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Shigella & Shigellosis
|Shigellosis, also known as bacillary
dysentery in its most severe manifestation, is a foodborne illness
caused by infection by bacteria of the genus Shigella. Shigellosis
rarely occurs in animals other than humans and other primates like
monkeys and chimpanzees. The causative organism is frequently found in
water polluted with human feces, and is transmitted via the fecal-oral
route. The usual mode of transmission is directly person-to-person
hand-to-mouth, in the setting of poor hygiene among children. In some
strains ten to fifteen (10-15)% of people affected will die. In the
developing world, Shigella causes approximately 165 million cases of
severe dysentery and more than 1 million deaths each year, mostly in
children in the developing world. Shigella also causes approximately
580,000 cases annually among travelers and military personnel from
Symptoms may range from mild abdominal discomfort to full-blown
dysentery characterized by cramps, diarrhea, fever, vomiting, blood,
pus, or mucus in stools or tenesmus. Onset time is 12 to 50 hours.
Shigella can be transmitted through food. Food known to do so includes
salads (potato, tuna, shrimp, macaroni, and chicken), raw vegetables,
milk and dairy products, and meat. Contamination of these foods is
usually through the fecal-oral route. Fecally contaminated water and
unsanitary handling by food handlers are the most common causes of
Shigella is a genus of Gram-negative,
non-spore forming rod-shaped bacteria
to Escherichia coli and Salmonella. The causative agent of human
shigellosis, Shigella cause disease in primates, but not in other
mammals. It is only naturally found in humans and apes. During
infection, it typically causes dysentery.
Shigella infection is typically via
contamination); depending on age and condition of the host as few as
ten bacterial cells can be enough to cause an infection. Shigella
causes dysentery that results in the destruction of the epithelial
cells of the intestinal mucosa in the cecum and rectum. Some strains
produce enterotoxin and Shiga toxin, similar to the verotoxin of E.
coli O157:H7. Both Shiga toxin and verotoxin are associated with
causing hemolytic uremic syndrome.
Shigella invade the host through epithelial cells of the large intestine.
Using a Type III secretion system
acting as a biological syringe, the bacterium injects IpaD protein into
cell, triggering bacterial invasion and the subsequent lysis of
vacuolar membranes using IpaB and IpaC proteins. It utilizes a
mechanism for its motility by which its IcsA protein triggers actin
polymerization in the host cell (via N-WASP recruitment of Arp2/3 complexes) in a "rocket" propulsion
fashion for cell-to-cell spread. The most common symptoms are diarrhea,
fever, nausea, vomiting, stomach cramps, flatulence, and constipation.
The stool may contain blood, mucus, or pus. In rare cases, young
children may have seizures.
Symptoms can take as long as a week to show up, but most often begin
two to four days after ingestion. Symptoms usually last for several
days but can last for weeks. Shigella is implicated as one of the
pathogenic causes of reactive arthritis worldwide.
form of dysentery can be
treated with ampicillin, TMP-SMX, or fluoroquinolones such as ciprofloxacin and
of course rehydration.
Did You Know?
|Shigellosis is a very
common malady suffered by individuals with Acquired Immune Deficiency
is a more common and serious condition in the developing world.
|An estimated 18,000 cases
of shigellosis occur annually in the United States. Infants, the
elderly, and the infirm are susceptible to the severest symptoms of
disease, but all humans are susceptible to some degree.
|Infections are associated
mucosal ulceration, rectal bleeding, drastic dehydration; fatality may
be as high as 10-15% with some strains. Reiter's disease and hemolytic
uremic syndrome are possible sequelae that have been reported in the
aftermath of shigellosis.
of the Shigella genomes includes a virulence plasmid that encodes
conserved primary virulence determinants. The Shigella chromosomesE.
coli K12 strain MG1655 share most of their genes with that of E. coli
K12 strain MG1655.
|Type three secretion
system (often written Type III secretion system and abbreviated TTSS or
T3SS) is a protein structure, an organelle, found in several
The structure is used to secrete proteins that help the bacteria infect
multicellular, eukaryotic organisms. The proteins are secreted directly
from the bacterial cell into the cells of the organism to be infected
(the host) using a needle-like structure which is the hallmark of the