks, standard UV treatment resulted in a 13-fold inactivation of recovered, viable C. parvum oocysts from spiked (1 x 10(6) oocysts liter (-1)) Pacific oysters. Depuration at half power also significantly reduced (P < 0.05; ninefold) the number of viable oocysts recovered from oysters. While UV treatment resulted in significant reductions of recovered viable oocysts, low numbers of viable oocysts were still recovered from oysters after depuration, making their consumption when raw a public health risk. Our study highlights the need for increased periodic monitoring programs for shellfish harvesting sites, improved depuration procedures, and revised microbial quality control parameters, including Cryptosporidium assessment, to minimize the risk of cryptosporidiosis.     

贝类中人源诺如病毒污染净化技术研究进展

人源诺如病毒是全球引起人急性胃肠炎的食源性病原体之一。牡蛎、贻贝等贝类消化腺组织中含有诺如病毒受体类似物,可从污染水体中富集高浓度病毒,因此,生食或食用加工不当的受污染贝类极易造成诺如病毒感染。污染贝类的净化处理技术已成为诺如病毒防控领域中的研究热点,例如消杀试剂、臭氧处理工艺、新型非热消杀技术以及最近报道的具有抗病毒作用的益生菌等。诺如病毒活性检测对确定贝类中的病毒污染水平和评价消杀技术效果有重要作用,只有完整和具有感染力的病毒才会对人体健康造成威胁。因此,本文在前期工作基础上,进一步对诺如病毒活性鉴定方法、贝类产品消杀技术以及贝类养殖净化工艺等研究进展进行综述,以期为完善食源性病毒防控技术提供参考。     

Telematics: a new tool for epidemiological surveillance of diarrhoeal diseases in the Aquitaine sentinel network.

A sentinel health information system using telematics and a network of general practitioners was set up in Aquitaine in south western France in 1986. Among the health problems under surveillance was acute diarrhoea. Data for each patient who fulfilled the usual case definition for acute diarrhoea were reported by general practitioners using home terminals (Minitels) connected to a central computer by telephone. Over one year 2234 cases of diarrhoea were reported, the incidence varying from 0.8 to 1.5 cases per doctor per week. Seasonal variations in incidence were observed, with peaks in the winter and in the summer. Only 379 (17%) episodes of diarrhoea were classified as severe, and these patients consulted their general practitioners earlier than patients whose diarrhoea was less severe. Foreign travel was rarely found in the patients'' histories, but clusters of cases were found in communities (4.6%) and in families (22.3%). The advantages of this system were easy reporting and immediate feedback, but it was difficult to extrapolate the data, and the system was inadequate for intervening in outbreaks of diarrhoeal disease. Our knowledge of diarrhoeal diseases in south west France improved.     

Virus-contaminated oysters: a three-month monitoring of oysters imported to Switzerland

Molluscan shellfish are known to be carriers of viral and bacterial pathogens. The consumption of raw oysters has been repeatedly linked to outbreaks of viral gastroenteritis and hepatitis A. Switzerland imports over 300 tons of oysters per year, 95% of which originate in France. To assess the level of viral contamination, a 3-month monitoring study was conducted. Therefore, the sensitivities of several previously described methods for virus concentration were compared, and one protocol was finally chosen by using dissected digestive tissues. Eighty-seven samples consisting of five oysters each were analyzed for Norwalk-like viruses (NLVs), enteroviruses, and hepatitis A viruses from November 2001 to February 2002. The oysters were exported by 31 French, three Dutch, and two Irish suppliers. Eight oyster samples from six French suppliers were positive for NLVs, and four samples from four French suppliers were positive for enteroviruses; two of the latter samples were positive for both viral agents. No hepatitis A viruses were detected. The sequences of NLV and enterovirus amplicons showed a great variety of strains, especially for the NLVs (strains similar to Bristol, Hawaii, Mexico, and Melksham agent). The data obtained indicated that imported oysters might be a source of NLV infection in Switzerland. However, further studies are needed to determine the quantitative significance of the risk factor within the overall epidemiology of NLVs.     

Virus-Contaminated Oysters: a Three-Month Monitoring of Oysters Imported to Switzerland

Molluscan shellfish are known to be carriers of viral and bacterial pathogens. The consumption of raw oysters has been repeatedly linked to outbreaks of viral gastroenteritis and hepatitis A. Switzerland imports over 300 tons of oysters per year, 95% of which originate in France. To assess the level of viral contamination, a 3-month monitoring study was conducted. Therefore, the sensitivities of several previously described methods for virus concentration were compared, and one protocol was finally chosen by using dissected digestive tissues. Eighty-seven samples consisting of five oysters each were analyzed for Norwalk-like viruses (NLVs), enteroviruses, and hepatitis A viruses from November 2001 to February 2002. The oysters were exported by 31 French, three Dutch, and two Irish suppliers. Eight oyster samples from six French suppliers were positive for NLVs, and four samples from four French suppliers were positive for enteroviruses; two of the latter samples were positive for both viral agents. No hepatitis A viruses were detected. The sequences of NLV and enterovirus amplicons showed a great variety of strains, especially for the NLVs (strains similar to Bristol, Hawaii, Mexico, and Melksham agent). The data obtained indicated that imported oysters might be a source of NLV infection in Switzerland. However, further studies are needed to determine the quantitative significance of the risk factor within the overall epidemiology of NLVs.     

Detection and molecular characterization of enteric viruses in environmental samples in Monastir,Tunisia between January 2003 and April 2007

Aims: A prospective study was performed to characterize the main human enteric viruses able to persist in sewage samples and in shellfish tissues, and to establish the correlation between environmental strains and viral infantile diarrhoea observed in the same area during the same period. Methods and Results: A total of 250 sewage (raw and treated) and 60 shellfish samples were collected between January 2003 and April 2007 in Monastir region, Tunisia. Group A rotavirus (RVA) was detected in 80 (32%) sewage samples, norovirus (NoV) in 11 (4·4%) and enteric adenovirus (AdV) in 1 (0·4%). Among 60 shellfish samples collected near sewage effluents, one was contaminated by NoV (1·6%). Conclusion: Our data represent the first documentation in Tunisia, combining gastroenteritis viruses circulating in the environment and in clinical isolates. We observed a correlation between environmental strains and those found in children suffering from gastroenteritis during the same period study. This suggests the existence of a relationship between water contamination and paediatric diarrhoea. Significance and Impact of the Study: Our results address the potential health risks associated with transmission of human enteric viruses through water‐related environmental routes. The research findings will aid in elucidating the molecular epidemiology and circulation of enteric viruses in Tunisia and in Africa, where data are rare.     

Case-control study of risk of dehydrating diarrhoea in infants in vulnerable period after full weaning.

OBJECTIVES: To investigate risk factors for dehydrating diarrhoea in infants, with special interest in the weaning period. DESIGN: Case-control study. SETTING: Metropolitan area of Porto Alegre, Brazil. SUBJECTS: Cases were 192 children aged 0-23 months hospitalised with acute diarrhoea and moderate to severe dehydration. Controls were 192 children matched for age and neighbourhood who did not have diarrhoea in the previous week. MAIN OUTCOME MEASURES: Associations between dehydrating diarrhoea and child''s age, type of milk consumed, time since breast feeding stopped, and breast feeding status. RESULTS: In infants aged < 12 months the risk of dehydrating diarrhoea was significantly higher in the first 9 months of life (P < 0.001), and in those aged 12-23 months the risk was again greater in younger children (12-17 months) (P = 0.03). The type of milk consumed before start of diarrhoea episode was strongly associated with dehydration independent of socioeconomic, environmental, maternal reproductive, demographic, and health services factors. Compared with infants exclusively breast fed, bottle fed infants were at higher risk (odds ratio (95% confidence interval) for cow''s milk 6.0 (1.8 to 19.8), for formula milk 6.9 (1.4 to 33.3)). Compared with those still breast feeding, children who stopped in the previous two months were more likely to develop dehydrating diarrhoea (odds ratio 8.4 (2.4 to 29.6)). This risk decreased with time since breast feeding stopped. CONCLUSION: These results confirm the protective effect of breast feeding and suggest there is a vulnerable period soon after breast feeding is stopped, which may be of relevance for developing preventive strategies.     

Pathogenesis of Vibrio vulnificus

This review describes the factors which are currently recognized as being central to the virulence of the human pathogen, Vibrio vulnificus. This estuarine/marine bacterium occurs in high numbers in molluscan shellfish, primarily oysters, and its ingestion in raw oysters results in a ca. 60% mortality in those persons who are susceptible to this bacterium. The organism is also able to produce life-threatening wound infections. We describe here the nature of both the wound and primary septicemia infections, the virulence factors known or believed to be involved in these infections, possible immunotherapy, and some thoughts on the possibility that not all strains of this pathogen are virulent.     

Effectiveness of Standard UV Depuration at Inactivating Cryptosporidium parvum Recovered from Spiked Pacific Oysters (Crassostrea gigas)

When filter-feeding shellfish are consumed raw, because of their ability to concentrate and store waterborne pathogens, they are being increasingly associated with human gastroenteritis and have become recognized as important pathogen vectors. In the shellfish industry, UV depuration procedures are mandatory to reduce pathogen levels prior to human consumption. However, these guidelines are based around more susceptible fecal coliforms and Salmonella spp. and do not consider Cryptosporidium spp., which have significant resistance to environmental stresses. Thus, there is an urgent need to evaluate the efficiency of standard UV depuration against the survival of Cryptosporidium recovered from shellfish. Our study found that in industrial-scale shellfish depuration treatment tanks, standard UV treatment resulted in a 13-fold inactivation of recovered, viable C. parvum oocysts from spiked (1 × 10⁶ oocysts liter ⁻¹) Pacific oysters. Depuration at half power also significantly reduced (P < 0.05; ninefold) the number of viable oocysts recovered from oysters. While UV treatment resulted in significant reductions of recovered viable oocysts, low numbers of viable oocysts were still recovered from oysters after depuration, making their consumption when raw a public health risk. Our study highlights the need for increased periodic monitoring programs for shellfish harvesting sites, improved depuration procedures, and revised microbial quality control parameters, including Cryptosporidium assessment, to minimize the risk of cryptosporidiosis.     

Real-Time PCR Assays for Quantification and Differentiation of Vibrio vulnificus Strains in Oysters and Water

Vibrio vulnificus is an autochthonous estuarine bacterium and a pathogen that is frequently transmitted via raw shellfish. Septicemia can occur within 24 h; however, isolation and confirmation from water and oysters require days. Real-time PCR assays were developed to detect and differentiate two 16S rRNA variants, types A and B, which were previously associated with environmental sources and clinical fatalities, respectively. Both assays could detect 10² to 10³ V. vulnificus total cells in seeded estuarine water and in oyster homogenates. PCR assays on 11 reference V. vulnificus strains and 22 nontarget species gave expected results (type A or B for V. vulnificus and negative for nontarget species). The relationship between cell number and cycle threshold for the assays was linear (R² = >0.93). The type A/B ratio of Florida clinical isolates was compared to that of isolates from oysters harvested in Florida waters. This ratio was 19:17 in clinical isolates and 5:8 (n = 26) in oysters harvested from restricted sites with poor water quality but was 10:1 (n = 22) in oysters from permitted sites with good water quality. A substantial percentage of isolates from oysters (19.4%) were type AB (both primer sets amplified), but no isolates from overlying waters were type AB. The real-time PCR assays were sensitive, specific, and quantitative in water samples and could also differentiate the strains in oysters without requiring isolation of V. vulnificus and may therefore be useful for rapid detection of the pathogen in shellfish and water, as well as further investigation of its population dynamics.     

Accumulation of sediment-associated viruses in shellfish

The present study focused on the importance of contaminated sediments in shellfish accumulation of human viruses. Epifaunal (Crassostrea virginica) and infaunal (Mercenaria mercenaria) shellfish, placed on or in cores, were exposed to either resuspended or undisturbed sediments containing bound poliovirus type 1 (LSc 2ab). Consistent bioaccumulation by oysters (four of five trials) was only noted when sediment-bound viruses occurred in the water column. Virus accumulation was observed in a single instance where sediments remained in an undisturbed state. While the incidence of bioaccumulation was higher with resuspended rather than undisturbed contaminated sediment, the actual concentration of accumulated viruses was not significantly different. The accumulation of viruses from oysters residing on uninoculated sediments. When clams were exposed to undisturbed, virus-contaminated sediments, two of five shellfish pools yielded viral isolates. Bioaccumulation of undisturbed sediments by these bivalves was considered marginal when related to the concentration of virus in contaminated sediments; they would only represent a significant threat when suspended in the water column. Arguments were advanced for water-column sampling in the region of the water-sediment interface to provide an accurate determination of the virological quality of shellfish harvesting waters.     

Accumulation of sediment-associated viruses in shellfish.

The present study focused on the importance of contaminated sediments in shellfish accumulation of human viruses. Epifaunal (Crassostrea virginica) and infaunal (Mercenaria mercenaria) shellfish, placed on or in cores, were exposed to either resuspended or undisturbed sediments containing bound poliovirus type 1 (LSc 2ab). Consistent bioaccumulation by oysters (four of five trials) was only noted when sediment-bound viruses occurred in the water column. Virus accumulation was observed in a single instance where sediments remained in an undisturbed state. While the incidence of bioaccumulation was higher with resuspended rather than undisturbed contaminated sediment, the actual concentration of accumulated viruses was not significantly different. The accumulation of viruses from oysters residing on uninoculated sediments. When clams were exposed to undisturbed, virus-contaminated sediments, two of five shellfish pools yielded viral isolates. Bioaccumulation of undisturbed sediments by these bivalves was considered marginal when related to the concentration of virus in contaminated sediments; they would only represent a significant threat when suspended in the water column. Arguments were advanced for water-column sampling in the region of the water-sediment interface to provide an accurate determination of the virological quality of shellfish harvesting waters.     

Inefficient accumulation of low levels of monodispersed and feces-associated poliovirus in oysters.

The accumulation of low levels (0.002 to 0.18 PFU/ml) of both feces-associated and monodispersed poliovirus by oysters (Crassostrea virginica or C. gigas) and clams (Mercenaria mercenaria) was investigated. These levels were chosen to duplicate the conditions present in light to moderately polluted waters. Experiments were performed in both small- and large-scale flowing seawater systems, developed to mimic the natural marine habitats of shellfish. Under these experimental conditions, viral accumulation by physiologically active shellfish was only noted when water column concentrations exceeded approximately 0.01 PFU/ml. Bioaccumulation increased with increasing concentrations of both monodispersed and feces-associated viruses. At virus concentrations below this level, viruses were seldom detected in either clams or oysters. Evidence indicated that the lack of accumulation was not the result of inefficient extraction or detection methods. The modified Cat-Floc-beef extract procedure used in the experiment was found to be capable of detecting as few as 1.5 to 2.0 PFU per shellfish. Evidence is presented to indicate that an uptake-depuration equilibrium was present at virus exposure levels of 0.10 PFU/ml, but not at 0.01 PFU/ml. The results suggested that viral accumulation by shellfish may not be efficient at water column concentrations below congruent to 0.01 PFU/ml.     

Assessment of Human Health Risks of Consumption of Cadmium Contaminated Cultured Oysters

With farmed British Columbia (BC) oysters containing higher cadmium concentrations than wild oysters, long-term exposure to cadmium through consumption of oysters has the potential to cause health risks. This study reports on a risk assessment for cadmium intake resulting from the consumption of BC-cultured oyster. The study concludes that Health Canada's current recommended BC-cultured oyster consumption rate for Canadians of 12 oysters per month exceeds the Agency for Toxic Substances and Disease Registry chronic oral minimal risk levels (MRL) of 0.2 μ g·kg^{? 1}·day^{? 1} by approximately 4-to 5-fold and reaches the Food and Agriculture Organization/World Health Organization (FAP/WHO) reference dose of 1 μg·kg^?1·day^?1 for cadmium consumption for Canadians. This suggests that although the current recommended maximum oyster consumption rates is consistent with the FAO/WHO and U.S. Environmental Protection Agency limits for acceptable risk, it leaves little or no room for error or uncertainty. This is noteworthy as recent studies demonstrate toxicological effects at cadmium intakes of 0.43 to 0.71 μ gCd·kg^?1·day^?1. This study indicates that a lower maximum BC-cultured oyster rate should be considered, particularly for high risk groups, including women with low iron stores, people with renal impairment, smokers, children, and indigenous people who consume organ meats of games and wildlife other than shellfish.     

Identification of tdh-positive Vibrio parahaemolyticus from an outbreak associated with raw oyster consumption in Spain

Between August and September 1999, a total of 64 cases of illness were identified in three episodes of acute gastroenteritis associated with the consumption of live oysters from a typical outdoor street market in Galicia (northwest Spain). Nine case patients were hospitalized and analysis of their stool samples revealed the presence of Vibrio parahaemolyticus. The strains isolated from two stool samples were studied for antibiotic susceptibility, biochemical characteristics and presence of virulence factors. Both isolates were Kanagawa phenomenon positive and produced thermostable direct hemolysin, which is related to pathogenicity in humans. These results show the presence of pathogenic V. parahaemolyticus in mollusks harvested in Europe and reveal the risk of illness associated with their consumption, suggesting the revision of V. parahaemolyticus risk assessment associated with consumption of raw live shellfish.