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| Bacillary dysentery | |
|---|---|
| Specialty | Infectious diseases  |
Bacillary dysentery is a type ofdysentery, and is a severe form ofshigellosis. It is associated with species of bacteria from the familyEnterobacteriaceae.[1] The term is usually restricted toShigella infections.[2]
Shigellosis is caused by one of several types ofShigellabacteria.[3] Three species are associated with bacillary dysentery:Shigella sonnei,Shigella flexneri andShigella dysenteriae.[4] A study in China indicated thatShigella flexneri 2a was the most commonserotype.[5]
Salmonellosis caused bySalmonella enterica (serovarTyphimurium) has also been described as a cause of bacillary dysentery,[citation needed] though this definition is less common. It is sometimes listed as an explicitdifferential diagnosis of bacillary dysentery, as opposed to a cause.[6]
Bacillary dysentery should not be confused withdiarrhea caused by other bacterial infections. One characteristic of bacillary dysentery isblood in stool,[7] which is the result of invasion of themucosa by the pathogen.
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Transmission isfecal-oral and is remarkable for the small number of organisms that may cause disease (10 ingested organisms cause illness in 10% of volunteers, and 500 organisms cause disease in 50% of volunteers).Shigella bacteria invade the intestinal mucosal cells but do not usually go beyond the lamina propria. Dysentery is caused when the bacteria escape the epithelial cell phagolysosome, multiply within the cytoplasm, and destroy host cells. Shiga toxin causes hemorrhagiccolitis andhemolytic-uremic syndrome by damaging endothelial cells in the microvasculature of the colon and the glomeruli, respectively. In addition, chronic arthritis secondary toS. flexneri infection, calledreactive arthritis, may be caused by a bacterial antigen; the occurrence of this syndrome is strongly linked to HLA-B27 genotype, but the immunologic basis of this reaction is not understood.[citation needed]
Specimen: Fresh stool is collected.
Culture: Specimen is inoculated on selective media likeMacConkey's agar,DCA,XLD agar. Selenite F broth(0.4%) is used as enrichment medium which permits the rapid growth of enteric pathogens while inhibiting the growth of normal flora likeE. coli for 6–8 hours. Subculture is done on the solid media from selenite F broth. All the solid media are incubated at 37 degrees for 24 hours.
Cultural characteristics: Colorless (NLF) colonies appear on MacConkey's agar which are further confirmed by gram staining, hanging drop preparation and biochemical reactions.
Dysentery is initially managed by maintaining fluid intake usingoral rehydration therapy. If this treatment cannot be adequately maintained due to vomiting or the profuseness of diarrhea, hospital admission may be required forintravenous fluid replacement. Ideally, no antimicrobial therapy should be administered until microbiological microscopy and culture studies have established the specific infection involved. When laboratory services are not available, it may be necessary to administer a combination of drugs, including an amoebicidal drug to kill theparasite and anantibiotic to treat any associated bacterialinfection.
Anyone with bloody diarrhea needs immediate medical help. Treatment often starts with an oral rehydrating solution—water mixed with salt and carbohydrates—to prevent dehydration. (Emergency relief services often distribute inexpensive packets of sugars and mineral salts that can be mixed with clean water and used to restore lifesaving fluids in dehydrated children gravely ill from dysentery.)
IfShigella is suspected and it is not too severe, the doctor may recommend letting it run its course—usually less than a week. The patient will be advised to replace fluids lost through diarrhea. If the infection is severe, the doctor may prescribe antibiotics, such asciprofloxacin or TMP-SMX (Bactrim). Unfortunately, many strains ofShigella are becoming resistant to common antibiotics, and effective medications are often in short supply in developing countries. If necessary, a doctor may have to reserve antibiotics for those at highest risk for death, including young children, people over 50, and anyone suffering from dehydration or malnutrition.
No vaccine is available. There are severalShigellavaccine candidates in various stages of development that could reduce the incidence of dysentery in endemic countries, as well as in travelers withtraveler's diarrhea.[8]
The bacterium causing shigellosis is named afterKiyoshi Shiga, a Japanese researcher who discovered it in 1897.
