Shigellosis in Mozambique: the 1993 outbreak rehabilitation--a follow-up study

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

A piglet model of acute gastroenteritis induced by Shigella dysenteriae Type 1

BACKGROUND

The lack of a standardized laboratory animal model that mimics key aspects of human shigellosis remains a major obstacle to addressing questions about pathogenesis, screening therapeutics, and evaluation of vaccines.

METHODS

We characterized a piglet model for Shigella dysenteriae type 1.

RESULTS

Piglets developed acute diarrhea, anorexia, and dehydration, which could often be fatal, with symptom severity depending on age and dose. Bacteria were apparent in the lumen and on the surface epithelium throughout the gut initially, but severe mucosal damage and bacterial cellular invasion were most profound in the colon. Detached necrotic colonocytes were present in the lumen, with inflammatory cells outpouring from damaged mucosa. High levels of interleukin (IL)-8 and IL-12 were followed by high levels of other proinflammatory cytokines. Elevated levels of tumor necrosis factor-alpha, IL-1beta, IL-6, and IL-10 were detected in feces and in gut segments from infected animals. Bacteria were present inside epithelial cells and within colonic lamina propria. In contrast, an isogenic strain lacking Shiga toxin induced similar but milder symptoms, with moderate mucosal damage and lower cytokine levels.

CONCLUSION

We conclude that piglets are highly susceptible to shigellosis, providing a useful tool with which to compare vaccine candidates for immunogenicity, reactogenicity, and response to challenge; investigate the role of virulence factors; and test the efficacy of microbial agents.

Epidemiology and clinical presentation of shigellosis in children less than five years of age in rural Mozambique

Rectal swabs were collected from 1354 children <5 years of age with diarrhea attending Manhiça District Hospital and from 227 healthy community controls. Shigellosis incidence was high among children aged 12-47 months (488.4/10(5) child-years at risk). Fever and dysentery were prominent clinical findings. Shigella was more frequently isolated from cases than controls (6.7% versus 0.4%, P = 0.004), and from dysentery than nondysenteric diarrhea (24.1% versus 3.5%, P < 0.001). Shigella flexneri 2a, S. sonnei, and S. flexneri 6, were the most prevalent serotypes.

Clinical trials of Shigella vaccines: two steps forward and one step back on a long, hard road

More than 50 years of research has yielded numerous Shigella vaccine candidates that have exemplified both the promise of vaccine-induced prevention of shigellosis and the impediments to developing a safe and effective vaccine for widespread use, a goal that has yet to be attained. This Review discusses the most advanced strategies for Shigella vaccine development, the immune responses that are elicited following disease or vaccination, the factors that have accelerated or impeded Shigella vaccine development and our ideas for the way forward.

Part II. Analysis of data gaps pertaining to Shigella infections in low and medium human development index countries, 1984-2005

The global incidence of Shigella infection has been estimated at 80-165 million episodes annually, with 99% of episodes occurring in the developing world. To identify contemporary gaps in the understanding of the global epidemiology of shigellosis, we conducted a review of the English-language scientific literature from 1984 to 2005, restricting the search to low and medium human development countries. Our review yielded 11 population-based studies of Shigella burden from seven countries. No population-based studies have been conducted in sub-Saharan Africa or in low human development countries. In studies done in all age groups, Shigella incidence varied from 0.6 to 107 episodes/1000 person-years. S. flexneri was the most commonly detected subgroup in the majority of studies. Case-fatality rates ranged from 0% to 2.6% in population-based studies and from 0% to 21% in facility-based studies. This review highlights the large gaps in data on the burden of Shigella infections for low human development index countries and, more specifically, for sub-Saharan Africa.

Using European travellers as an early alert to detect emerging pathogens in countries with limited laboratory resources

Background

The volume, extent and speed of travel have dramatically increased in the past decades, providing the potential for an infectious disease to spread through the transportation network. By collecting information on the suspected place of infection, existing surveillance systems in industrialized countries may provide timely information for areas of the world without adequate surveillance currently in place. We present the results of a case study using reported cases of Shigella dysenteriae serotype 1 (Sd1) in European travellers to detect "events" of Sd1, related to either epidemic cases or endemic cases in developing countries.

Methods

We identified papers from a Medline search for reported events of Sd1 from 1940 to 2002. We requested data on shigella infections reported to the responsible surveillance entities in 17 European countries. Reports of Sd1 from the published literature were then compared with Sd1 notified cases among European travellers from 1990 to 2002.

Results

Prior to a large epidemic in 1999–2000, no cases of Sd1 had been identified in West Africa. However, if travellers had been used as an early warning, Sd1 could have been identified in this region as earlier as 1992.

Conclusion

This project demonstrates that tracking diseases in European travellers could be used to detect emerging disease in developing countries. This approach should be further tested with a view to the continuous improvement of national health surveillance systems and existing European networks, and may play a significant role in aiding the international public health community to improve infectious disease control.

Molecular epidemiology of multidrug-resistant Shigella dysenteriae type 1 causing dysentery outbreaks in Central African Republic, 2003–2004

Shigella dysenteriae type 1 (Sd1) represents a particular threat in developing countries because of the severity of the infection and its epidemic potential. Antimicrobial susceptibility testing and molecular subtyping by pulsed-field gel electrophoresis (PFGE) and plasmid profiling (PP) of Sd1 isolates collected during two dysentery outbreaks (2013 and 445 cases of bloody diarrhoea) in Central African Republic (CAR) during the period 2003-2004 were reported. Eleven Sd1 comparison strains (CS) acquired by travellers or residents of Africa (n=10) or Asia (n=1) between 1993 and 2003 were also analysed. The 19 Sd1 isolates recovered from CAR outbreaks were multidrug resistant, although susceptible to quinolones and fluoroquinolones. Molecular subtyping by PFGE was more discriminatory than PP. The PFGE using XbaI and NotI restriction enzymes indicated that the two outbreaks were due to two different clones and also revealed a genetic diversity among the CS recovered from outbreak or sporadic cases between 1993 and 2003. This study was the result of a fruitful collaboration between field physicians and microbiologists. The data collected will serve as the basis for establishing long-term monitoring of Sd1 in CAR.

Case management of a multidrug-resistant Shigella dysenteriae serotype 1 outbreak in a crisis context in Sierra Leone, 1999-2000

From December 1999 to the end of February 2000, 4218 cases of dysentery were reported in Kenema district, southeastern Sierra Leone, by a Médecins Sans Frontières team operating in this region. Shigella dysenteriae serotype 1 was isolated from the early cases. The overall attack rate was 7.5% but higher among children under 5 years (11.2%) compared to the rest of the population (6.8%) (RR = 1.6; 95% CI 1.5-1.8). The case fatality ratio was 3.1%, and higher for children under 5 years (6.1% vs. 2.1%) (RR = 2.9; 95% CI 2.1-4.1). A case management strategy based on stratification of affected cases was chosen in this resource-poor setting. Patients considered at higher risk of death were treated with a 5 day ciprofloxacin regimen in isolation centres. Five hundred and eighty-three cases were treated with a case fatality ratio of 0.9%. Patients who did not have signs of severity when seen by health workers were given hygiene advice and oral rehydration salts. This strategy was effective in this complex emergency.

Factors contributing to the emergence of Escherichia coli O157 in Africa

In 1992, a large outbreak of bloody diarrhea caused by Escherichia coli O157 infections occurred in southern Africa. In Swaziland, 40,912 physician visits for diarrhea in persons ages >5 years were reported during October through November 1992. This was a sevenfold increase over the same period during 1990-91. The attack rate was 42% among 778 residents we surveyed. Female gender and consuming beef and untreated water were significant risks for illness. E. coli O157:NM was recovered from seven affected foci in Swaziland and South Africa; 27 of 31 patient and environmental isolates had indistinguishable pulsed-field gel electrophoresis patterns. Compared with previous years, a fivefold increase in cattle deaths occurred in October 1992. The first heavy rains fell that same month (36 mm), following 3 months of drought. Drought, carriage of E. coli O157 by cattle, and heavy rains with contamination of surface water appear to be important factors contributing to this outbreak.

An epidemic of bloody diarrhea: Escherichia coli O157 emerging in Cameroon?

Between November 1997 and April 20, 1998, bloody diarrhea sickened 298 persons in Cameroon. Laboratory investigation of the epidemic (case-fatality rate, 16.4%) documented amoebiasis in one of three patients and three types of pathogens: multidrug-resistant Shigella dysenteriae type 1, S. boydii, and enterohemorrhagic Escherichia coli. We report the first isolation of E. coli O157:H7 in Cameroon and the second series of cases in the Central African region.

Epidemic dysentery in western Kenya

This paper describes the epidemiology of a probable Shigella dysenteriae type 1 dysentery epidemic in western Kenya. A retrospective record review over 2 years of all cases of dysentery, amoebiasis and diarrhoea was carried out in 13 healthcare facilities in the Rarieda Division of Nyanza province. Of the 3301 cases recorded, 2191 were dysentery, giving a cumulative 2 years incidence rate for dysentery of 4%. The epidemic began in December 1994 and peaked in February 1995, coinciding with the very dry season. One location in the area had an overall attack rate of 9.3%, double that of other locations. Highest rates were in children aged < 5 years and in persons > 15 years old. S. dysenteriae type 1, with its increasing multiantibiotic resistance, is a continuing threat to the health of people in this region; this area may be suitable for intensive, prospective surveillance as a prelude to a Shigella vaccine trial.