A Pediatric Cluster of Shigella dysenteriae Serotype 1 Diarrhea with Hemolytic Uremic Syndrome in 2 Families from France

The Role of the Complement System in the Pathogenesis of Infectious Forms of Hemolytic Uremic Syndrome

Hemolytic uremic syndrome (HUS) is an acute disease and the most common cause of childhood acute renal failure. HUS is characterized by a triad of symptoms: microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. In most of the cases, HUS occurs as a result of infection caused by Shiga toxin-producing microbes: hemorrhagic Escherichia coli and Shigella dysenteriae type 1. They account for up to 90% of all cases of HUS. The remaining 10% of cases grouped under the general term atypical HUS represent a heterogeneous group of diseases with similar clinical signs. Emerging evidence suggests that in addition to E. coli and S. dysenteriae type 1, a variety of bacterial and viral infections can cause the development of HUS. In particular, infectious diseases act as the main cause of aHUS recurrence. The pathogenesis of most cases of atypical HUS is based on congenital or acquired defects of complement system. This review presents summarized data from recent studies, suggesting that complement dysregulation is a key pathogenetic factor in various types of infection-induced HUS. Separate links in the complement system are considered, the damage of which during bacterial and viral infections can lead to complement hyperactivation following by microvascular endothelial injury and development of acute renal failure.

Haemolytic uraemic syndrome in children England, Wales, Northern Ireland, and Ireland: A prospective cohort study

Haemolytic uraemic syndrome (HUS) caused by infection with Shiga toxin-producing Escherichia coli (STEC) is a relatively rare but potentially fatal multisystem syndrome clinically characterised by acute kidney injury. This study aimed to provide robust estimates of paediatric HUS incidence in England, Wales, Northern Ireland, and the Republic of Ireland by using data linkage and case reconciliation with existing surveillance systems, and to describe the characteristics of the condition. Between 2011 and 2014, 288 HUS patients were included in the study, of which 256 (89.5%) were diagnosed as typical HUS. The crude incidence of paediatric typical HUS was 0.78 per 100,000 person-years, although this varied by country, age, gender, and ethnicity. The majority of typical HUS cases were 1 to 4 years old (53.7%) and female (54.0%). Clinical symptoms included diarrhoea (96.5%) and/or bloody diarrhoea (71.9%), abdominal pain (68.4%), and fever (41.4%). Where STEC was isolated (59.3%), 92.8% of strains were STEC O157 and 7.2% were STEC O26. Comparison of the HUS case ascertainment to existing STEC surveillance data indicated an additional 166 HUS cases were captured during this study, highlighting the limitations of the current surveillance system for STEC for monitoring the clinical burden of STEC and capturing HUS cases.

An attenuated Shigella mutant lacking the RNA-binding protein Hfq provides cross-protection against Shigella strains of broad serotype

Few live attenuated vaccines protect against multiple serotypes of bacterial pathogen because host serotype-specific immune responses are limited to the serotype present in the vaccine strain. Here, immunization with a mutant of Shigella flexneri 2a protected guinea pigs against subsequent infection by S. dysenteriae type 1 and S. sonnei strains. This deletion mutant lacked the RNA-binding protein Hfq leading to increased expression of the type III secretion system via loss of regulation, resulting in attenuation of cell viability through repression of stress response sigma factors. Such increased antigen production and simultaneous attenuation were expected to elicit protective immunity against Shigella strains of heterologous serotypes. Thus, the vaccine potential of this mutant was tested in two guinea pig models of shigellosis. Animals vaccinated in the left eye showed fewer symptoms upon subsequent challenge via the right eye, and even survived subsequent intestinal challenge. In addition, oral vaccination effectively induced production of immunoglobulins without severe side effects, again protecting all animals against subsequent intestinal challenge with S. dysenteriae type 1 or S. sonnei strains. Antibodies against common virulence proteins and the O-antigen of S. flexneri 2a were detected by immunofluorescence microscopy. Reaction of antibodies with various strains, including enteroinvasive Escherichia coli, suggested that common virulence proteins induced protective immunity against a range of serotypes. Therefore, vaccination is expected to cover not only the most prevalent serotypes of S. sonnei and S. flexneri 2a, but also various Shigella strains, including S. dysenteriae type 1, which produces Shiga toxin.

Social-economic factors and irrational antibiotic use as reasons for antibiotic resistance of bacteria causing common childhood infections in primary healthcare

The most prevalent childhood bacterial infections in primary healthcare are respiratory, gastrointestinal and urogenital infections. The main aim of this paper was to consider factors (socio-economic factors and irrational antibiotic use) that contribute to the development of bacterial resistance, as well as measures that resulted in a reduction of this problem. Computerized search through the Medline of published articles on antibiotic resistance from 1996 to 2011 in English or Serbian was completed in August 2011. Combinations of used terms were antimicrobial/antibacterial/antibiotic and resistance/susceptibility in pediatric/children, and Streptococcus pneumoniae/Streptococci/Haemophilus influenzae/Salmonellae/Escherichia coli/Shigella/Staphylococcus aureus as well as antibiotics/antimicrobials/antibacterials and consumption/utilization/use. In many developing countries, antibiotic dispensing and its use in medicine, cattle breeding and agriculture are inadequately regulated, or existing laws are not being appropriately implemented. In addition, human travel contributes to antimicrobial drug resistance around the world. All of these factors have led to a very high level of bacterial resistance. On the contrary, in countries with a clearly defined and implemented legal framework concerning antibiotic prescribing, dispensing and utilization, the use of antibiotics is under constant surveillance. That resulted in a significantly lower antibacterial resistance. In conclusion, bacterial resistance could be reduced by the implementation of systemic and long-term measures at a country level as well as at all levels of healthcare. In order to reduce bacterial resistance, antibiotic use needs to be precisely regulated, and regulations should be coherent with practice. The international community must have a more active role in solving this global problem.

Live attenuated Shigella dysenteriae type 1 vaccine strains overexpressing shiga toxin B subunit

Shigella dysenteriae serotype 1 (S. dysenteriae 1) is unique among the Shigella species and serotypes in the expression of Shiga toxin which contributes to more severe disease sequelae and the ability to cause explosive outbreaks and pandemics. S. dysenteriae 1 shares characteristics with other Shigella species, including the capability of causing clinical illness with a very low inoculum (10 to 100 CFU) and resistance to multiple antibiotics, underscoring the need for efficacious vaccines and therapeutics. Following the demonstration of the successful attenuating capacity of deletion mutations in the guaBA operon in S. flexneri 2a vaccine strains in clinical studies, we developed a series of S. dysenteriae 1 vaccine candidates containing the fundamental attenuating mutation in guaBA. All strains are devoid of Shiga toxin activity by specific deletion of the gene encoding the StxA subunit, which encodes enzymatic activity. The StxB subunit was overexpressed in several derivatives by either plasmid-based constructs or chromosomal manipulation to include a strong promoter. All strains are attenuated for growth in vitro in the HeLa cell assay and for plaque formation and were safe in the Serény test and immunogenic in the guinea pigs. Each strain induced robust serum and mucosal anti-S. dysenteriae 1 lipopolysaccharide (LPS) responses and protected against wild-type challenge. Two strains engineered to overexpress StxB induced high titers of Shiga toxin neutralizing antibodies. These candidates demonstrate the potential for a live attenuated vaccine to protect against disease caused by S. dysenteriae 1 and potentially to protect against the toxic effects of other Shiga toxin 1-expressing pathogens.

Hemolytic uremic syndrome: new developments in pathogenesis and treatment

Hemolytic uremic syndrome is defined by the characteristic triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. In children, most cases of HUS are caused by Shiga-toxin-producing bacteria, especially Escherichia coli O157:H7. Common vehicles of transmission include ground beef, unpasteurized milk, and municipal or swimming water. Shiga-toxin-associated HUS is a main cause of acute renal failure in young children. Management remains supportive as there is at present no specific therapy to ameliorate the prognosis. Immediate outcome is most often favourable but long-term renal sequelae are frequent due to nephron loss. Atypical HUS represents 5% of cases. In the past 15 years, mutations in complement regulators of the alternative pathway have been identified in almost 60% of cases, leading to excessive complement activation. The disease has a relapsing course and more than half of the patients either die or progress to end-stage renal failure. Recurrence after renal transplantation is frequent.

Enterohaemorrhagic Escherichia coli and Shigella dysenteriae type 1-induced haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS) can be classified according to the aetiology of the different disorders from which it is composed. The most prevalent form is that induced by shigatoxin producing Escherichia coli (STEC) and, in some tropical regions, by Shigella dysenteriae type 1. STEC cause a zoonosis, are widely distributed in nature, enter the food chain in different ways, and show regional differences. Not all STEC are human pathogens. Enterohaemorrhagic E. coli usually cause attachment and effacing lesions in the intestine. This is not essential, but production of a shigatoxin (Stx) is. Because Stx are encoded by a bacteriophage, this property is transferable to naïve strains. Laboratory methods have improved by identifying STEC either via the toxin or its bacteriophage. Shigella dysenteriae type 1 produces shigatoxin, identical to Stx-1, but also has entero-invasive properties that enterohaemorrhagic Escherichia coli (EHEC) do not. Shigella patients risk bacteremia and benefit from early antibiotic treatment, unlike those with EHEC.

Low Risk of Hemolytic Uremic Syndrome after Early Effective Antimicrobial Therapy for Shigella dysenteriae Type 1 Infection in Bangladesh

BACKGROUND

Hemolytic uremic syndrome (HUS) may complicate up to 15% of cases of Shiga toxin (Stx)-expressing enterohemorrhagic Escherichia coli (STEC) O157:H7 infections in children. Administration of antimicrobials has been reported to increase the risk of STEC-associated HUS by >10-fold, presumably by increasing the expression and release of Stx by dying STEC bacteria. Shigella dysenteriae type 1 also expresses Stx. However, the effect of antimicrobial therapy on Stx release and the risk of HUS in humans is unknown.

METHODS

We measured serial stool Stx concentrations before and after administration of antimicrobials in 20 children infected with S. dysenteriae type 1 who had frank dysentery of <72 h duration. We also reviewed the results of 7 shigellosis drug trials performed in Bangladesh during 1988-2000 to estimate the risk of HUS. In these studies, antimicrobials were administered within 96 h after the onset of dysentery.

RESULTS

Stx levels decreased in stool samples obtained from 17 of 20 children after administration of antimicrobial agents; none of the 20 children developed HUS. Of 378 individuals infected with S. dysenteriae type 1 who were enrolled in drug trials (128 adult men [age, 18-60 years] and 250 children [age, 6 months to 15 years]), 351 (93%) received an antimicrobial agent to which the S. dysenteriae organism was susceptible <or=96 h after the onset of symptoms; HUS developed in 1 child. The risk of developing HUS was 0.0026 for all participants (95% confidence interval, <0.001 to 0.015) and was 0.004 for children (95% confidence interval, 0.001-0.022).

CONCLUSION

In persons infected with S. dysenteriae type 1, early administration of effective antibiotics is associated with decreased Stx concentrations in stool and a low risk of developing HUS.