Enteric pathogens, intestinal permeability and nitric oxide production in acute gastroenteritis

Seropositivity and geographical distribution of Strongyloides stercoralis in Australia: A study of pathology laboratory data from 2012-2016

Background

There are no national prevalence studies of Strongyloides stercoralis infection in Australia, although it is known to be endemic in northern Australia and is reported in high risk groups such as immigrants and returned travellers. We aimed to determine the seropositivity (number positive per 100,000 of population and percent positive of those tested) and geographical distribution of S. stercoralis by using data from pathology laboratories.

Methodology

We contacted all seven Australian laboratories that undertake Strongyloides serological (ELISA antibody) testing to request de-identified data from 2012–2016 inclusive. Six responded. One provided positive data only. The number of people positive, number negative and number tested per 100,000 of population (Australian Bureau of Statistics data) were calculated including for each state/territory, each Australian Bureau of Statistics Statistical Area Level 3 (region), and each suburb/town/community/locality. The data was summarized and expressed as maps of Australia and Greater Capital Cities.

Principal findings

We obtained data for 81,777 people who underwent serological testing for Strongyloides infection, 631 of whom were from a laboratory that provided positive data only. Overall, 32 (95% CI: 31, 33) people per 100,000 of population were seropositive, ranging between 23/100,000 (95% CI: 19, 29) (Tasmania) and 489/100,000 population (95%CI: 462, 517) (Northern Territory). Positive cases were detected across all states and territories, with the highest (260-996/100,000 and 17–40% of those tested) in regions across northern Australia, north-east New South Wales and north-west South Australia. Some regions in Greater Capital Cities also had a high seropositivity (112-188/100,000 and 17–20% of those tested). Relatively more males than females tested positive. Relatively more adults than children tested positive. Children were under-represented in the data.

Conclusions/Significance

The study confirms that substantial numbers of S. stercoralis infections occur in Australia and provides data to inform public health planning.

Strongyloides stercoralis, a parasitic roundworm, is endemic in many countries world-wide. In Australia, groups at risk for strongyloidiasis include Aboriginal and/or Torres Strait Islander people, who acquired this parasite locally, and immigrants and returned travellers who acquired the infection outside Australia. We obtained deidentified results of ELISA IgG antibody tests for Strongyloides from diagnostic pathology laboratories during 2012 to 2016 and calculated the number of people who were positive at least once and the number who never had a positive result. We drew maps showing the number positive per 100,000 of population, the percent positive of those tested, and the number tested/100,000 for each region and the number positive in each suburb of residence according to the Australian Bureau of Statistics. The highest seropositivity (260-996/100,000 of population) was in Northern Australia, north-west South Australia and north-east New South Wales where many Aboriginal and Torres Strait Islander people live in remote communities. There were also some regions in Greater Capital Cities with a high number of people positive per 100,000 of population (112-188/100,000), likely reflecting higher populations of immigrants and returned travellers who were infected outside Australia.

The Interrelationships between Intestinal Permeability and Phlegm Syndrome and Therapeutic Potential of Some Medicinal Herbs

The gastrointestinal (GI) tract has an intriguing and critical role beyond digestion in both modern and complementary and alternative medicine (CAM), as demonstrated by its link with the immune system. In this review, we attempted to explore the interrelationships between increased GI permeability and phlegm, an important pathological factor in CAM, syndrome, and therapeutic herbs for two disorders. The leaky gut and phlegm syndromes look considerably similar with respect to related symptoms, diseases, and suitable herbal treatment agents, including phytochemicals even though limitations to compare exist. Phlegm may be spread throughout the body along with other pathogens via the disruption of the GI barrier to cause several diseases sharing some parts of symptoms, diseases, and mechanisms with leaky gut syndrome. Both syndromes are related to inflammation and gut microbiota compositions. Well-designed future research should be conducted to verify the interrelationships for evidence based integrative medicine to contribute to the promotion of public health. In addition, systems biology approaches should be adopted to explore the complex synergistic effects of herbal medicine and phytochemicals on conditions associated with phlegm and leaky gut syndromes.

Integrating testing for chronic strongyloidiasis within the Indigenous adult preventive health assessment system in endemic communities in the Northern Territory, Australia: An intervention study

Background

The life-threatening clinical manifestations of strongyloidiasis are preventable with early detection and effective treatment. The aim of this study was to assess if there was an increase to the number and proportion of persons tested for chronic strongyloidiasis, as a result of integrating Strongyloides stercoralis serology into the existing preventive health assessment system in four Aboriginal health services in endemic communities.

Methodology

A prospective, longitudinal, before-and-after intervention study was conducted in four Aboriginal health services in remote endemically infected communities in the Northern Territory, Australia, from July 2012 to December 2016. The electronic patient information and recall systems enabled the integration of Strongyloides stercoralis serology into the adult preventive health assessment. Strongyloides reports for each health service were extracted half-yearly to examine the number and proportion of persons tested for chronic strongyloidiasis during the study and to measure the effect of the intervention.

Principal findings

The number and proportion of persons tested increased significantly during the study. From a total resident population of 3650 Indigenous adults over 15 years of age, 1686 persons (47.4%) were tested. The percentage of adults who had at least one serology test increased in all four health services to between 41% (446/1086) and 81.9% (172/210). Of the 1686 persons tested, 680 positive cases of chronic strongyloidiasis (40.3%) were identified.

Conclusions/Significance

This population health systems intervention increased the number and proportion of persons tested for chronic strongyloidiasis in four health services in endemically infected communities. This intervention is relevant to other health services with high-risk populations.

Strongyloidiasis is a neglected tropical disease that is endemic in some Aboriginal communities in the Northern Territory. This study asks if the number and proportion of persons tested for chronic strongyloidiasis can be increased by incorporating a Strongyloides serology test into the existing routine Indigenous adult preventive health assessment system in remote endemic communities. This study demonstrated that integrating Strongyloides serology test within the Indigenous adult preventive health assessment system does increase the number and proportion of people tested in endemic communities. This intervention means that life-threatening clinical complications of strongyloidiasis can be prevented by early detection and treatment. Primary health care services have an important role in increased testing in this high-risk population. Primary health care clinicians incorporated chronic strongyloidiasis with other preventable chronic and infectious diseases. The sustainable population health systems-based approach successfully increased coverage by integrating testing for chronic strongyloidiasis into the adult preventive health assessment in health services in remote Indigenous Australian endemic communities, utilising the electronic health record system. The Strongyloides report developed to measure the change in clinical practice would be replicable in other health services with high risk populations.

Plasma citrulline, arginine, nitric oxide, and blood ammonia levels in neonatal calves with acute diarrhea

Background

Plasma citrulline (CIT) concentration is considered to be a reliable marker of functional enterocyte mass, primarily in humans. However, information about CIT levels along with related metabolites, arginine (ARG), nitric oxide (NO), and ammonia in neonatal calves are lacking.

Objectives

To compare plasma CIT, ARG, NO, and whole blood ammonia concentrations in neonatal calves with acute diarrhea with those in healthy calves and to assess their possible relationships with diarrhea‐related criteria.

Animals

Seventy neonatal calves (60 with acute diarrhea and 10 healthy).

Methods

Observational case‐control study. Diarrheic calves were classified into subgroups on the basis of etiology, severity of diarrhea, degree of dehydration, and systemic inflammatory response syndrome (SIRS) status. Plasma CIT and ARG concentrations were measured by liquid chromatography/tandem mass spectrometry.

Results

Plasma CIT (median [range]: 67.5 [61.9‐75.4] vs 30.1 [15.0‐56.1] μmol/L) and ARG (170.7 [148.5‐219.5] vs 106.1 [54.4‐190.7] μmol/L) were lower and plasma NO (4.42 [3.29‐5.58] vs 6.78 [5.29‐8.92] μM) and blood ammonia concentrations (28.7 [26.1‐36.9] vs 59.8 [34.6‐99.5] μmol/L) were higher in the neonatal calves with diarrhea (P < .001). Plasma CIT (β = −0.29, P = .02), ARG (β = −0.33, P = .01), NO (β = 0.55, P < .001), and blood ammonia (β = 0.63, P <.001) were affected by SIRS status. Except for ammonia (0.52), the effects sizes for severity of diarrhea and degree of dehydration were small (ηp2 ≤ 0.45) for CIT, ARG, and NO.

Conclusions and Clinical Importance

The changes in these variables might have diagnostic, prognostic, and therapeutic value in diarrheic neonatal calves.

Paediatric Strongyloidiasis in Central Australia

Few published studies are available describing the prevalence of paediatric strongyloidiasis in endemic areas within Australia. This literature review and exploratory clinical audit presents the first seroprevalence data for paediatric patients in Central Australia. A total of 16.1% (30/186) of paediatric inpatients tested for Strongyloides stercoralis in 2016 were seropositive (95% CI: 11.5% to 22.1%). Eosinophilia of unknown aetiology was the most common indication for testing (91.9%). Seropositive patients were significantly more likely to reside in communities outside of Alice Springs (p = 0.02). Seropositive patients were noted to have higher mean eosinophil counts with a mean difference of 0.86 × 10⁸/L (95% CI: 0.56 to 1.16, p < 0.0001), although the limited utility of eosinophilia as a surrogate marker of strongyloidiasis has been described previously. All seropositive patients were Indigenous. There was no significant difference in ages between groups. There was a male predominance in the seropositive group, although this was not significant (p = 0.12). Twelve patients had known human T-lymphotropic virus 1 (HTLV-1) status and all were seronegative. Further research describing the epidemiology of strongyloidiasis in Central Australia is required.

Application of PCR-Based Tools to Explore Strongyloides Infection in People in Parts of Northern Australia

Strongyloidiasis, which is caused by infection with the nematode Strongyloides stercoralis, is endemic to areas of northern Australia. Diagnosis in this region remains difficult due to the distances between endemic communities and diagnostic laboratories, leading to lengthy delays in stool processing for microscopy and culture. PCR represents a viable solution to this difficulty, having potential for high sensitivity detection of S. stercoralis, even in older, unpreserved faecal samples. We prospectively collected 695 faecal specimens that were submitted to The Townsville Hospital Microbiology Laboratory from the North Queensland region for routine parasitological examination, and subjected them to a Strongyloides sp. real-time (q)PCR. Results were confirmed with a novel nested conventional PCR assay targeting the 18S rRNA gene, followed by single-strand conformation polymorphism analysis (SSCP). Of the 695 specimens tested, S. stercoralis was detected in three specimens (0.4%) by classical parasitological methods (direct microscopy and formyl-ether acetate concentration), whereas 42 positives were detected by qPCR (6.0%). Conventional PCR confirmed the real-time PCR results in 24 of the samples (3.5%). Several apparent false-positive results occurred at higher cycle times (C_t) in the qPCR. Use of real-time PCR in these populations is promising for the enhanced detection of disease and to support eradication efforts.

Association of enteric parasitic infections with intestinal inflammation and permeability in asymptomatic infants of São Tomé Island

The cumulative effect of repeated asymptomatic enteric infections on intestinal barrier is not fully understood in infants. We aimed to evaluate the association between previous enteric parasitic infections and intestinal inflammation and permeability at 24-months of age, in asymptomatic infants of São Tomé Island. A subset of infants from a birth cohort, with intestinal parasite evaluations in at least four points of assessment, was eligible. Intestinal inflammatory response and permeability were assessed using fecal S100A12 and alpha-1-antitrypsin (A1AT), respectively. The cutoff <-1SD for weight-for-length and length-for-age was used to define wasting and stunting. Multivariable linear regression analysis explored if cumulative enteric parasitic infections explained variability of fecal biomarkers, after adjusting for potential confounders. Eighty infants were included. Giardia duodenalis and soil-transmitted helminths (STH) were the most frequent parasites. The median (interquartile range) levels were 2.87 μg/g (2.41-3.92) for S100A12 and 165.1 μg/g (66.0-275.6) for A1AT. Weak evidence of association was found between S100A12 levels and G. duodenalis (p = 0.080) and STH infections (p = 0.089), and between A1AT levels and parasitic infection of any etiology (p = 0.089), at 24-months of age. Significant associations between A1AT levels and wasting (p = 0.006) and stunting (p = 0.044) were found. Previous parasitic infections were not associated with fecal biomarkers at 24 months of age. To summarize, previous asymptomatic parasitic infections showed no association with intestinal barrier dysfunction. Notwithstanding, a tendency toward increased levels of the inflammatory biomarker was observed for current G. duodenalis and STH infections, and increased levels of the permeability biomarker were significantly associated with stunting and wasting.

Activation of COX-2/PGE2 Promotes Sapovirus Replication via the Inhibition of Nitric Oxide Production

Enteric caliciviruses in the genera Norovirus and Sapovirus are important pathogens that cause severe acute gastroenteritis in both humans and animals. Cyclooxygenases (COXs) and their final product, prostaglandin E₂ (PGE₂), are known to play important roles in the modulation of both the host response to infection and the replicative cycles of several viruses. However, the precise mechanism(s) by which the COX/PGE₂ pathway regulates sapovirus replication remains largely unknown. In this study, infection with porcine sapovirus (PSaV) strain Cowden, the only cultivable virus within the genus Sapovirus, markedly increased COX-2 mRNA and protein levels at 24 and 36 h postinfection (hpi), with only a transient increase in COX-1 levels seen at 24 hpi. The treatment of cells with pharmacological inhibitors, such as nonsteroidal anti-inflammatory drugs or small interfering RNAs (siRNAs) against COX-1 and COX-2, significantly reduced PGE₂ production, as well as PSaV replication. Expression of the viral proteins VPg and ProPol was associated with activation of the COX/PGE₂ pathway. We observed that pharmacological inhibition of COX-2 dramatically increased NO production, causing a reduction in PSaV replication that could be restored by inhibition of nitric oxide synthase via the inhibitor N-nitro-l-methyl-arginine ester. This study identified a pivotal role for the COX/PGE₂ pathway in the regulation of NO production during the sapovirus life cycle, providing new insights into the life cycle of this poorly characterized family of viruses. Our findings also reveal potential new targets for treatment of sapovirus infection.

IMPORTANCE

Sapoviruses are among the major etiological agents of acute gastroenteritis in both humans and animals, but little is known about sapovirus host factor requirements. Here, using only cultivable porcine sapovirus (PSaV) strain Cowden, we demonstrate that PSaV induced the vitalization of the cyclooxygenase (COX) and prostaglandin E₂ (PGE₂) pathway. Targeting of COX-1/2 using nonsteroidal anti-inflammatory drugs (NSAIDs) such as the COX-1/2 inhibitor indomethacin and the COX-2-specific inhibitors NS-398 and celecoxib or siRNAs targeting COXs, inhibited PSaV replication. Expression of the viral proteins VPg and ProPol was associated with activation of the COX/PGE₂ pathway. We further demonstrate that the production of PGE₂ provides a protective effect against the antiviral effector mechanism of nitric oxide. Our findings uncover a new mechanism by which PSaV manipulates the host cell to provide an environment suitable for efficient viral growth, which in turn can be a new target for treatment of sapovirus infection.

Enteric Parasites in Arctic Communities: Tip of the Iceberg?

Human enteric parasitoses, particularly from Cryptosporidium, were recently recognized as being highly prevalent in parts of the Arctic. This is important because cryptosporidiosis has been repeatedly associated with impaired growth and development and may synergize with other challenges faced by children in remote Arctic communities, such as overcrowding and food insecurity.

The Risk of Reported Cryptosporidiosis in Children Aged <5 Years in Australia is Highest in Very Remote Regions

The incidence of cryptosporidiosis is highest in children <5 years, yet little is known about disease patterns across urban and rural areas of Australia. In this study, we examine whether the risk of reported cryptosporidiosis in children <5 years varies across an urban-rural gradient, after controlling for season and gender. Using Australian data on reported cryptosporidiosis from 2001 to 2012, we spatially linked disease data to an index of geographic remoteness to examine the geographic variation in cryptosporidiosis risk using negative binomial regression. The Incidence Risk Ratio (IRR) of reported cryptosporidiosis was higher in inner regional (IRR 1.4 95% CI 1.2–1.7, p < 0.001), and outer regional areas (IRR 2.4 95% CI 2.2–2.9, p < 0.001), and in remote (IRR 5.2 95% CI 4.3–6.2, p < 0.001) and very remote (IRR 8.2 95% CI 6.9–9.8, p < 0.001) areas, compared to major cities. A linear test for trend showed a statistically significant trend with increasing remoteness. Remote communities need to be a priority for future targeted health promotion and disease prevention interventions to reduce cryptosporidiosis in children <5 years.

Prevalence and molecular characterization of Cryptosporidium spp. and Giardia duodenalis in diarrhoeic patients in the Qikiqtani Region, Nunavut, Canada

Background

Although the prevalences of infection with the protozoan parasites Cryptosporidium spp. and Giardia duodenalis in humans appear to be relatively high in the Canadian North, their transmission patterns are poorly understood.

Objective

To determine the detection rate and the molecular characteristics of Cryptosporidium spp. and Giardia duodenalis in diarrhoeic patients in the Qikiqtani (Baffin Island) Region of Nunavut, Canada, in order to better understand the burden of illness and the potential mechanisms of transmission.

Study design/methods

Diarrhoeal stool specimens (n=108) submitted to the Qikiqtani General Hospital for clinical testing were also tested for the presence of Cryptosporidium spp. and Giardia duodenalis using epifluorescence microscopy and polymerase chain reaction (PCR). DNA sequencing and restriction fragment length polymorphism (RFLP) analyses were performed on PCR-positive specimens to determine the species, genotypes and sub-genotypes of the parasites.

Results

Cryptosporidium was detected in 15.7% of the diarrhoeic patients, while Giardia was detected in 4.6%. DNA sequencing of a fragment of the small subunit rRNA gene indicated that all of the Cryptosporidium amplicons had a 100% homology to C. parvum, and a gp60 assay showed that all aligned with C. parvum sub-genotype IIa. Microsatellite analysis revealed 3 cases of sub-genotype IIaA15G2R1, 2 of IIaA15G1R and 1 case each of sub-genotypes IIaA16G1R1 and IIaA15R1. For Giardia, results based on the amplification of both the 16S rRNA gene and the gdh gene were generally in agreement, and both DNA sequencing and RFLP demonstrated the presence of the G. duodenalis Assemblage B genotype.

Conclusions

Both C. parvum and G. duodenalis Assemblage B were present in human diarrhoeal stool specimens from Nunavut, which was suggestive of zoonotic transmission, although human-to-human transmission cannot be ruled out. To fully understand the public health significance of the different Cryptosporidium and Giardia species and genotypes in diarrhoeic patients, it will be imperative to establish the extent of genetic diversity within these parasites through comprehensive studies of the molecular epidemiology of cryptosporidiosis and giardiasis in the Nunavut region.

Strongyloides stercoralis: systematic review of barriers to controlling strongyloidiasis for Australian indigenous communities

Background

Strongyloides stercoralis infects human hosts mainly through skin contact with contaminated soil. The result is strongyloidiasis, a parasitic disease, with a unique cycle of auto-infection causing a variety of symptoms and signs, with possible fatality from hyper-infection. Australian Indigenous community members, often living in rural and remote settings, are exposed to and infected with S. stercoralis. The aim of this review is to determine barriers to control of strongyloidiasis. The purpose is to contribute to the development of initiatives for prevention, early detection and effective treatment of strongyloidiasis.

Methodology/Principle Findings

Systematic search reviewing research published 2012 and earlier was conducted. Research articles discussing aspects of strongyloidiasis, context of infection and overall health in Indigenous Australians were reviewed. Based on the PRISMA statement, the systematic search of health databases, Academic Search Premier, Informit, Medline, PubMed, AMED, CINAHL, Health Source Nursing and Academic was conducted. Key search terms included strongyloidiasis, Indigenous, Australia, health, and community. 340 articles were retrieved with 16 original research articles published between 1969 and 2006 meeting criteria. Review found barriers to control defined across three key themes, (1) health status, (2) socioeconomic status, and (3) health care literacy and procedures.

Conclusions/Significance

This study identifies five points of intervention: (1) develop reporting protocols between health care system and communities; (2) test all Indigenous Australian patients, immunocompromised patients and those exposed to areas with S. stercoralis; (3) health professionals require detailed information on strongyloidiasis and potential for exposure to Indigenous Australian people; (4) to establish testing and treatment initiatives within communities; and (5) to measure and report prevalence rates specific to communities and to act with initiatives based on these results. By defining barriers to control of strongyloidiasis in Australian Indigenous people, improved outcomes of prevention, treatment of strongyloidiasis and increased health overall are attainable.

Strongyloides stercoralis, a nematode parasite, has a well-documented history of infecting human hosts in tropic and subtropic regions mainly through skin contact with inhabited soil. The result is strongyloidiasis, a human parasitic disease, with a unique cycle of auto-infection contributing to a variety of symptoms, of which, hyper-infection causing fatality may occur. In Australia, Indigenous community members often located in rural and remote settings, are exposed to and infected with strongyloides. Previous researchers report strongyloidiasis as a recurrent health issue for Indigenous Australians. This is a systematic review to determine the barriers to control for this pernicious pathogen. Barriers to control can be defined across three key themes: (1) health status, (2) socioeconomic status, and (3) health care literacy and procedure. By conceptualizing these barriers and addressing steps to control as outlined in this study, there is potential for improvement in prevention and treatment outcomes of strongyloidiasis and subsequently, overall health for Australian Indigenous people. This study contributes to furthering prevention and treatment of strongyloidiasis, increasing exposure to the issue of strongyloidiasis in Australian Indigenous people. It is the intent of this paper to express the need to have continued research and further health policy directed specifically to eradicate strongyloidiasis in Australian Indigenous communities.

Human strongyloidiasis: identifying knowledge gaps, with emphasis on environmental control

Strongyloides is a human parasitic nematode that is poorly understood outside a clinical context. This article identifies gaps within the literature, with particular emphasis on gaps that are hindering environmental control of Strongyloides. The prevalence and distribution of Strongyloides is unclear. An estimate of 100-370 million people infected worldwide has been proposed; however, inaccuracy of diagnosis, unreliability of prevalence mapping, and the fact that strongyloidiasis remains a neglected disease suggest that the higher figure of more than 300 million cases is likely to be a more accurate estimate. The complexity of Strongyloides life cycle means that laboratory cultures cannot be maintained outside of a host. This currently limits the range of laboratory-based research, which is vital to controlling Strongyloides through environmental alteration or treatment. Successful clinical treatment with antihelminthic drugs has meant that controlling Strongyloides through environmental control, rather than clinical intervention, has been largely overlooked. These control measures may encompass alteration of the soil environment through physical means, such as desiccation or removal of nutrients, or through chemical or biological agents. Repeated antihelminthic treatment of individuals with recurrent strongyloidiasis has not been observed to result in the selection of resistant strains; however, this has not been explicitly demonstrated, and relying on such assumptions in the long-term may prove to be shortsighted. It is ultimately naive to assume that continued administration of antihelminthics will be without any negative long-term effects. In Australia, strongyloidiasis primarily affects Indigenous communities, including communities from arid central Australia. This suggests that the range of Strongyloides extends beyond the reported tropical/subtropical boundary. Localized conditions that might result in this extended boundary include accumulation of moisture within housing because of malfunctioning health hardware inside and outside the house and the presence of dog fecal matter inside or outside housing areas.

Rotavirus infection increases intestinal motility but not permeability at the onset of diarrhea

The disease mechanisms associated with onset and secondary effects of rotavirus (RV) diarrhea remain to be determined and may not be identical. In this study, we investigated whether onset of RV diarrhea is associated with increased intestinal permeability and/or motility. To study the transit time, fluorescent fluorescein isothiocyanate (FITC)-dextran was given to RV-infected adult and infant mice. Intestinal motility was also studied with an opioid receptor agonist (loperamide) and a muscarinic receptor antagonist (atropine). To investigate whether RV increases permeability at the onset of diarrhea, fluorescent 4- and 10-kDa dextran doses were given to infected and noninfected mice, and fluorescence intensity was measured subsequently in serum. RV increased transit time in infant mice. Increased motility was detected at 24 h postinfection (h p.i.) and persisted up to 72 h p.i in pups. Both loperamide and atropine decreased intestinal motility and attenuated diarrhea. Analysis of passage of fluorescent dextran from the intestine into serum indicated unaffected intestinal permeability at the onset of diarrhea (24 to 48 h p.i.). We show that RV-induced diarrhea is associated with increased intestinal motility via an activation of the myenteric nerve plexus, which in turn stimulates muscarinic receptors on intestinal smooth muscles.

IMPORTANCE

We show that RV-infected mice have increased intestinal motility at the onset of diarrhea, and that this is not associated with increased intestinal permeability. These new observations will contribute to a better understanding of the mechanisms involved in RV diarrhea.

Intestinal permeability defects: is it time to treat?

An essential role of the intestinal epithelium is to separate luminal contents from the interstitium, a function primarily determined by the integrity of the epithelium and the tight junction that seals the paracellular space. Intestinal tight junctions are selectively permeable, and intestinal permeability can be increased physiologically in response to luminal nutrients or pathologically by mucosal immune cells and cytokines, the enteric nervous system, and pathogens. Compromised intestinal barrier function is associated with an array of clinical conditions, both intestinal and systemic. Although most available data are correlative, some studies support a model where cycles of increased intestinal permeability, intestinal immune activation, and subsequent immune-mediated barrier loss contribute to disease progression. This model is applicable to intestinal and systemic diseases. However, it has not been proven, and both mechanistic and therapeutic studies are ongoing. Nevertheless, the correlation between increased intestinal permeability and disease has caught the attention of the public, leading to a rise in popularity of the diagnosis of "leaky gut syndrome," which encompasses a range of systemic disorders. Proponents claim that barrier restoration will cure underlying disease, but this has not been demonstrated in clinical trials. Moreover, human and mouse studies show that intestinal barrier loss alone is insufficient to initiate disease. It is therefore uncertain whether increased permeability in these patients is a cause or effect of the underlying disorder. Although drug targets that may mediate barrier restoration have been proposed, none have been proven effective. As such, current treatments for barrier dysfunction should target the underlying disease.

Strongyloides stercoralis: Global Distribution and Risk Factors

BACKGROUND

The soil-transmitted threadworm, Strongyloides stercoralis, is one of the most neglected among the so-called neglected tropical diseases (NTDs). We reviewed studies of the last 20 years on S. stercoralis's global prevalence in general populations and risk groups.

METHODS/PRINCIPAL FINDINGS

A literature search was performed in PubMed for articles published between January 1989 and October 2011. Articles presenting information on infection prevalence were included. A Bayesian meta-analysis was carried out to obtain country-specific prevalence estimates and to compare disease odds ratios in different risk groups taking into account the sensitivities of the diagnostic methods applied. A total of 354 studies from 78 countries were included for the prevalence calculations, 194 (62.4%) were community-based studies, 121 (34.2%) were hospital-based studies and 39 (11.0%) were studies on refugees and immigrants. World maps with country data are provided. In numerous African, Asian and South-American resource-poor countries, information on S. stercoralis is lacking. The meta-analysis showed an association between HIV-infection/alcoholism and S. stercoralis infection (OR: 2.17 BCI: 1.18-4.01; OR: 6.69; BCI: 1.47-33.8), respectively.

CONCLUSIONS

Our findings show high infection prevalence rates in the general population in selected countries and geographical regions. S. stercoralis infection is prominent in several risk groups. Adequate information on the prevalence is still lacking from many countries. However, current information underscore that S. stercoralis must not be neglected. Further assessments in socio-economic and ecological settings are needed and integration into global helminth control is warranted.

Towards a human rotavirus disease model

While the clinical importance of human rotavirus (RV) disease is well recognized and potent vaccines have been developed, our understanding of how human RV causes diarrhoea, vomiting and death remains unresolved. The fact that oral rehydration corrects electrolyte and water loss, indicates that enterocytes in the small intestine have a functional sodium-glucose co-transporter. Moreover, RV infection delays gastric emptying and loperamide appears to attenuate RV diarrhoea, thereby suggesting activation of the enteric nervous system. Serotonin (5-HT) receptor antagonists attenuate vomiting in young children with gastroenteritis while zinc and enkephalinase inhibitors attenuate RV-induced diarrhoea. In this review we discuss clinical symptoms, pathology, histology and treatment practices for human RV infections and compile the data into a simplified disease model.

Pneumococcal carriage at age 2 months is associated with growth deficits at age 6 months among infants in South India

Nasopharyngeal colonization is the first step in the pathway to Streptococcus pneumoniae (Spn) infection, a leading cause of childhood morbidity and mortality. We investigated the effect of Spn colonization at ages 2 and 4 mo on growth at age 6 mo among 389 infants living in rural South India by using data from an Spn carriage study nested within a randomized, double-blind, placebo-controlled community trial designed to evaluate the impact of newborn vitamin A supplementation on Spn carriage in the first 6 mo of life. Primary outcomes were weight, length, and anthropometric indices of nutritional status. Growth data at age 6 mo were available for 84% (389 of 464) of infants in the Spn carriage study. Carriage at age 2 mo was associated with increased odds of stunting [OR: 3.07 (95% CI: 1.29, 7.36) P = 0.012] and lower weight [β: -266 g (95% CI: -527, -5) P = 0.045], length [β: -1.31 cm (95% CI: -2.32, -0.31) P = 0.010], and length-for-age Z scores [β: -0.59; (95% CI: -1.05, -0.13) P = 0.012] at age 6 mo. Spn carriage at age 4 mo did not affect growth. Carriage of invasive serotypes at age 2 mo was associated with decreases in mean weight [β: -289 g; (95% CI: -491, -106) P = 0.002] and length [β:-0.38 cm (95% CI: -1.49, -0.01) P = 0.047] at age 6 mo. Newborn vitamin A supplementation did not modify the association between Spn carriage and growth. Results suggest that pneumococcal carriage at age 2 mo is an independent risk factor for poor growth in young infants. Future studies need to clarify the role of Spn carriage on growth retardation in low-income countries.

Quantitative and qualitative evaluation of iNOS expression in turbot (Psetta maxima) infected with Enteromyxum scophthalmi

Enteromyxum scophthalmi is the causative agent of turbot enteromyxosis, an intestinal parasitisation that produces severe desquamative enteritis leading to a cachectic syndrome and eventually the death. It is well known the importance of the innate immune response against parasites in fish, with the release of antimicrobial substances such as reactive oxygen and nitrogen species, produced by the inducible nitric oxide synthase (iNOS). This enzyme is mainly found in phagocytes, but also in structural cells from the intestinal mucosa. The aim of this study was to characterize iNOS in intestine and lymphohaematopoietic organs (spleen and anterior kidney) of turbot by means of immunohistochemistry in order to assess the possible changes of this enzyme through the infection. The presence of the enzyme was evaluated in control and E. scophthalmi-infected turbot. The results showed immunoreactivity in the apical border of enterocytes and mild staining of goblet cells in both control and infected turbot although it was more evident and widespread in infected turbot compared to control. Moderate numbers of iNOS+ cells were present in the lamina propria-submucosa of fish which presented moderate and severe inflammatory infiltrates at this level. In spleen and kidney, iNOS+ cells were scattered through the parenchyma and, in severely infected fish, tended to be allocated near the vascular structures and melano-macrophage centres. The number of positive cells at the lymphohaematopoietic organs was significantly higher in infected turbot and increased as infection progressed. The increase in the expression of iNOS in the tissues of E. scophthalmi-infected turbot was more evident in individuals with severer lesions. The measurement of the levels of iNOS during turbot enteromyxosis reveals a possibly delayed response that would not able to eliminate the parasites but would exacerbate mucosal injury.

Efficacy of Lactobacillus GG in aboriginal children with acute diarrhoeal disease: a randomised clinical trial

OBJECTIVE

The effectiveness of probiotic therapy for acute rotavirus infectious diarrhoea in an indigenous setting with bacterial/parasitic diarrhoea is unclear. In the present study, we assessed the efficacy of probiotics in Australian Aboriginal children in the Northern Territory admitted to hospital with diarrhoeal disease.

PATIENTS AND METHODS

A randomised double-blind placebo-controlled study was conducted in Aboriginal children (ages 4 months-2 years), admitted to hospital with acute diarrhoeal disease (>3 loose stools per day). Children received either oral Lactobacillus GG (5 x 10(9) colony-forming units 3 times per day for 3 days; n = 33) or placebo (n = 31). Small intestinal functional capacity was assessed by the noninvasive 13C-sucrose breath test on days 1 and 4.

RESULTS

Both groups showed mean improvement in the sucrose breath test after 4 days; however, there was no difference (mean, 95% confidence interval) between probiotic (2.9 [cumulative percentage of dose recovered at 90 minutes]; 1.7-4.2) and placebo (3.7; 2.3-5.2) groups. Probiotics did not change the duration of diarrhoea, total diarrhoea stools, or diarrhoea score compared with placebo. There was a significant (P < 0.05) difference in diarrhoea frequency on day 2 between probiotics (3.3 [loose stools]; 2.5-4.3) and placebo (4.7; 3.8-5.7) groups.

CONCLUSIONS

Lactobacillus GG did not appear to enhance short-term recovery following acute diarrhoeal illness in this setting.

Acute and persistent diarrhea

Socially disadvantaged Indigenous infants and children living in western industrialized countries experience high rates of infectious diarrhea, no more so than Aboriginal children from remote and rural regions of Northern Australia. Diarrheal disease, poor nutrition, and intestinal enteropathy reflect household crowding, inadequate water and poor sanitation and hygiene. Acute episodes of watery diarrhea are often best managed by oral glucose-electrolyte solutions with continuation of breastfeeding and early reintroduction of feeding. Selective use of lactose-free milk formula, short-term zinc supplementation and antibiotics may be necessary for ill children with poor nutrition, persistent symptoms, or dysentery. Education, high standards of environmental hygiene, breastfeeding, and immunization with newly licensed rotavirus vaccines are all needed to reduce the unacceptably high burden of diarrheal disease encountered in young children from Indigenous communities.

Nitric oxide production in acute gastroenteritis in Indian children

This study compared nitric oxide (NO) levels in 110 children with, and 110 children without, infectious gastroenteritis. Post-infection intestinal function was assessed in a subset. At least one pathogen was identified in 47.2% of cases. The most common diarrhoeal pathogens were rotavirus (22.7%) and norovirus genogroup II (11.8%). The levels of NO measured by median urinary nitrite:creatinine ratio were significantly higher in children with diarrhoea [23.6; interquartile range (IQR) 12.3-46.7] than without diarrhoea (7.8; IQR 4.1-13.2), P<0.001. The ratio was not significantly different between diarrhoeal cases with and without pathogens (P=0.148). Six of twelve children tested had intestinal dysfunction.

Characterisation of atypical enteropathogenic E. coli strains of clinical origin

BACKGROUND

Enteropathogenic E. coli (EPEC) is a prominent cause of diarrhoea, and is characterised in part by its carriage of a pathogenicity island: the locus for enterocyte effacement (LEE). EPEC is divided into two subtypes according to the presence of bundle-forming pili (BFP), a fimbrial adhesin that is a virulence determinant of typical EPEC (tEPEC), but is absent from atypical EPEC (aEPEC). Because aEPEC lack BFP, their virulence has been questioned, as they may represent LEE-positive Shiga toxin-producing E. coli (STEC) that have lost the toxin-encoding prophage, or tEPEC that have lost the genes for BFP. To determine if aEPEC isolated from humans in Australia or New Zealand fall into either of these categories, we undertook phylogenetic analysis of 75 aEPEC strains, and compared them with reference strains of EPEC and STEC. We also used PCR and DNA hybridisation to determine if aEPEC carry virulence determinants that could compensate for their lack of BFP.

RESULTS

The results showed that aEPEC are highly heterogeneous. Multilocus sequence typing revealed that 61 of 75 aEPEC strains did not belong to known tEPEC or STEC clades, and of those that did, none expressed an O:H serotype that is frequent in tEPEC or STEC strains associated with disease. PCR for each of 18 known virulence-associated determinants of E. coli was positive in less than 15% of strains, apart from NleB which was detected in 30%. Type I fimbriae were expressed by all aEPEC strains, and 12 strains hybridised with DNA probes prepared from either bfpA or bfpB despite being negative in the PCR for bfpA.

CONCLUSION

Our findings indicate that clinical isolates of aEPEC obtained from patients in Australia or New Zealand are not derived from tEPEC or STEC, and suggest that functional equivalents of BFP and possibly type I fimbriae may contribute to the virulence of some aEPEC strains.

Release of metabolic enzymes by Giardia in response to interaction with intestinal epithelial cells

Giardia lamblia, an important cause of diarrheal disease, resides in the small intestinal lumen in close apposition to epithelial cells. Since the disease mechanisms underlying giardiasis are poorly understood, elucidating the specific interactions of the parasite with the host epithelium is likely to provide clues to understanding the pathogenesis. Here we tested the hypothesis that contact of Giardia lamblia with intestinal epithelial cells might lead to release of specific proteins. Using established co-culture models, intestinal ligated loops and a proteomics approach, we identified three G. lamblia proteins (arginine deiminase, ornithine carbamoyl transferase and enolase), previously recognized as immunodominant antigens during acute giardiasis. Release was stimulated by cell-cell interactions, since only small amounts of arginine deiminase and enolase were detected in the medium after culturing of G. lamblia alone. The secreted G. lamblia proteins were localized to the cytoplasm and the inside of the plasma membrane of trophozoites. Furthermore, in vitro studies with recombinant arginine deiminase showed that the secreted Giardia proteins can disable host innate immune factors such as nitric oxide production. These results indicate that contact of Giardia with epithelial cells triggers metabolic enzyme release, which might facilitate effective colonization of the human small intestine.

Oral delivery of L-arginine stimulates prostaglandin-dependent secretory diarrhea in Cryptosporidium parvum-infected neonatal piglets

OBJECTIVES

To determine if oral supplementation with L-arginine could augment nitric oxide (NO) synthesis and promote epithelial defense in neonatal piglets infected with Cryptosporidium parvum.

MATERIALS AND METHODS

Neonatal piglets were fed a liquid milk replacer and on day 3 of age infected or not with 10(8) C. parvum oocysts and the milk replacer supplemented with L-arginine or L-alanine. Milk consumption, body weight, fecal consistency, and oocyst excretion were recorded daily. On day 3 postinfection, piglets were euthanized and serum concentration of NO metabolites and histological severity of villous atrophy and epithelial infection were quantified. Sheets of ileal mucosa were mounted in Ussing chambers for measurement of barrier function (transepithelial resistance and permeability) and short-circuit current (an indirect measurement of Cl secretion in this tissue).

RESULTS

C. parvum-infected piglets had large numbers of epithelial parasites, villous atrophy, decreased barrier function, severe watery diarrhea, and failure to gain weight. L-Arginine promoted synthesis of NO by infected piglets, which was unaccompanied by improvement in severity of infection but rather promoted epithelial chloride secretion and diarrhea. Epithelial secretion by infected mucosa from L-arginine-supplemented piglets was fully inhibited by the cyclooxygenase inhibitor indomethacin, indicating that prostaglandin synthesis was responsible for this effect.

CONCLUSIONS

Results of these studies demonstrate that provision of additional NO substrate in the form of L-arginine incites prostaglandin-dependent secretory diarrhea and does not promote epithelial defense or barrier function of C. parvum-infected neonatal ileum.

Critical appraisal of the management of severe malnutrition: 3. Complications

The high case-fatality of severe malnutrition is due to infections, dehydration, electrolyte disturbances and heart failure. We focus on the evidence about managing these complications of severe malnutrition. Signs of circulatory collapse in severely malnourished children should be treated with intravenous or bone marrow infusion of Ringer's lactate with additional dextrose and potassium at a rate 20-40 mL/kg fast with close monitoring of vital signs. Recommendations for slow or restricted fluids in the face of shock are unsafe, and hypotonic or maintenance solutions must be avoided to prevent hyponatraemia. However, the evidence that severely malnourished children do not tolerate excessive fluid administration is good, so caution must be exercised with regards to fluids in the initial phase of treatment. There is also good evidence that wide spectrum antibiotics need to be given empirically for severe malnutrition to prevent the otherwise unavoidable early mortality. There is a need for improved protocols for tuberculosis diagnosis, HIV management and treatment of infants under 6 months with severe malnutrition. The contribution of environmental enteropathy to poor growth and nutrition during the weaning period means that there should be more priority on improving environmental health, particularly better hygiene and less overcrowding. A T-cell mediated enteropathy contributes to growth failure and malnutrition, and it is related to environmental contamination of enteric organisms in the weaning period rather than allergic responses.

Burden of severe rotavirus disease in Australia

AIM

To analyse the epidemiology of coded rotavirus hospitalisations in Australia from 1993 to 2002, with a view to understanding the pre-vaccination burden of severe disease in Australia. This study also seeks to determine the burden of rotavirus-related mortality.

METHODS

Hospitalisation data from the Australian Institute of Health and Welfare for the period 1993-2002 were analysed. Rotavirus-related mortality data from the National Mortality Database were also analysed for the period 1990-2002.

RESULTS

There were an average of 4260 patients hospitalised for rotavirus each year. The majority of rotavirus hospitalisations occurred in those under the age of 5 years, with the highest rate being in those aged 6-12 months (618.4 per 100,000). The Northern Territory was the most distinct region, with exceptionally high rates of admission (148.9 per 100,000 total population), younger age of admission and longer lengths of stay. Mapping of rotavirus hospitalisation in Australia showed well-defined areas of high hospitalisation rates. Thirteen rotavirus-related deaths occurred during 1990-2002.

CONCLUSION

Rotavirus infection causes considerable morbidity and mortality in Australia. A vaccination programme would need to be completed by 6 months of age to have maximal impact.

Enteroaggregative Escherichia coli Is a Cause of Acute Diarrheal Illness: A Meta-Analysis

BACKGROUND

Conflicting studies exist regarding the role of enteroaggregative Escherichia coli (EAEC) as a cause of acute diarrheal illness. The objective of this meta-analysis was to determine whether identification of EAEC in stool samples is associated with acute diarrheal illness among different subpopulations, by geographic area.

METHODS

A comprehensive search of electronic bibliographic databases (Medline and PubMed) from August 1985 to January 2006, as well as a search of conference proceedings, references of articles, and contacts with investigators of EAEC, yielded 354 studies.

RESULTS

Forty-one studies (12%) that met the selection criteria (i.e., that examined the association between acute diarrheal illness and the excretion of EAEC among different subpopulations) were included. In this meta-analysis, presence of EAEC identified with the HEp-2 cell adherence assay was found to be significantly associated with acute diarrheal illness among children residing in developing regions (odds ratio [OR], 1.58; 95% confidence interval [CI], 1.36-1.83) and industrialized regions (OR, 1.23; 95% CI, 1.03-1.48), adults with human immunodeficiency virus infection residing in developing regions (OR, 6.43; 95% CI, 2.91-14.16), adults residing in developing regions (OR, 7.15; 95% CI, 1.96-26.04), and international travelers to developing regions (OR, 6.72; 95% CI, 2.62-17.20). A limited number of studies were available that examined the role of EAEC identified by its virulence genes by a DNA probe.

CONCLUSIONS

On the basis of this meta-analysis, we conclude that EAEC is a cause of acute diarrheal illness among many different subpopulations in both developing and industrialized regions, that EAEC strains are very heterogeneous and that additional studies that examine the role of EAEC in acute diarrheal illness are needed.

Role of nitric oxide during rotavirus infection

The pathophysiological mechanisms behind rotavirus-induced diarrhoea still remain incomplete. Current views suggest that the non-structural protein 4 (NSP4) of rotavirus and the enteric nervous system (ENS) participate in water secretion and diarrhoea. In the present work the role of nitric oxide (NO) in rotavirus infection and disease has been studied in vitro, mice and humans. Incubation of human intestinal epithelial cells (HT-29) with purified NSP4 but not with infectious virus produced NO2/NO3 accumulation in the incubation media. The NSP4-induced release of NO metabolites occurred within the first minutes after the addition of the toxin. Mice infected with murine rotavirus (strain EDIM) accumulated NO2/NO3 in the urine at the onset for diarrhoea. Following rotavirus infection, inducible nitric oxide synthetase (iNOS) mRNA was upregulated in ileum, but not in duodenum or jejunum of newborn pups within 5 days post-infection. A prospective clinical study including 46 children with acute rotavirus infection and age-matched controls concluded that rotavirus infection stimulates NO production during the course of the disease (P < 0.001). These observations identify NO as an important mediator of host responses during rotavirus infection.

Atypical enteropathogenic Escherichia coli infection and prolonged diarrhea in children

Some clinical isolates of enteropathogenic Escherichia coli (EPEC) lack bundle-forming pili and are termed atypical EPEC. The aim of this study was to determine if atypical EPEC are pathogens by comparing the clinical features of patients infected with atypical EPEC with those of children infected with other causative agents of diarrhea. Fecal samples obtained from children attending the Royal Children's Hospital in Melbourne for investigation of diarrhea were examined for adenovirus, rotavirus, Campylobacter spp., Salmonella spp., protozoa, and pathogenic E. coli. Clinical data were obtained by using a standardized pro forma and analyzed separately. Patients infected with atypical EPEC experienced mild, nondehydrating, and noninflammatory diarrhea that was not particularly associated with fever, vomiting, or abdominal pain. However, the duration of diarrhea in patients infected with atypical EPEC was significantly longer than that caused by the other species or where no pathogens were identified. Infection with atypical EPEC is associated with prolonged diarrhea.

Changes in Tissue Nitrite Concentration in the Crop of the Turkey Poult in Response to Salmonella Typhimurium Challenge

The present study examines whether Salmonella typhimurium colonization of the crop of young turkeys influences nitrite concentration in the component tissues of the crop. Nitric oxide (NO) is the principal compound in biological samples that is converted into nitrites and NO is known to be a component of the early host response to infection. Challenge with S. typhimurium increased the concentration of nitrite in the crop wall of 3-wk-old turkey poults. The magnitude of the response was reduced at 8 h and absent at 48 h after challenge. As would be expected, S. typhimurium concentrations in the crop were markedly increased following challenge, and were nondetectable in control poults.

NF-kappaB-mediated expression of iNOS promotes epithelial defense against infection by Cryptosporidium parvum in neonatal piglets

Cryptosporidium sp. parasitizes intestinal epithelium, resulting in enterocyte loss, villous atrophy, and malabsorptive diarrhea. We have shown that mucosal expression of inducible nitric oxide (NO) synthase (iNOS) is increased in infected piglets and that inhibition of iNOS in vitro has no short-term effect on barrier function. NO exerts inhibitory effects on a variety of pathogens; nevertheless, the specific sites of iNOS expression, pathways of iNOS induction, and mechanism of NO action in cryptosporidiosis remain unclear. Using an in vivo model of Cryptosporidium parvum infection, we have examined the location, mechanism of induction, specificity, and consequence of iNOS expression in neonatal piglets. In acute C. parvum infection, iNOS expression predominated in the villous epithelium, was NF-kappaB dependent, and was not restricted to infected enterocytes. Ongoing treatment of infected piglets with a selective iNOS inhibitor resulted in significant increases in villous epithelial parasitism and oocyst excretion but was not detrimental to maintenance of mucosal barrier function. Intensified parasitism could not be attributed to attenuated fluid loss or changes in epithelial proliferation or replacement rate, inasmuch as iNOS inhibition did not alter severity of diarrhea, piglet hydration, Cl- secretion, or kinetics of bromodeoxyuridine-labeled enterocytes. These findings suggest that induction of iNOS represents a nonspecific response of the epithelium that mediates enterocyte defense against C. parvum infection. iNOS did not contribute to the pathogenic sequelae of C. parvum infection.

Strongyloidiasis: A review of the evidence for Australian practitioners

OBJECTIVE

To summarise the available evidence concerning the prevalence, clinical manifestations, diagnosis and management of strongyloidiasis in Northern Australia.

METHODS

We searched Medline, Clinical Evidence and the Cochrane Library using MeSH terms and text words 'strongyloides OR strongyloidiasis'. For Australian studies we included text words '(parasite* OR parasitic OR helminth*) AND Australia*'. We examined references contained in retrieved studies or identified from direct contact with researchers. Studies consistent with our objective that described their methods were eligible for inclusion.

RESULTS

The prevalence in some tropical Aboriginal communities is high. Infection can be asymptomatic, cause a range of clinical syndromes or death. It may become chronic. Infected patients are at risk of developing severe disseminated disease particularly with immune compromise. There is little information about the relative frequency of different clinical outcomes. Available diagnostic tools are imperfect. Stool examination has a low sensitivity. Serology may have a low specificity in high prevalence populations and has not been evaluated in Aboriginal populations. Antihelmintic drugs are relatively safe and effective. Community programs based on treatment of stool-positive cases have been associated with a reduced prevalence of strongyloidiasis. We found no studies examining alternative public health interventions.

CONCLUSION

There is a high prevalence in many Aboriginal communities. Strongyloides infection should be excluded prior to commencing immunosuppressive therapies in patients from endemic areas. Further studies examining the public health impact of strongyloidiasis, the role of the enzyme-linked immuno-sorbent assay serological test and population-based approaches to management of the disease in endemically infected Australian populations are needed.

Escherichia coli and community-acquired gastroenteritis, Melbourne, Australia

As part of a study to determine the effects of water filtration on the incidence of community-acquired gastroenteritis in Melbourne, Australia, we examined fecal samples from patients with gastroenteritis and asymptomatic persons for diarrheagenic strains of Escherichia coli. Atypical strains of enteropathogenic E. coli (EPEC) were the most frequently identified pathogens of all bacterial, viral, and parasitic agents in patients with gastroenteritis. Moreover, atypical EPEC were more common in patients with gastroenteritis (89 [12.8%] of 696) than in asymptomatic persons (11 [2.3%] of 489, p < 0.0001). Twenty-two random isolates of atypical EPEC that were characterized further showed marked heterogeneity in terms of serotype, genetic subtype, and carriage of virulence-associated determinants. Apart from the surface protein, intimin, no virulence determinant or phenotype was uniformly present in atypical EPEC strains. This study shows that atypical EPEC are an important cause of gastroenteritis in Melbourne.

Rectal nitric oxide gas and stool cytokine levels during the course of infectious gastroenteritis

Nitric oxide (NO) is known to be an important inflammatory mediator with a potential role in gastrointestinal diseases. We prospectively studied the luminal NO levels in 51 patients with infectious gastroenteritis, 35 patients with nonenteric bacterial infections, and 11 healthy control subjects. The levels of proinflammatory cytokines were simultaneously measured in the stools of patients with gastroenteritis. Rectal gas was sampled with balloon catheters made of silicone and was analyzed for NO levels by chemiluminescence. The median rectal NO level was 2,450 ppb in the acute phase of gastroenteritis and gradually decreased to 225 ppb after 3 to 8 weeks, whereas the median NO values were 150 ppb in patients with nonenteric bacterial infections and 100 ppb in healthy control subjects. Patients with Salmonella, Shigella, and Campylobacter infections generally had more severe symptoms and a higher median NO level (17,250 ppb) than patients with Clostridium difficile-associated diarrhea (median NO value, 275 ppb). Interleukin-1 beta levels were elevated in 82% of the patients at disease onset and decreased during the convalescent phase. In contrast, gamma interferon was detected in only 16% of the patients and was predominantly collected in stool samples collected during the subacute and convalescent stages. Our data point to the possibility of using this easy, minimally invasive method for luminal NO measurement as a diagnostic tool, among others, to evaluate the degree of intestinal inflammation in patients with infectious gastroenteritis.

Nitric oxide synthase stimulates prostaglandin synthesis and barrier function in C. parvum-infected porcine ileum

Cell culture models implicate increased nitric oxide (NO) synthesis as a cause of mucosal hyperpermeability in intestinal epithelial infection. NO may also mediate a multitude of subepithelial events, including activation of cyclooxygenases. We examined whether NO promotes barrier function via prostaglandin synthesis using Cryptosporidium parvum-infected ileal epithelium in residence with an intact submucosa. Expression of NO synthase (NOS) isoforms was examined by real-time RT-PCR of ileal mucosa from control and C. parvum-infected piglets. The isoforms mediating and mechanism of NO action on barrier function were assessed by measuring transepithelial resistance (TER) and eicosanoid synthesis by ileal mucosa mounted in Ussing chambers in the presence of selective and nonselective NOS inhibitors and after rescue with exogenous prostaglandins. C. parvum infection results in induction of mucosal inducible NOS (iNOS), increased synthesis of NO and PGE2, and increased mucosal permeability. Nonselective inhibition of NOS (NG-nitro-L-arginine methyl ester) inhibited prostaglandin synthesis, resulting in further increases in paracellular permeability. Baseline permeability was restored in the absence of NO by exogenous PGE2. Selective inhibition of iNOS [L-N6-(1-iminoethyl)-L-lysine] accounted for approximately 50% of NOS-dependent PGE2 synthesis and TER. Using an entire intestinal mucosa, we have demonstrated for the first time that NO serves as a proximal mediator of PGE2 synthesis and barrier function in C. parvum infection. Expression of iNOS by infected mucosa was without detriment to overall barrier function and may serve to promote clearance of infected enterocytes.

Enteroaggregative Escherichia coli: an emerging enteric pathogen

Enteroaggregative Escherichia coli (EAEC) represents an emerging pathogen that causes enteric and food-borne infectious diseases. Subgroups in many populations throughout the world are susceptible to EAEC infection. EAEC pathogenesis involves adherence to the intestinal mucosa; increased production and deposition of a mucus biofilm; and mucosal toxicity due to inflammation and cytokine release. Due to the heterogeneity of EAEC strains and differing host immune responses, not all EAEC infections are symptomatic. Recent data suggest that individuals with a homozygous genotype -251 AA single nucleotide polymorphism (SNP), in the IL-8 promoter region, are more susceptible to EAEC diarrhea. The HEp-2 cell adherent assay allows identification of EAEC's characteristic aggregative or "stacked brick" adherence pattern. Antimicrobial treatment of individuals who develop EAEC diarrhea should be individually based. Ciprofloxacin and rifaximin, compared to placebo, have been shown to significantly shorten the course of diarrhea in patients who developed EAEC infection. The objective of this review is to increase awareness of this important emerging pathogen and to discuss the epidemiology, pathogenesis, and host-pathogen factors associated with EAEC infection.

Soluble transferrin receptor in Aboriginal children with a high prevalence of iron deficiency and infection

OBJECTIVES

Aboriginal children in tropical Australia have a high prevalence of both iron deficiency and acute infections, making it difficult to differentiate their relative contributions to anaemia. The aims of this study were to compare soluble transferrin receptor with ferritin in iron deficiency anaemia (IDA), and to examine how best to distinguish the effect of iron deficiency from infection on anaemia.

METHODS

We conducted a prospective study of 228 admissions to Royal Darwin Hospital in children from 6 to 60 months of age. Transferrin receptor concentrations were measured by a particle-enhanced immunoturbidimetric assay and ferritin by a microparticle enzyme immunoassay.

RESULTS

On multiple regression, the best explanatory variables for haemoglobin differences (r2=33.7%, P<0.001) were mean corpuscular volume (MCV), red cell distribution width (RDW) and C-reactive protein (CRP); whereas transferrin receptor and ferritin were not significant (P>0.4). Using > or =2 abnormal indices (MCV, RDW, blood film)+haemoglobin <110 g/l as the reference standard for IDA, transferrin receptor produced a higher area under the curve on receiver operating characteristic curve analysis than ferritin (0.79 vs. 0.64, P<0.001) or the transferrin receptor-ferritin index (0.77). On logistic regression, the effect of acute infection (CRP) on haemoglobin was significant (P<0.001) at cut-offs of 105 and 110 g/l, but not at 100 g/l when only iron deficiency indicators (MCV, RDW, blood film) were significant.

CONCLUSIONS

Transferrin receptor does not significantly improve the diagnosis of anaemia (iron deficiency vs. infection) over full blood count and CRP, but in settings with a high burden of infectious diseases and iron deficiency, it is a more reliable adjunctive measure of iron status than ferritin.

Unique pattern of urinary tract calculi in Australian Aboriginal children

Young Aboriginal children in remote regions of tropical and desert Australia are at risk of developing urate stones in their upper urinary tract from an early age. These radiolucent calculi were only recognized with the availability of ultrasound diagnosis and are not associated with anatomic anomalies or abnormal uric acid production/metabolism. Although these stones appear to resolve spontaneously after the weaning period, some result in ureteric obstruction and infection which may lead to renal damage. This pattern of urolithiasis differs from the usual global urolithiasis pattern of either endemic bladder stones in young children in developing countries or predominantly calcium-based stones in upper tracts of older children and adults in affluent industrialized countries, where upper tract urate stones account for only a minority of childhood urinary tract stones. Risk factors for urate stones are low urine output and acidic urine. An association between urolithiasis and carbohydrate intolerance leading to chronic acidosis has been suggested for Aboriginal children, but existing limited evidence does not support this as a major aetiological factor. Although further studies on the epidemiology, natural history and management of these urate stones are needed, we believe the focus should be on improving the known social and environmental risk factors of remote Aboriginal children during the weaning period which contribute to the unacceptably high prevalence of failure to thrive, diarrhoeal disease, environmental enteropathy, iron deficiency and urolithiasis.

Increased nitric oxide production in acute diarrhoea is associated with abnormal gut permeability, hypokalaemia and malnutrition in tropical Australian aboriginal children

Australian Aboriginal children hospitalized with diarrhoeal disease have severe manifestations with acidosis, hypokalaemia, osmotic diarrhoea and abnormal small bowel permeability. Nitric oxide (NO) production is increased in diarrhoeal disease, but its relationship to mucosal function and diarrhoeal complications is not known. We examined the relationship between NO production and complications of acute diarrhoea in Aboriginal and non-Aboriginal children between February 1998 and February 2000. We enrolled 318 children admitted to Royal Darwin Hospital into one of three groups: acute diarrhoea, non-diarrhoeal controls with no inflammatory illness, and non-diarrhoeal controls with inflammatory illness. Nitric oxide production was measured by urine nitrate-creatinine (NOx/Cr) excretion on a low nitrate diet. Small bowel intestinal permeability was measured by the lactulose-rhamnose (L/R) ratio on a timed blood specimen. The NOx/Cr ratios were markedly elevated in Aboriginal diarrhoeal cases (geometric mean [GM] = 1.23, 95% confidence interval [95% CI] 1.07-1.44), lowest in non-Aboriginal non-inflammatory controls (GM = 0.13, 95% CI 0.10-0.16) and intermediate in all other groups (GM = 0.35, 95% CI 0.28-0.43). Convalescent levels (day 5) in the Aboriginal diarrhoeal group (GM = 1.02, 95% CI 0.82-1.28) were slower to fall than L/R ratios. Multivariate analysis in the diarrhoeal group indicated that high NO production was associated with abnormal permeability, hypokalaemia and malnutrition, but not with the severity of diarrhoea, acidosis or osmotic diarrhoea. We concluded that increased NO production may contribute to impaired mucosal barrier function and hypokalaemia in acute gastroenteritis, which may be the cost of the known gut-protective and antimicrobial effects mediated by NO in acute intestinal inflammation.