Shigella

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Shigella

• What is shigellosis?
• Shigellosis is an infectious disease caused by a
  group of bacteria called Shigella. Most who are
  infected with Shigella develop diarrhea, fever,
  and stomach cramps starting a day or two after
  they are exposed to the bacterium. The diarrhea
  is often bloody. Shigellosis usually resolves in
  5 to 7 days. In some persons, especially young
  children and the elderly, the diarrhea can be so
  severe that the patient needs to be hospitalized.
  A severe infection with high fever may also be
  associated with seizures in children less than 2
  years old. Some persons who are infected may have
  no symptoms at all, but may still pass the
  Shigella bacteria to others.
• Shigellosis is responsible for death between
  600,000 to 1.1 million per year.
• The number of shigellosis cases worldwide are
  more than 165 million.

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Shigella

• What sort of germ is Shigella?
• The Shigella germ is a family of bacteria that
  can cause diarrhea in humans. They are
  microscopic living creatures that pass from
  person to person. Shigella were discovered over
  100 years ago by a Japanese scientist named
  Shiga, for whom they are named. There are several
  different kinds of Shigella bacteria Shigella
  sonnei, also known as "Group D" Shigella,
  accounts for over two-thirds of the shigellosis
  in the United States. A second type, Shigella
  flexneri, or "group B" Shigella, accounts for
  almost all of the rest. Other types of Shigella
  are rare in this country, though they continue to
  be important causes of disease in the developing
  world. One type found in the developing world,
  Shigella dysenteriae type 1, causes deadly
  epidemics there.

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Shigella

• The bacterial (Shigella) invasion of colonic
  epithelial cells eventually leads to death of the
  infected cells and spreading of infection leads
  to abscess formation seen in the patients. The
  extensive cell death and tissue destruction at
  this site leads to an intense inflammatory
  response.
• Thus the blood and mucus in dysentery stools as
  well as accompanying fever can be directly
  related to invasion, intracellular replication
  and spread of shigella in the colonic tissue.

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Shigella

• Shigella are Gram-negative, nonmotile,
  facultatively anaerobic, nonsporeforming
  rod-shaped bacteria. The illness caused by
  Shigella (shigellosis) accounts for less than 10
  of the reported outbreaks of foodborne illness in
  this country. Shigella rarely occurs in animals
  principally a disease of humans except other
  primates such as monkeys and chimpanzees. The
  organism is frequently found in water polluted
  with human feces.

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Shigella

• Symptoms -- Abdominal pain cramps diarrhea
  fever vomiting blood, pus, or mucus in stools
  tenesmus. Onset time -- 12 to 50 hours.
• Infective dose -- As few as 10 cells depending on
  age and condition of host. The Shigella spp. are
  highly infectious agents that are transmitted by
  the fecal-oral route.

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Shigella

• Pathology
• The disease is caused when virulent Shigella
  organisms attach to, and penetrate, epithelial
  cells of the intestinal mucosa. After invasion,
  they multiply intracellularly, and spread to
  contiguous epithelial cells resulting in tissue
  destruction. Some strains produce enterotoxin and
  Shiga toxin (very much like the verotoxin of E.
  coli O157H7).
• Large intestine colonization by Shigella- uptake
  into epithelial cells- invasion of lymphoid M
  cells- lysis of phagocytic vacuoles- replication
  of bacteria- use of actin filament of cells to
  invade nearby cells- looks like a very very smart
  program to attack the colon. Secretion of invasin
  and transport of this to outside seems again a
  smart program. We need to learn how nature
  devised such programs if ever we want to fight
  diseases.

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Shigella

• Complications
• Infections are associated with mucosal
  ulceration, rectal bleeding
• drastic dehydration fatality may be as high as
  10-15 with some strains.
• Reiter's disease, reactive arthritis, and
  hemolytic uremic syndrome are
• possible sequelae that have been reported in the
  aftermath of shigellosis.
• Persons with diarrhea usually recover completely,
  although it may be several months before their
  bowel habits are entirely normal. About 3 of
  persons who are infected with one type of
  Shigella, Shigella flexneri, will later develop
  pains in their joints, irritation of the eyes,
  and painful urination. This is called Reiter's
  syndrome. It can last for months or years, and
  can lead to chronic arthritis which is difficult
  to treat. Reiter's syndrome is caused by a
  reaction to Shigella infection that happens only
  in people who are genetically predisposed to it.
• Once someone has had shigellosis, they are not
  likely to get infected with that specific type
  again for at least several years. However, they
  can still get infected with other types of
  Shigella.

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Shigella

• Associated Foods
• Salads (potato, tuna, shrimp, macaroni, and
  chicken), raw vegetables, milk and dairy
  products, and poultry. 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 contamination. Houseflies are passive
  vectors with Shigella either passing through the
  gut of flies or through the surfaces.

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Shigella

• Detection
• Shigella are not associated with any food and are
  introduced into foods by poor hygiene practices.
• Bacteriological methods. DNA based methods- use
  of oligos to probe the plasmids, PCR, immunolgy

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Shigella

• Treatment
• Shigellosis can usually be treated with
  antibiotics. The antibiotics commonly used for
  treatment are ampicillin, trimethoprim
  /sulfamethoxazole (also known as Bactrim or
  Septra), nalidixic acid, or ciprofloxacin.
  Appropriate treatment kills the Shigella bacteria
  that might be present in the patient's stools,
  and shortens the illness. Unfortunately, some
  Shigella bacteria have become resistant to
  antibiotics and using antibiotics to treat
  shigellosis can actually make the germs more
  resistant in the future. Persons with mild
  infections will usually recover quickly without
  antibiotic treatment. Therefore, when many
  persons in a community are affected by
  shigellosis, antibiotics are sometimes used
  selectively to treat only the more severe cases.
  Antidiarrheal agents such as loperamide
  (Imodium) or diphenoxylate with atropine
  (Lomotil) are likely to make the illness worse
  and should be avoided.

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Shigella

• Prevention
• There is no vaccine. But we should demand it
  after all it is public health we are talking
  about.
• Wash hands with soap carefully and frequently,
  especially after going to the bathroom, after
  changing diapers, and before preparing foods or
  beverages, dispose of soiled diapers properly,
  disinfect diaper changing areas after using them,
  keep children with diarrhea out of child care
  settings, supervise handwashing of toddlers and
  small children after they use the toilet, persons
  with diarrheal illness should not prepare food
  for others.