Transcript 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
Gastro-intestinal infections
Acute inflammatory enteritis:
•
Campylobacter
•
Salmonella
• Shigella
•
Certain parasites
Acute dysentery
• Frequent small bowel movements
• Blood and mucous
• Tenesmus
• Pain on defecation
• Inflammatory invasion of intestinal mucosa
• Bacterial, cytotoxic or parasitic destruction
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
Overview of Shigella species
• Sensitive to heat, kill in 55 c in 1 hr
• S.sonnei survive in soil & room temprature for 912 days
• Survive on fingers for sometime & transmit
through hand contact
• If suitable,survive in milk & other food(15 days in
sea water)
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 < 10 y/o
•Developing countries: 1-4 y/o but in
epidemics of S. dysenteriae all age group equal
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 < 5 y/o
• Developed countries: children, daycare centers,
immigrant workers, travelers to developing
• 2/3 of cases in < 10 y/o
‫بروز در سال ‪ 11/8 :1383‬در ‪ 100‬هزار نفر‬
‫سيستان و بلوچستان(‪)63‬‬
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%)
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
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
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…)
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)
– Carriers:without 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
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
• Humans and primates: only reservoirs
• Crowded living conditions
• Poor quality water supplies
• Inadequate sewage disposal
• Increase risk of infection
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
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%
‫• تعريف اپيدميولوژيك ندارد‪.‬‬
‫• گزارش غير فوري‬
‫• در صورت بروز همه گيري گزارش فوري‬
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
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
Molecular methods of detection
• Isolation difficult
• Genetic probe to the virulence-plasmid developed and being
tested
• PCR not routinely done for detection
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)
Patterns of outbreaks
• Cyclic patterns of 20-30 years
• From 1900-1925 S.dysenteriae predominated while from 19261938, S.flexneri was common
• Currently S.sonnei predominates in Europe and USA
• S.flexneri is predominant in developing countries( with boydii
& dysenteriae)
Control
primary 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
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
Secondary Prevention
• Early treatment shorten acute phase of
disease & mo. shedding
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
• Travellers:
Eat well cooked food
Bottled water
Peel all fruit and vegetables
Perhaps use prophylactic flouroquinolones