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Shigella flexneri

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Title: Shigella flexneri Author: Dave Last modified by: LAP Created Date: 6/28/2003 12:03:16 PM Document presentation format: On-screen Show (4:3) Company – PowerPoint PPT presentation

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Title: Shigella flexneri


1
Shigella flexneri
Simon Flexner
Discoverer of Shigella dysenteriae (1899)
Compiled by Else Marais, Marlene Kassel, Naseema
Aithma, Angela Potgieter Rob Stewart, Branca
Fernandes, and Janet Loakes
2
Gastro-intestinal infections
  • Acute inflammatory enteritis
  • Campylobacter
  • Salmonella
  • Shigella
  • Certain parasites

3
Acute dysentery
  • Frequent small bowel movements
  • Blood and mucous
  • Tenesmus
  • Pain on defecation
  • Inflammatory invasion of intestinal mucosa
  • Bacterial, cytotoxic or parasitic destruction

4
Overview of Shigella species
  • Small, Gram-negative rods
  • Non-motile, non-encapsulated
  • Family Enterobacteriaceae Tribe
    Escherichieae Genus Shigella
  • 40 serotypes, 4 groups
  • A - Shigella dysenteriae
  • B - Shigella flexneri
  • C - Shigella boydii
  • D - Shigella sonnei

5
Overview of Shigella species
  • Sensitive to heat, kill in 55 c in 1 hr
  • S.sonnei survive in soil room temprature for
    9-12 days
  • Survive on fingers for sometime transmit
    through hand contact
  • If suitable,survive in milk other food(15 days
    in sea water)

6
Overview
  • Shigella species
  • 140-200 million people infected annually
  • 650,000 deaths per year,
  • worldwide(esp. developing countries)
  • intracellular pathogens
  • Incubation 6 hrs to 9 days(1-7 days)
  • AB resistance (multiple)
  • 2/3 of all cases and most of deaths in lt 10 y/o
  • Developing countries 1-4 y/o but in
  • epidemics of S. dysenteriae all age group equal

7
Overview
  • In 5-15 of diarrhea 30-50 of dysentry
  • S.flexeneri the most important in endemic
    shigellosis
  • Africa 15 country with outbreak (30 attack rate
    in general population 50 in lt 5 y/o
  • Developed countries children, daycare centers,
    immigrant workers, travelers to developing
  • 2/3 of cases in lt 10 y/o

8
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9
Iran
  • Tehran 52 S.flexeneri, 37 S.sonnei
  • Resistance to ampi, co-trimoxazole, tetra, amoxi,
    chloramphenicole, cephalotin(more in S.flexeneri)
  • The most effective AB is ciprofloxacin then
    ceftizoxime
  • Shiraz 60 S.flexeneri, 28 S.sonnei, 12
    S.boydii, 34 in preschool age
  • Resistance to ampi, co-trimoxazole
  • Sensitive to nalidixic acid, ceftriaxone,
    ceftazidime, ciprofloxacin(100)

10
Descriptive epidemiology
  • Time trend
  • More common in warm seasons
  • Equal in both sexes
  • In temperate climate warm season
  • In tropics rainy season
  • Preschool early school age
  • 1-4 y/o (adult get disease from children)
  • Infants(1- 6 mo) are resistant due to nursing

11
Predisposing factors
  • HIV ( chronic relapsing and causing bateremia
    in spite of AB)
  • Septicemia in Malnutrition, early infancy
    S.dysenteriae type 1
  • EL-Nino phenomenon
  • a dry not rainy winter rainy spring
    increase in dysentery in summer

12
Sensitivity resistance
  • 10-100 micro-organism ingestion in volunteers
    diarrhea in 10-40
  • More virulent in children, malnutrition,
    debilitated old-mostly sub-clinical in adults
  • Oral vaccine some success (short- term)
  • Attenuated oral vaccine prevent clinical dx
  • 2nd attack rate in household contact 40
  • Epidemics in crowding, bad public health( day
    care center, long term care center)

13
Transmission
  • Fecal-Oral(direct or indirect) from patient or
    carrier
  • No handwashing after bowel movement( direct
    contact)
  • Contaminated food( not usual but can cause major
    epidemics)
  • Carrierswithout treatment microorganism shedding
    for 1-4 wks( but the number is low, so
    communicability is lower than pts)
  • Nosocomial infection from pts to healthworkers
    to other pts.
  • Shigella can survive on lab equipments for some
    time
  • Homosexual oral-anal, penile-oral

14
Transmission
  • Contaminated water milk
  • 4-6 wks survive in water( shorter in sun-exposed
    water)
  • Pasteurization eliminate the mo.
  • Insects
  • Fly mechanical, biological
  • Communicable for 4 wks

15
  • Humans and primates only reservoirs
  • Crowded living conditions
  • Poor quality water supplies
  • Inadequate sewage disposal
  • Increase risk of infection

16
Clinical features
  • From asymptomatic to severe (Mortality rates
    vary from 5-10 )
  • Bacilli ingested by epithelial cells of the
    intestinal villi
  • Organisms multiply and spread laterally into
    lamina propria
  • Inflammatory reaction develops with capillary
    thrombosis
  • Necrotic epithelium sloughed leading to
    ulceration
  • Severe cases may become life threatening

17
Clinical features natural history
  • 7-12 bowel movement/day
  • Watery, green or yellow, containing mucous blood
    or undigested food
  • Convulsion, Acute bloody dysentery
  • Fever, malaise, headache, abdominal pain
  • Usually self limited and recovery after 4-7 days,
    sometimes persistent diarrhea
  • HUS
  • Mortality in hospital 20

18
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19
Virulence
  • S.dysenteriae forms potent exotoxin
  • Fluid transuding action as well as
  • Lipo-polysaccharide endotoxin
  • Described as a neurotoxin
  • Toxin levels of S.dysenteriae, highest
  • S.sonnei causes mild illness(short symptomatic
    period and very low mortality)
  • S. flexneri and S.boydii range in severity
  • S.flexneri bacteremia, predisposed by ulcers

20
Virulence
  • Commonly a self-limited disease(mild or mod)
  • 4-7 days(several days to weeks)
  • S.dysenteriae cause more severe disease(20
    mortality in admitted patients)
  • If untreated stool culture for 30 days or more

21
Molecular methods of detection
  • Isolation difficult
  • Genetic probe to the virulence-plasmid developed
    and being tested
  • PCR not routinely done for detection

22
Outbreaks
  • From contaminated water or food
  • contaminated potato salad
  • inadequate toilet facilities
  • Origin of infection- food handler
  • Secondary transmission may occur
  • Flies aid transmission
  • Infants resistant to shigellosis
  • More in formula fed)

23
Patterns of outbreaks
  • Cyclic patterns of 20-30 years
  • From 1900-1925 S.dysenteriae predominated while
    from 1926-1938, S.flexneri was common
  • Currently S.sonnei predominates in Europe and
    USA
  • S.flexneri is predominant in developing
    countries( with boydii dysenteriae)

24
Controlprimary prevention
  • Chlorinated water, waterborne sewage
  • Rigorous hand washing
  • Institutional outbreaks Isolation of the
    infected
  • Infected food handlers - 2 negative cultures
  • Insecticides
  • After P/E of the patient hand washing,
    disinfection of exam. Equipments
  • Vaccination under trial

25
primary prevention
  • Enteric precaution, disinfection of contaminated
    equipment stool( if there is not modern sewage)
  • Infected person withhold from children, other pts
    and food handling 2 consecutive stool culture in
    24 hr interval 48 hr after D/C of AB
  • AB treatment of carriers( without any sign or
    symptoms) not recommended
  • Common writing equipment(pen,)
  • nursing

26
Secondary Prevention
  • Early treatment shorten acute phase of disease
    mo. shedding

27
Treatment
  • Fluid replacement
  • Antimicrobial therapy- reduces duration of
    symptoms
  • Reduces secretion of organisms
  • Adults- oral ciprofloxacin or ofloxacin
  • Children- cotrimoxazole, ampicillin,nalidixic
    acid, ceftriaxone, azithromycin
  • Agents decreasing intestinal motility should not
    be used
  • Untreated lasts 1 day - 1 month (average 7days)
  • Complications - dehydration, seizures,
    septicaemia, pneumonia, keratoconjunctivitis and
    arthritis

28
  • Travellers
  • Eat well cooked food
  • Bottled water
  • Peel all fruit and vegetables
  • Perhaps use prophylactic flouroquinolones
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