Aflatoxin M1 in milk does not contribute substantially to global liver cancer incidence

BACKGROUND

For 60 y, it has been known that aflatoxin B1 (AFB1), a mycotoxin produced by Aspergillus fungi in certain food and feed crops, causes hepatocellular carcinoma (liver cancer; HCC) in humans. The annual global burden of AFB1-related HCC has been estimated. However, much less is known about the potential carcinogenic impact of a metabolite of AFB1 called aflatoxin M1 (AFM1), which is secreted in milk when dairy animals consume AFB1-contaminated feed. The cancer risk of AFM1 to humans from milk consumption has not yet been evaluated.

OBJECTIVES

We sought to estimate the global risk of AFM1-related liver cancer through liquid milk consumption, accounting for possible synergies between AFM1 and chronic infection with hepatitis B virus (HBV) in increasing cancer risk.

METHODS

We conducted a quantitative cancer risk assessment by analyzing extensive datasets of national population sizes, dairy consumption patterns, AFM1 concentrations in milk in 40 nations, and chronic HBV prevalence. Two separate cancer risk assessments were conducted: assuming a possible synergy between AFM1 and HBV in increasing cancer risk in a manner similar to that of AFB1 and HBV, and assuming no such synergy.

RESULTS

If there is no synergy between AFM1 and HBV, AFM1 may contribute ∼0.001% of total annual HCC cases globally. If there is synergy between AFM1 and HBV infection, AFM1 may contribute ∼0.003% of all HCC cases worldwide. In each case, the total expected AFM1-attributable cancer cases are ∼13-32 worldwide.

CONCLUSION

AFM1 exposure through liquid milk consumption does not substantially increase liver cancer risk in humans. Policymakers should consider this low risk against the nutritional benefits of milk consumption, particularly to children, in a current global situation of milk being discarded because of AFM1 concentrations exceeding regulatory standards.

Global Burden of Animal Diseases: a novel approach to understanding and managing disease in livestock and aquaculture

Investments in animal health and Veterinary Services can have a measurable impact on the health of people and the environment. These investments require a baseline metric that describes the burden of animal health and welfare in order to justify and prioritise resource allocation and from which to measure the impact of interventions. This paper is part of a process of scientific enquiry in which problems are identified and solutions sought in an inclusive way. It poses the broad question: what should a system to measure the animal disease burden on society look like and what value would it add? Moreover, it aims to do this in such a way as to be accessible by a wide audience, who are encouraged to engage in this debate. Given that farmed animals, including those raised by poor smallholders, are an economic entity, this system should be based on economic principles. These poor farmers are negatively impacted by disparities in animal health technology, which can be addressed through a mixture of supply-led and demand-driven interventions, reinforcing the relevance of targeted financial support from government and non-governmental organisations. The Global Burden of Animal Diseases (GBADs) Programme will glean existing data to measure animal health losses within carefully characterised production systems. Consistent and transparent attribution of animal health losses will enable meaningful comparisons of the animal disease burden to be made between diseases, production systems and countries, and will show how it is apportioned by people's socio-economic status and gender. The GBADs Programme will produce a cloud-based knowledge engine and data portal, through which users will access burden metrics and associated visualisations, support for decisionmaking in the form of future animal health scenarios, and the outputs of wider economic modelling. The vision of GBADs, strengthening the food system for the benefit of society and the environment, is an example of One Health thinking in action.

Community engagement and building trust to resolve ethical challenges during humanitarian crises: experience from the CAGED study

Background

According to the Internal Displacement Monitoring Centre report on global human displacement, Ethiopia has the highest number of newly displaced people forced to flee their homes. Displaced people have arrived in other regions, sometimes leading to conflict. Several regions in Ethiopia experience on-going ethnic tensions and violence between tribes, which leaves smallholder farmers suspicious of any outside activities in their locale, assuming other ethnic groups may harm them. Changes in the central Ethiopian government have also led to suspicion of non-local agencies. The Campylobacter Genomics and Enteric Dysfunction (CAGED) research project's objective is to improve the incomes, livelihoods and nutrition of smallholder farmers and was conducted during this period of increasing violence. The project aims to assess the impact of reducing exposure to chicken excreta on young children's gut health and growth. This paper does not report empirical findings from CAGED, but is part of a series that aims to identify challenges in humanitarian research and reports on mitigation strategies during this research.

Discussion

This research is important to determine whether Campylobacter infection in chicken's contributes to illness and stunting in children. However, violence against other researchers in different parts of Ethiopia led to mistrust and lack of engagement by the community with the researchers. Some reactions were so hostile that the team was fearful about returning to some households. As a result, the team designed strategies to respond, including establishing two types of community advisory boards. One used pre-existing village elder structures and another was composed of village youth. Data collection team members received training in principles of ethics, consent, and crisis management, and were provided on-going support from local and international principal investigators and the study's ethics advisor.

Conclusion

The hostility and mistrust led to fear among the data collectors. These and the resulting strategies to address them resulted in delays for the research. However, the interventions taken resulted in successful completion of the field activities. Moreover, the lessons learned from this project are already being implemented with other projects being conducted in various parts of Ethiopia.

111 Awardee Talk - Sustainable diets must include animal-source foods

The notion that consuming animal-source food (ASF; milk, meat, fish and eggs) is incompatible with sustainable development is flawed. Negative perceptions of livestock consumption in many sustainability debates arise from a focus on overconsumption of ASF, particularly in middle to high-income countries, and a narrow interpretation of sustainability that focuses only one, albeit important, indicator — climate change. However, for the almost 800 million extremely poor people who live on less than $1.90/day and subsist on a diet heavily based on starchy foods, more — not less — ASF will be required for sustainable development, as they provide key nutrients required for full human development. Childhood stunting rates and the associated reductions in health, cognitive development, and economic productivity are rampant in countries with low levels of ASF consumption. Yet these foods are the best sources of high-quality nutrient-rich food for children aged 6 to 23 months according to the World Health Organization, and may be the only source of some. Compared to plant foods, ASF supply greater quantities of higher quality protein and more bioavailable vitamin A, vitamin D3, iron, iodine, zinc, calcium and folic acid among other nutrients, and they are the only natural source of vitamin B12, deficiency of which is associated with developmental disorders, anemia, poorer cognitive function, and lower motor development. Therefore, consumption of ASF by the poor should be prioritized to prevent the devastating, lifelong and intergenerational effects of stunting. Consumption of ASF is also important in developed countries to reduce consumption of “empty” calories that contribute to obesity and to meet specific nutrient needs. Sustainable intensification of ASF production addresses the need to improve livestock productivity, reduce greenhouse gas emissions from livestock systems while feeding the world and specifically meeting the growing global demand for ASF, which is expected to double by 2050.

Validation of a Restructured Beef Jerky Product and Process to Reduce Pathogen Loads and Improve Shelf Stability in Ethiopia

ObjectivesAnimal-sourced foods (ASFs), such as meat, provide nutrients that are beneficial for physical and cognitive development, especially in developing countries. Despite Ethiopia containing Africa’s largest inventory of livestock, market structure and inefficiencies in livestock and meat industries contribute to low-per capita consumption of meat. The combination of extensive periods of fasting from ASFs, knowledge gaps in hygienic handling and sanitation, lack of infrastructure and preservation, and weakly enforced food safety regulations contribute food safety risks in an already protein-deficient population. The objective of this study is to develop a dried beef jerky procedure that will reduce pathogen loads in meat, improve shelf stability, and increase access to ASFs in Ethiopia.Materials and MethodsChallenge studies were performed to validate a restructured jerky production process for control of five serotypes of Salmonella enterica (Saint Paul, Anatum, Typhimurium, Newport, Dublin) and three strains of E. coli O157:H7, within the constraints of equipment and ingredients available in Ethiopia. A traditional Ethiopian spice mixture was added to lean ground beef (94% lean, 6% fat), and in separate trials apple cider vinegar and pureed raisins were incorporated at varying percentages of the overall weight. The ground meat mixture was formed into strips and dehydrated to achieve aw of less than 0.70 for shelf stability and samples were plated for enumeration before and after drying. A consumer taste panel was conducted with treatments (0% and 15% raisin inclusion) to determine the acceptability of Ethiopian consumers. Sixteen Ethiopian consumers (10 men and 6 women) were asked to answer study-related questions and evaluate jerky products on visual appeal, texture, off-flavor, and overall liking on a 10-point hedonic scale.ResultsVinegar inclusion negatively impacted log CFU reductions of S. enterica as the control demonstrated significantly higher (P = 0.04) reductions than treatments including vinegar at 0.5, 1, and 2%. Including 15% raisins (w/w) in the meat and spice mixture resulted in an increased (P < 0.0001) log CFU reduction of S. enterica (5.41 CFU/g) versus the control (4.44 CFU/g) and all treatments achieved greater than 6-log CFU/g reduction of E. coli O157:H7.ConclusionIncluding raisins reduces S. enterica loads versus the control and all formulations exceeded a 6.0 log CFU/g reduction of E. coli O157:H7, in a restructured beef jerky product. A restructured jerky product could provide butchers with an additional marketing avenue and opportunity to reduce waste and pathogen loads in beef. Ethiopian consumers would also have an option for a commercially available, shelf-stable product which could provide additional protein to their diet that is easy to store and transport.

One Health - Cycling of diverse microbial communities as a connecting force for soil, plant, animal, human and ecosystem health

The One Health concept proposes that there is a connection between human, animal and environmental health. Plants and their health are not explicitly included. In this review, we broaden the One Health concept to include soil, plant, animal and ecosystem health. We argue that the health conditions of all organisms in an ecosystem are interconnected through the cycling of subsets of microbial communities from the environment (in particular the soil) to plants, animals and humans, and back into the environment. After an introduction on health concepts, we present examples of community stability and resilience, diversity and interconnectedness as affected by pollutants, and integrity of nutrient cycles and energy flows. Next, we explain our concept of microbial cycling in relation to ecosystem health, and end with examples of plant and animal disease outbreaks in relation to microbial community composition and diversity. We conclude that we need a better understanding of the role of interconnected microbiomes in promoting plant and animal health and possible ways to stimulate a healthy, diverse microbiome throughout human-dominated ecosystems. We suggest that it is essential to maintain ecosystem and soil health through diversification of plant communities and oligotrophication of managed ecosystems.

Attribution of global foodborne disease to specific foods: Findings from a World Health Organization structured expert elicitation

BACKGROUND

Recently the World Health Organization, Foodborne Disease Burden Epidemiology Reference Group (FERG) estimated that 31 foodborne diseases (FBDs) resulted in over 600 million illnesses and 420,000 deaths worldwide in 2010. Knowing the relative role importance of different foods as exposure routes for key hazards is critical to preventing illness. This study reports the findings of a structured expert elicitation providing globally comparable food source attribution estimates for 11 major FBDs in each of 14 world subregions.

METHODS AND FINDINGS

We used Cooke's Classical Model to elicit and aggregate judgments of 73 international experts. Judgments were elicited from each expert individually and aggregated using both equal and performance weights. Performance weighted results are reported as they increased the informativeness of estimates, while retaining accuracy. We report measures of central tendency and uncertainty bounds on food source attribution estimate. For some pathogens we see relatively consistent food source attribution estimates across subregions of the world; for others there is substantial regional variation. For example, for non-typhoidal salmonellosis, pork was of minor importance compared to eggs and poultry meat in the American and African subregions, whereas in the European and Western Pacific subregions the importance of these three food sources were quite similar. Our regional results broadly agree with estimates from earlier European and North American food source attribution research. As in prior food source attribution research, we find relatively wide uncertainty bounds around our median estimates.

CONCLUSIONS

We present the first worldwide estimates of the proportion of specific foodborne diseases attributable to specific food exposure routes. While we find substantial uncertainty around central tendency estimates, we believe these estimates provide the best currently available basis on which to link FBDs and specific foods in many parts of the world, providing guidance for policy actions to control FBDs.

World Health Organization Estimates of the Global and Regional Disease Burden of 11 Foodborne Parasitic Diseases, 2010: A Data Synthesis

BACKGROUND

Foodborne diseases are globally important, resulting in considerable morbidity and mortality. Parasitic diseases often result in high burdens of disease in low and middle income countries and are frequently transmitted to humans via contaminated food. This study presents the first estimates of the global and regional human disease burden of 10 helminth diseases and toxoplasmosis that may be attributed to contaminated food.

METHODS AND FINDINGS

Data were abstracted from 16 systematic reviews or similar studies published between 2010 and 2015; from 5 disease data bases accessed in 2015; and from 79 reports, 73 of which have been published since 2000, 4 published between 1995 and 2000 and 2 published in 1986 and 1981. These included reports from national surveillance systems, journal articles, and national estimates of foodborne diseases. These data were used to estimate the number of infections, sequelae, deaths, and Disability Adjusted Life Years (DALYs), by age and region for 2010. These parasitic diseases, resulted in 48.4 million cases (95% Uncertainty intervals [UI] of 43.4-79.0 million) and 59,724 (95% UI 48,017-83,616) deaths annually resulting in 8.78 million (95% UI 7.62-12.51 million) DALYs. We estimated that 48% (95% UI 38%-56%) of cases of these parasitic diseases were foodborne, resulting in 76% (95% UI 65%-81%) of the DALYs attributable to these diseases. Overall, foodborne parasitic disease, excluding enteric protozoa, caused an estimated 23.2 million (95% UI 18.2-38.1 million) cases and 45,927 (95% UI 34,763-59,933) deaths annually resulting in an estimated 6.64 million (95% UI 5.61-8.41 million) DALYs. Foodborne Ascaris infection (12.3 million cases, 95% UI 8.29-22.0 million) and foodborne toxoplasmosis (10.3 million cases, 95% UI 7.40-14.9 million) were the most common foodborne parasitic diseases. Human cysticercosis with 2.78 million DALYs (95% UI 2.14-3.61 million), foodborne trematodosis with 2.02 million DALYs (95% UI 1.65-2.48 million) and foodborne toxoplasmosis with 825,000 DALYs (95% UI 561,000-1.26 million) resulted in the highest burdens in terms of DALYs, mainly due to years lived with disability. Foodborne enteric protozoa, reported elsewhere, resulted in an additional 67.2 million illnesses or 492,000 DALYs. Major limitations of our study include often substantial data gaps that had to be filled by imputation and suffer from the uncertainties that surround such models. Due to resource limitations it was also not possible to consider all potentially foodborne parasites (for example Trypanosoma cruzi).

CONCLUSIONS

Parasites are frequently transmitted to humans through contaminated food. These estimates represent an important step forward in understanding the impact of foodborne diseases globally and regionally. The disease burden due to most foodborne parasites is highly focal and results in significant morbidity and mortality among vulnerable populations.

Modelling the species jump: towards assessing the risk of human infection from novel avian influenzas

The scientific understanding of the driving factors behind zoonotic and pandemic influenzas is hampered by complex interactions between viruses, animal hosts and humans. This complexity makes identifying influenza viruses of high zoonotic or pandemic risk, before they emerge from animal populations, extremely difficult and uncertain. As a first step towards assessing zoonotic risk of influenza, we demonstrate a risk assessment framework to assess the relative likelihood of influenza A viruses, circulating in animal populations, making the species jump into humans. The intention is that such a risk assessment framework could assist decision-makers to compare multiple influenza viruses for zoonotic potential and hence to develop appropriate strain-specific control measures. It also provides a first step towards showing proof of principle for an eventual pandemic risk model. We show that the spatial and temporal epidemiology is as important in assessing the risk of an influenza A species jump as understanding the innate molecular capability of the virus. We also demonstrate data deficiencies that need to be addressed in order to consistently combine both epidemiological and molecular virology data into a risk assessment framework.

Trend analysis of Trichinella in a red fox population from a low endemic area using a validated artificial digestion and sequential sieving technique

Freezing of fox carcasses to minimize professional hazard of infection with Echinococcus multilocularis is recommended in endemic areas, but this could influence the detection of Trichinella larvae in the same host species. A method based on artificial digestion of frozen fox muscle, combined with larva isolation by a sequential sieving method (SSM), was validated using naturally infected foxes from Latvia. The validated SSM was used to detect dead Trichinella muscle larvae (ML) in frozen muscle samples of 369 red foxes from the Netherlands, of which one fox was positive (0.067 larvae per gram). This result was compared with historical Trichinella findings in Dutch red foxes. Molecular analysis using 5S PCR showed that both T. britovi and T. nativa were present in the Latvian foxes, without mixed infections. Of 96 non-frozen T. britovi ML, 94% was successfully sequenced, whereas this was the case for only 8.3% of 72 frozen T. britovi ML. The single Trichinella sp. larva that was recovered from the positive Dutch fox did not yield PCR product, probably due to severe freeze-damage. In conclusion, the SSM presented in this study is a fast and effective method to detect dead Trichinella larvae in frozen meat. We showed that the Trichinella prevalence in Dutch red fox was 0.27% (95% CI 0.065-1.5%), in contrast to 3.9% in the same study area fifteen years ago. Moreover, this study demonstrated that the efficacy of 5S PCR for identification of Trichinella britovi single larvae from frozen meat is not more than 8.3%.

The global burden of listeriosis: a systematic review and meta-analysis

BACKGROUND

Listeriosis, caused by Listeria monocytogenes, is an important foodborne disease that can be difficult to control and commonly results in severe clinical outcomes. We aimed to provide the first estimates of global numbers of illnesses, deaths, and disability-adjusted life-years (DALYs) due to listeriosis, by synthesising information and knowledge through a systematic review.

METHODS

We retrieved data on listeriosis through a systematic review of peer-reviewed and grey literature (published in 1990-2012). We excluded incidence data from before 1990 from the analysis. We reviewed national surveillance data where available. We did a multilevel meta-analysis to impute missing country-specific listeriosis incidence rates. We used a meta-regression to calculate the proportions of health states, and a Monte Carlo simulation to generate DALYs by WHO subregion.

FINDINGS

We screened 11,722 references and identified 87 eligible studies containing listeriosis data for inclusion in the meta-analyses. We estimated that, in 2010, listeriosis resulted in 23,150 illnesses (95% credible interval 6061-91,247), 5463 deaths (1401-21,497), and 172,823 DALYs (44,079-676,465). The proportion of perinatal cases was 20·7% (SD 1·7).

INTERPRETATION

Our quantification of the global burden of listeriosis will enable international prioritisation exercises. The number of DALYs due to listeriosis was lower than those due to congenital toxoplasmosis but accords with those due to echinococcosis. Urgent efforts are needed to fill the missing data in developing countries. We were unable to identify incidence data for the AFRO, EMRO, and SEARO WHO regions.

FUNDING

WHO Foodborne Diseases Epidemiology Reference Group and the Université catholique de Louvain.

Cost of illness and disease burden in The Netherlands due to infections with Shiga toxin-producing Escherichia coli O157

Infections with Shiga toxin-producing Escherichia coli O157 (STEC O157) are associated with hemorrhagic colitis, hemolytic uremic syndrome (HUS), and end-stage renal disease (ESRD). In the present study, we extend previous estimates of the burden of disease associated with STEC O157 with estimates of the associated cost of illness in The Netherlands. A second-order stochastic simulation model was used to calculate disease burden as disability-adjusted life years (DALYs) and cost of illness (including direct health care costs and indirect non-health care costs). Future burden and costs are presented undiscounted and discounted at annual percentages of 1.5 and 4%, respectively. Annually, approximately 2.100 persons per year experience symptoms of gastroenteritis, leading to 22 cases of HUS and 3 cases of ESRD. The disease burden at the population level was estimated at 133 DALYs (87 DALYs discounted) per year. Total annual undiscounted and discounted costs of illness due to STEC O157 infection for the Dutch society were estimated at €9.1 million and €4.5 million, respectively. Average lifetime undiscounted and discounted costs per case were both €126 for diarrheal illness, both €25,713 for HUS, and €2.76 million and €1.22 million, respectively, for ESRD. The undiscounted and discounted costs per case of diarrheal disease including sequelae were €4,132 and €2,131, respectively. Compared with other foodborne pathogens, STEC O157 infections result in relatively low burden and low annual costs at the societal level, but the burden and costs per case are high.

Probabilistic inversion in priority setting of emerging zoonoses

This article presents methodology of applying probabilistic inversion in combination with expert judgment in priority setting problem. Experts rank scenarios according to severity. A linear multi-criteria analysis model underlying the expert preferences is posited. Using probabilistic inversion, a distribution over attribute weights is found that optimally reproduces the expert rankings. This model is validated in three ways. First, consistency of expert rankings is checked, second, a complete model fitted using all expert data is found to adequately reproduce observed expert rankings, and third, the model is fitted to subsets of the expert data and used to predict rankings in out-of-sample expert data.

Attributing the human disease burden of foodborne infections to specific sources

Foodborne diseases are an important cause of human illness worldwide. Humans acquire these infections from a variety of sources and routes of transmission. Many efforts have been made in the last decades to prevent and control foodborne diseases, particularly foodborne zoonoses. However, information on the impact of these interventions is limited. To identify and prioritize successful food safety interventions, it is important to attribute the burden of human illness to the specific sources. Defining scientific concepts and harmonizing terminology for "source attribution" is essential for understanding and improving attribution methodologies and for sharing knowledge within the scientific community. We propose harmonized nomenclature, and describe the various approaches for human illness source attribution and their usefulness to address specific public health questions.

Dose response for infectivity of several strains of Campylobacter jejuni in chickens

Although some major risk studies have been done for Campylobacter jejuni, its dose response is not well characterized. Only a single human study is available, providing dose-response information for only a single isolate. As substantial heterogeneity in infectivity has been acknowledged for other pathogens, it remains unknown how well this single study represents the dose-response relation for this pathogen. As future human challenge studies with Campylobacter are unlikely, we have to find other means of studying its infectivity. Several dose-response studies have been done using chickens as host organisms. These studies may be used to obtain quantitative information on the variation in infectivity among different isolates of this pathogen. A hierarchical Bayesian model is well suited to describe heterogeneity, and we demonstrate how the beta-Poisson model of microbial infection may be adapted to allow for within- and between-isolate variation. Isolates tested in chickens can be categorized into two distinct groups: lab-adapted and fresh isolates, and we show how the hierarchical dose-response model can be used to quantitatively describe their differences. Fresh isolates show higher colonization potential and less within-isolate variation than lab isolates. The results indicate that Campylobacter jejuni is highly infectious in chickens. Different isolates show great variation in infectivity, especially between lab and fresh isolates, indicating that human clinical (volunteer) studies on infectivity must be interpreted cautiously.

A poultry-processing model for quantitative microbiological risk assessment

A poultry-processing model for a quantitative microbiological risk assessment (QMRA) of campylobacter is presented, which can also be applied to other QMRAs involving poultry processing. The same basic model is applied in each consecutive stage of industrial processing. It describes the effects of inactivation and removal of the bacteria, and the dynamics of cross-contamination in terms of the transfer of campylobacter from the intestines to the carcass surface and the environment, from the carcasses to the environment, and from the environment to the carcasses. From the model it can be derived that, in general, the effect of inactivation and removal is dominant for those carcasses with high initial bacterial loads, and cross-contamination is dominant for those with low initial levels. In other QMRA poultry-processing models, the input-output relationship between the numbers of bacteria on the carcasses is usually assumed to be linear on a logarithmic scale. By including some basic mechanistics, it is shown that this may not be realistic. As nonlinear behavior may affect the predicted effects of risk mitigations; this finding is relevant for risk management. Good knowledge of the variability of bacterial loads on poultry entering the process is important. The common practice in microbiology to only present geometric mean of bacterial counts is insufficient: arithmetic mean are more suitable, in particular, to describe the effect of cross-contamination. The effects of logistic slaughter (scheduled processing) as a risk mitigation strategy are predicted to be small. Some additional complications in applying microbiological data obtained in processing plants are discussed.

Release kinetics and cell trafficking in relation to bacterial growth explain the time course of blood neutrophils and monocytes during primary Salmonella infection

Granulocytes and neutrophils are predominantly responding cells during the early phase of infection of rats with Salmonella. We propose mathematical and experimental models of the kinetics of neutrophil and monocyte responses in Salmonella infection via the oral route. Using the models, we estimate that approximately 1 in 500 inoculated Salmonella cells actually infected the rat and multiplied with a doubling time of 5 h in Peyer's patches, reaching a maximum of approximately 10(6) c.f.u./g. In low-dose infection, neutrophil and monocyte responses are delayed, but further resemble the responses in high-dose infection. Important processes influencing neutrophil and monocyte recruitment are: massive migration into the infected tissue, and non-linear release kinetics of neutrophils and monocytes from the bone marrow. In conclusion, we can predict time series of neutrophil and monocyte responses in low-dose and high-dose experimental infection via the oral route.

Intraspecies variability in the dose-response relationship for Salmonella Enteritidis associated with genetic differences in cellular immune response

To evaluate the effects of differences in host cellular immunity, we studied the dose-response relationship for infection with Salmonella enterica serovar Enteritidis (SE) in two different rat strains, skewed towards T helper 1 (Th1, Lewis rats) or T helper 2 (Th2, Brown Norway rats) immunoregulation. Rats were exposed orally to different doses of SE after overnight starvation and neutralization of gastric acid. Animals were observed for clinical signs of disease, fecal excretion and SE load in spleen and cecum, histopathology of the cecum, hematology, and cellular and humoral immune responses. Exponential dose-response models were used for binary or continuous outcomes to analyze the experimental data. Cytokine patterns, antibody isotypes, and contact hypersensitivity tests confirmed that Lewis rats are Th1 prone, whereas Brown Norway rats are Th2 prone. The probability of infection per single SE cell was approximately 100 times higher in Brown Norway rats than in Lewis rats. Cellular immune responses were more pronounced in Lewis rats but antibody responses were higher in Brown Norway rats. When infected, colonization levels and inflammation are highest in the intestinal tract of Th2 skewed rats, but systemic infection is more intense in Th1 skewed rats. Successful colonization by only one or two SE clones resulted in a marked increase of neutrophil counts by a factor of two to three in both rat strains.

Occurrence and levels of indicator bacteriophages in bathing waters throughout Europe

Somatic coliphages, F-specific RNA bacteriophages, bacteriophages infecting Bacteroides fragilis, Escherichia coli and enterococci were counted in bathing waters in the late spring and summer. We tested fresh and marine bathing waters from North, South, East and West Europe expected to contain between 100 and 500 E. coli per 100 ml, although wider ranges were sometimes found. Bacteriophages were counted after concentration, since a preliminary study proved that this step was necessary to obtain positive counts. During monitoring, a first-line quality control with reference materials for bacteria and bacteriophages was performed by all the laboratories participating in the study. The same microbes were also counted in raw sewage samples from various areas in Europe, where the bacterial indicators and the three groups of bacteriophages were detected in roughly the same numbers. All groups of bacteriophages were detected in both fresh and marine bathing waters throughout Europe. Reliable and complete results from 147 samples showed that for log-transformed values, E. coli and bacteriophages were slightly correlated. However, the slope of the regression line changed according to E. coli concentration and the correlation diminished when this concentration was close to zero per 100 ml. The ratios between E. coli and phages in bathing waters differed significantly from those in sewage. The relative amounts of bacteriophages, mainly somatic coliphages and phages infecting Bact. fragilis RYC2056, increased in bathing waters with low E. coli concentration, especially in seawater samples containing < 100 E. coli per 100 ml. The relationship of bacteriophages with respect to enterococci paralleled that of bacteriophages with respect to E. coli. Somatic coliphages and bacteriophages infecting Bact. fragilis are useful to predict the presence of some pathogens with the same origin as present bacterial indicators but with higher survival rates.

A quantitative model for neutrophil response and delayed-type hypersensitivity reaction in rats orally inoculated with various doses of Salmonella Enteritidis

Our aim was to investigate the quantitative relationship between inoculation doses and physiological responses to infection by Salmonella enterica serovar Enteritidis. Rats were orally inoculated with 10-10(9) c.f.u. of S. Enteritidis and monitored for 6 days. Neutrophil and delayed-type hypersensitivity (DTH) responses were assessed, and the spleens were analyzed for the pathogen. The experimental data were analyzed by a mathematical model for the host response to salmonella infection, which is based on the assumptions that: (i) the number of pathogens in the inoculum is Poisson distributed, (ii) any cell that is inoculated can multiply and form a clone to infect the animal, (iii) the probability of infection by any cell of the pathogen is independent of the number of cells ingested, and (iv) the magnitude of the immune response increases with dose, but eventually saturates to a maximum level. The probability of infection assessed by the DTH response is 7.5 x 10(-3)/c.f.u. of the inoculum (confidence interval 5.1 x 10(-5), 1.2 x 10(-2)). When five S. Enteritidis independently initiated the infection, the DTH response to the resulting clones of the salmonellae saturated to the maximum level. The probability of infection assessed by the neutrophil response is 3.4 x 10(-4)/c.f.u. (1.0 x 10(-4), 6.8 x 10(-4)). The response saturated when six S. Enteritidis independently initiated the infection. The probability of infection assessed by the analysis of spleens is 1.2 x 10(-3)/c.f.u. (4.1 x 10(-4), 2.6 x 10(-3)). We conclude that at low inocula, infections are initiated by very small numbers of bacteria. The magnitude of the immune responses is similar whether only a few or a larger number of bacteria initiated the infection.

Modelling inactivation of Escherichia coli by low pH: application to passage through the stomach of young and elderly people

AIM

To estimate the survival of enteropathogenic Escherichia coli after passage through the stomach of young and elderly people.

METHODS AND RESULTS

Using enterohaemorrhagic E. coli O157 and a non-pathogenic laboratory strain, inactivation in a pH range between 1.5 and 4.0 was experimentally quantified. Gastric pH and transport have previously been studied in human volunteers following consumption of a solid meal. Combining all these findings, time series of surviving bacteria were mathematically predicted and subsequently, the predictions were validated with in vitro experiments using a pH-controlled fermentor. On average, 20-80% of ingested E. coli are estimated to arrive in the small intestine without inactivation by low pH. The mean overall gastric passage was similar for young and elderly subjects.

CONCLUSIONS

The tested E. coli strains can survive the human stomach with a high probability.

SIGNIFICANCE AND IMPACT OF THE STUDY

Survival of E. coli under conditions of changing pH in the stomach may be predicted by batch experiments at constant pH. The effectiveness of the gastric acid barrier strongly depends on buffering effects of food.

Effect of accelerated natural lactic fermentation of infant food ingredients on some pathogenic microorganisms

Accelerated natural lactic fermentation in mixtures of water and ground sorghum, millet and pigeon pea was obtained by gradual selection of lactic acid bacteria, through inoculum recycling. Weaning food prepared from ingredients fermented this way, contained approx. 0.7% lactic and 0.05% acetic acids and had a pH of about 3.8. In porridges, a pH of less than or equal to 4.0 was required to cause death of Salmonella typhimurium and Staphylococcus aureus. Several intestinal pathogenic bacteria were inoculated into sour porridge. The most resistant Salmonella sp. died at a rate of 1.2 log cycle/h; the most resistant Shigella sp. at 0.9 log cycle/h; and the most resistant Escherichia coli strain at 0.6 log cycle/h. A yeast, Candida albicans, could grow well in the sour product, whereas a bacteriophage (MS-2) was inactivated at a rate of 0.1 log cycle/h. In the acid-sensitive bacterial cultures, no gradual adaptation to acid environments could be observed. The survival studies were carried out at 30 degrees C.

Production of "Asao toxin" by Aeromonas strains isolated from feces and drinking water

Cultures of Aeromonas species were tested for production of a toxin recently purified by Asao et al. (T. Asao, Y. Kinoshita, S. Kozaki, T. Uemura, and G. Sukaguchi, Infect. Immun. 46:122-127, 1984) and described as a hemolysin with enterotoxic and cytotoxic activity. The toxin was produced by only 63% of Aeromonas sobria strains and by 93% of Aeromonas hydrophila strains. Also, 54% of A. hydrophila strains produced another cytotoxic entity.