¶ … Micro-Organism: Syghella dysenteriae
Genus: Shigella (Castellani and Chalmers 1919)
Type species: Shigella dysenteriae (Shiga 1897) Castellani and Chalmers 1919 (Approved Lists 1980)
Gammaproteobacteria, from the family of enterobacteriaceae (GBIF.org)
Gram-negative, non-acid-fast bacilli; no spores, no capsules; non-motile; do not posses flagella, rod-shaped bacteria (Todar, 2008-2012)
Picture was obtained from Sciencephoto Library
According to the national Institute of Health, "Shigella dysenteriae serotype 1 (SD1) causes the most severe form of epidemic bacillary dysentery"
Shigella dysenteriae type 1 is rare in the U.S., but it causes epidemics in the developing countries (Todar, 2008-2012)
Shigella dysenteriae is one of the four species of Shigella, also known as group A (World Health Organization, 2005).
The microorganism produces a toxin called Shiga toxin (Bhunia, 2007). I causes shigellosis, characterized by bacillary dysentery (mucoid bloody stool).
Shigella micro-organisms are present in soil and water. They will become infective only in the presence of the "invasion plasmid that will allow it to bind to the epithelial cells of the intestine and a smooth lipopolysaccharide somatic antigen" (Mara, Horan, 2003).
The primary route of transmission is fecal-oral. The bacteria survives in water contaminated with human feces (Bhunia, 2007), for 5-11 days, on bed sheets (for up to seven weeks), kitchen waste (up to 4 days), "in dust particles for 6 weeks at room temperature"(the Graf Laboratory web site). "It grows well on ordinary culture media" with an optimal temperature for cultivation at 37C (Erwin Neter). It survives as a facultative anaerobe (The Graf Laboratory).
Only human and primates can host Shigella. Flies carry it.
The bacteria causes an acute infection of the intestine (Heiman, Bowen). The infection is realized by means of ingestion of fecal material through direct human contact or indirectly, often through contact with infested water and foods or other media. Because it spreads fast and easily, Shigella dysenteriae type 1 often causes epidemics on large areas. The cytotoxin the bacteria produces is very potent and the infections it causes occur more frequently, are more virulent, spread faster and last longer than those the other species of Shigella cause. It also differs from the other Shigella species in its increased resistance to antimicrobials (The World Health Organization, 2005). Shigellosis is responsible for most cases of bloody diarrhea in the world (idem). The developing countries are the most vulnerable and children under five are the main target cases in Shigellosis, with the highest rate of mortailty (idem). The elderly and the malnourished are another two of the most vulnerable categories when it comes to the severity of manifestation and the death threat in case of infection with Syghella Dysenteriae tpe 1. Epidemics occurred and are still likely to brake out in Africa, South Asia and Central America. Epidemics are favored also by the fact that the dose necessary for infection is relatively low: cca 10 to 200 viable organisms (The World Health Organization, 2005, ).
After "breaking in" two processes follow: the bacillus invades the epithelium in the colon and causes inflammatory colitis. "Colitis in the rectosigmoid mucosa, with concomitant malabsorption, results in the characteristic sign of bacillary dysentery: scanty,. unformed stools tinged with blood and mucus" (Hale, Keusch, 1996; Education Portal).
The microbial pathogen Shigella dysenteriae cells can even freezing conditions and exposure to harsh chemicals. They would subside under high temperature exposure and will die under pasteurization (Bhunia). Conditions of overcrowding and poor sanitation as well as hot and humid weather conditions concur to the development and fast spreading of the bacillus.
Incubation: the infection with start manifesting between 1 and 3 days from the moment the bacillus has entered the host organism.
Reproduction
Extremely adapted to reproduce in the colon epithelium. Two plasmid-encoded bacterial protein virulence determinants designated Invasion Plasmid Antigens (Ipa) B. And C. are triggered upon contact with the host cells (Hale,
Keusch, 1996). Another InterCellular Spread (IcsA) protein will also ultimately lead to "intracellular bacterial spread"(idem). Its ability to invade the epithelial host cells, multiply, spread and ultimately kill the infected cells.
Starting with the invasion of a host cell, running to the spread by intracellular multiplication and cell-to-cell spread, finalized with the killing of the initial host, Shigella dysenteriae bacterium has created a completely safe environment, protected from antibody or other antimicrobial factors the host body produces (Evans, Brachman, 1998).
Symptoms
Often, but not always, bloody diarrhea, sometimes watery, along with cramps, vomiting, nausea are some of the most common symptoms. Some other symptoms may be: fever, rectal pain. Patients usually recover in several days. However, complications can increase the severity of a case. One of the most frequent is: the hemolytic-uremic syndrome (HUS). Here the severity varies, between a mild manifestation followed by a quick recovery or a severe one, followed by kidney failure and death (Laboratory Methods for the Diagnosis of Epidemic Dysentery and Cholera, 1999).
Image taken from Medical Microbiology, 1996, ed. Baron S.
Prevention
Since the main route of transmission is fecal-oral, strict hygiene rules...
It includes frequent hand washing with soap, food and water precautions. Health education is very important in raising awareness to the vital role hygiene plays in preventing the outbreak of an epidemic. Properly chlorinated water and a correctly structured and well maintained piped water system significantly contribute to the reduction of the incidence. Other prevention factors are: the promotion of safe water and food transportation and storage, individual food handling safety rules, breastfeeding, measles immunization, safe disposal of waste (WHO).
Treatment
Antimicrobial. Upon susceptibility testing of local Sd1 strains and under the condition that the recommended antibiotic is effective against at least 80% of the strains, a treatment policy could include one of the following: ampicillin, trimethoprim-sulfamethoxazole, nalidixic acid, pivmecillinam, ciprofloxacin norfloxacin, enoxacin. The bacillus has become more and more resistant to the two first antimicrobial agents, thus the third one, the nalidixic acid was considered as the safest choice for treatment. Unfortunately, this is no longer the case. As Jane Perlez was writing in New York Times in 1994: "One reason that shigella dysentery presents such a danger is that the bacterium that causes it, S. dysenteriae type 1, has become largely resistant to antibiotics, including Negram, whose generic name is nalidixic acid."
Oral rehydration is also important to prevent intravenous rehydration or death. Dehydration as one of the accompanying symptoms, can lead to death, with an increased rapidity in young children. The rehydration solutions can be prepared at home, following the food handling and processing rules and with safe water, according to a simple formula (WHO).
Anti-pyretic drugs should be administered to treat fever symptoms and analgesics to treat pain. For children of up to five years of age, zinc supplements are recommended
History
The bacterium has been first isolated and identified in the stool samples of patients during an epidemic outbreak in Japan, in 1898, by dr. Kioshi Shiga, who gave the name to the genus. Shiga identified the Shigella dysenteriae 1 bacterium and soon after his results have been confirmed in other countries around the world.
But, the history of dysentery goes a long way back in history. The disease was reported in 1823, by George Ballingall to be responsible for three fourths of all the deaths reported in India. The disease can be identified in ancient texts. Pandemics of shigellosis seem to be as old as humanity and there is still no vaccine against it.
Image taken from Nature Reviews. Microbiology. http://www.nature.com/nrmicro/journal/v5/n7/fig_tab/nrmicro1662_F1.html
Alfred S. Evans, Philip S. Brachman. 1998. Bacterial Infections of Humans: Epidemiology and Control. Springer Science & Business Media
Ballingall, Evans. 1823. Black. Practical observations on fever, dysentery, and liver complaints: as they occur amongst the European troops in India; to which is annexed an essay on syphilis.
Bhunia, Arun. 2007. Foodborne Microbial Pathogens: Mechanisms and Pathogenesis. Springer Science & Business Media
Duncan, Mara. Horan, Nigel J. 2003. Handbook of Water and Wastewater Microbiology. Academic Press
Hale, Thomas L. Keusch, Gerald T. Medical Microbiology, 4th edition. Chapter 22, Shigella. Retrieved from: http://www.ncbi.nlm.nih.gov/books/NBK8038 /, on Nov. 2nd, 2014
Neter, Erwin. 1942. THE GENUS SHIGELLA. PMC. U.S. national Library of Medicine. Retrieved from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC440856/?page=1, on Nov 1st, 2014
Perlez, Jane.1994. The New York Times. A Stubborn Killer of Refugees: Dysentery. Retrieved from: http://www.nytimes.com/1994/08/05/world/a-stubborn-killer-of-refugees-dysentery.html?module=Search&mabReward=relbias%3Aw%2C%7B%222%22%3A%22RI%3A16%22%7D, on ov 2nd, 2014
Todar, Kenneth. Todar's Online Textbook of Bacteriology. "Shigella and Shigellosis." Retrieved from: http://textbookofbacteriology.net/Shigella.html on Nov 1st, 2014
Nature Reviews. Microbiology. Retrieved from: http://www.nature.com/nrmicro/journal/v5/n7/fig_tab/nrmicro1662_F1.html on, Nov. 2nd, 2014
Education Portal. Dysentery and the Bacteria Shigella: Symptoms & Causes. Retrieved from: http://education-portal.com/academy/lesson/dysentery-and-the-bacteria-shigella-symptoms-causes.html#lesson on, Oct 30th, 2014
GBIF.org. Shigella dysenteriae (Shiga, 1897). Retrieved from: http://www.gbif.org/species/117114047 on Nov 2nd 2014
The Graf Laboratory. University of Connecticut - Department of Molecular and Cell Biology. Student Presentation. Shigella dysenteriae. Retrieved from: http://web.uconn.edu/mcbstaff/graf/Student%20presentations/Shigella/Shigella.html, on Nov 1st, 2014
Watson, John C. Hlavsa, Michele C.. Griffin. Patricia M. 2013. "Food and Water Precausions." Travelers Health. Centers for Disease Control and Prevention. Retrieved from: http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/food-and-water-precautions
World Health Organization. 2005. "Guidelines for the control of shigellosis, including epidemics due to Shigella dysenteriae type 1." Retrieved from: http://whqlibdoc.who.int/publications/2005/9241592330.pdf, on Nov 2nd, 2014
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2. http://www.gbif.org/species/117114047
3. http://www.sciencephoto.com/media/11549/view
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