A patient with paratyphoid A fever: an emerging problem in Asia and not always a benign disease

Heterologous expression of the Salmonella enterica serovar Paratyphi A stk fimbrial operon suggests a potential for repeat sequence-mediated low-frequency phase variation

Fimbriae mediate adhesion of Salmonella enterica organisms to the intestinal epithelium, which is an essential step in the pathogenesis process preceding invasion and/or systemic spread. In addition, Salmonella fimbrial genes transcripts were detected in the blood samples from Salmonella infected human patients, which supports the proposal that fimbriae play a role in invasive Salmonella infections. In this study, BlastN-based interrogation of the NCBI bacterial genome database and PCR investigation of Salmonella serovars have shown that the S. Paratyphi A stkF gene and/or the whole stk fimbrial gene cluster is present in about ~30% of S. enterica serovars investigated up to date. Furthermore, bioinformatics and phenotypic characterization have revealed that the stk fimbrial operon belongs to the chaperone/usher-γ4- fimbrial clade and that it encodes a mannose-sensitive hemagglutinating fimbrial structure. The latter trait is typical of type 1 fimbriae, in which fimbrial phase variation is common. The observed intragenic, 26 bp tandem repeat triplication event in stkF would suggest that slipped-strand mispairing and/or recombination within a signature stkF-borne tandem repeat motif as a likely mechanism for a form of low-frequency phase switching at the translational level leading to allelic OFF forms, hence the inability of production and/or absence of fimbriae by EM-examination on E. coli HB101/pUCstk-stkF_OFFv2. The in vitro profile of marked anti-StkF-mediated opsonophagocytosis and complement-mediated killing activity observed coupled with the mice immunogenicity profile strongly supports further investigation of StkF as a potential Salmonella vaccine candidate.

Preventing invasive salmonellosis in children through vaccination

INTRODUCTION

Vaccination is an important strategy to control endemic enteric fever (EF) and to interrupt transmission during outbreaks. The main aim of this paper is to discuss the efficacy of available EF vaccines in children and to highlight novel vaccination possibilities against EF and non-typhoid invasive salmonelloses.

AREAS COVERED

Two types of typhoid vaccines are presently available in the industrialized world. One of these vaccines is administered parenterally and is based on the virulence-associated (Vi) capsular polysaccaride of Salmonella typhi. The second vaccine is based on a live attenuated strain of the pathogen and is given orally. In addition, a Vi-tetanus toxoid conjugated vaccine is currently licensed in India; however, it is not available anywhere else. Expert commentary: Unfortunately, only typhoid fever is addressed by the currently licensed typhoid vaccines. Moreover, they are unsuitable for infants and remain a possible aid for reducing the risk of EF only in older subjects. They should be used in developing countries with endemic EF. New vaccines able to confer long-term protection to subjects in the first years of life and those with immature immune systems could significantly reduce incidence rates of EF in younger children. Vi-conjugate preparations are promising solutions in this regard.

Increasing rates of Salmonella Paratyphi A and the current status of its vaccine development

Enteric fever caused by Salmonella enterica serovar Typhi and Salmonella enterica serovar Paratyphi is still a major disease burden mainly in developing countries. Previously, S. Typhi was believed to be the major cause of enteric fever. The real situation is now becoming clear with reports emerging from many Asian countries of S. Paratyphi, mostly S. Paratyphi A, causing a substantial number of cases of enteric fever. Although there have been advances in the use of the currently available typhoid vaccines and in the development of newer typhoid vaccines, paratyphoid vaccine development is lagging behind. Since the disease caused by S. Typhi and S. Paratyphi are clinically indistinguishable and are commonly termed 'enteric' fever, it will be necessary to have a vaccine available against both S. Typhi and S. Paratyphi A as a bivalent 'enteric fever vaccine'.

Vaccines for typhoid fever and other salmonelloses

PURPOSE OF REVIEW

This review summarizes the recent advances in vaccination against Salmonella enterica serovar Typhi and highlights the data supporting the development of next generation vaccines to address paratyphoid fever and invasive nontyphoidal Salmonella (iNTS) disease.

RECENT FINDINGS

There has been increasing awareness of the disease burden caused by S. Typhi particularly in Africa and greater recognition of S. Paratyphi A's contribution to enteric fever episodes throughout Asia. Groups have been working to improve the existing typhoid vaccines and provide comprehensive data on the feasibility of their implementation in endemic settings. These data have resulted in modifications to the recommendations for typhoid vaccination in traveller markets and endemic settings, and has also led to the development of S. Paratyphi A vaccine components that can be combined with existing typhoid vaccines to generate bivalent formulations against enteric fever. The epidemiology of iNTS serovars as cause of appreciable morbidity and mortality in Africa, and the need for vaccines, has also become more widely appreciated.

SUMMARY

Current typhoid vaccines, although moderately effective for short periods of time, cannot be used in all age groups and only target one of the clinically relevant Salmonella serovars. Greater effort must be placed on the development and implementation of improved vaccines for the disease burden resulting from Typhi, Paratyphi A or iNTS infections.

Multifaceted support for a new medical school in Nepal devoted to rural health by a Canadian Faculty of Medicine and Dentistry

Nepal and Alberta are literally a world apart. Yet they share a common problem of restricted access to health services in remote and rural areas. In Nepal, urban-rural disparities were one of the main issues in the recent civil war, which ended in 2006. In response to the need for improved health equity in Nepal a dedicated group of Nepali physicians began planning the Patan Academy of Health Sciences (PAHS), a new health sciences university dedicated to the education of rural health providers in the early 2000s.

Beginning with a medical school the Patan Academy of Health Sciences uses international help to plan, deliver and assess its curriculum. PAHS developed an International Advisory Board (IAB) attracting international help using a model of broad, intentional recruitment and then on individuals’ natural attraction to a clear mission of peace-making through health equity. Such a model provides for flexible recruitment of globally diverse experts, though it risks a lack of coordination. Until recently, the PAHS IAB has not enjoyed significant or formal support from any single international institution.

However, an increasing number of the international consultants recruited by PAHS to its International Advisory Board are from the University of Alberta in Edmonton, Alberta, Canada (UAlberta). The number of UAlberta Faculty of Medicine and Dentistry members involved in the project has risen to fifteen, providing a critical mass for a coordinated effort to leverage institutional support for this partnership. This paper describes the organic growth of the UAlberta group supporting PAHS, and the ways in which it supports a sister institution in a developing nation.

Trends in Importation of Communicable Diseases into Singapore

Introduction: Singapore is a transition country in Southeast Asia that is both vulnerable and receptive to the introduction and re-introduction of imported communicable diseases. Materials and Methods: For a 10-year period between 1998 and 2007 we studied the trend, epidemiological characteristics, proportion of imported versus local transmission of malaria, viral hepatitis (hepatitis A and E), enteric fevers (typhoid and paratyphoid), cholera, chikungunya and SARS. Results: Of a total of 4617 cases of the above selected diseases notified in Singapore, 3599 (78.0%) were imported. The majority of the imported cases originated from Southeast Asia and the Indian subcontinent. Malaria constituted the largest bulk (of which 95.9% of the 2126 reported cases were imported), followed by hepatitis A (57.1% of 1053 cases imported), typhoid (87.6% of 596 cases imported), paratyphoid (87.6% of 241 cases imported), and hepatitis E (68.8% of 231 cases imported). Furthermore, there were 14 cases of imported cholera, 6 cases of imported severe acute respiratory syndrome (SARS) and 13 cases of imported chikungunya. Conclusion: This study underlines that diseases such as malaria, viral hepatitis and enteric fever occur in Singapore mainly because of importation. The main origin of importation was South and Southeast Asia. The proportion of imported diseases in relation to overall passenger traffic has decreased over the past 10 years. Key words: Chikungunya, Cholera, Hepatitis A and E, Imported diseases, Malaria, Paratyphoid, SARS, Singapore, Typhoid fever

An outbreak of Salmonella Paratyphi A in a boarding school: a community-acquired enteric fever and carriage investigation

Salmonella Paratyphi A (SPA) is rapidly becoming a common cause of enteric fever in South East Asia. A large outbreak of SPA occurred in a boarding middle school in China in 2004. There were 394 suspected cases; 95·5% were students. The highest incidence was in the youngest children (7th grade). Forty-four of 151 (29%) blood cultures and 4/54 (7·4%) rectal swabs were positive for SPA; three were from kitchen workers. The geometric mean levels of serum IgG anti-lipopolysaccharide (anti-LPS) from patients was higher than from healthy individuals [35·25 vs. 5·20 ELISA units (EU), P<0·001]. A kitchen worker with a positive rectal swab, negative blood culture and a high level of serum IgG anti-LPS (529·65 EU), was identified as a possible SPA carrier. No SPA was isolated from water or food samples. A survey of students' habits indicated drinking unboiled water as being the main reason for contracting the disease. Hand washing was the second most important factor. A food handler with possible SPA carriage could also have been a risk factor. Attention to maintaining a safe water supply, enhancing food-handler hygiene and proper hand washing can help to prevent similar outbreaks in the future.

Simple Liver Cyst as a Focus of Salmonella paratyphi Abscess: A Case Report

Salmonellosis, endemic in various part of the world, is considered a differential diagnosis in a tropical traveller. Although it usually presents as gastroenteritis, its various clinical syndromes may vary from mild gastroenteritis to severe septicaemia including abscess formation, the later two being the most common cause of morbidity and mortality. Here we present a patient who returned to the UK after an overseas trip and was diagnosed with a pyogenic liver abscess with Salmonella paratyphi at a site of a pre-existing simple liver cyst.