Laboratory diagnosis€¦Laboratory diagnosis Stool RE Macroscopic examination color, form and...
Transcript of Laboratory diagnosis€¦Laboratory diagnosis Stool RE Macroscopic examination color, form and...
Laboratory diagnosis
Specimens
Fresh stool, mucus flecks and rectal swabs for culture
Serum specimens, if desired, must be taken 10 days apart to demonstrate a rise in titer of agglutinating antibodies
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Laboratory diagnosis
Stool RE
Macroscopic examination
color, form and consistency
only blood and mucous present
no faecal matter (red currant jelly stool)
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Laboratory diagnosis
Stool RE
Microscopic examination
Large numbers of fecal leukocytes and somered blood cells often are seen microscopically
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Culture
Specimens are inoculated onto
nutrient agar,
blood agar
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Laboratory diagnosis
Culture
Differential media
MacConkey agar
EMB agar
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Laboratory diagnosis
Culture
Selective media
Hektoen enteric agar or SalmonellaShigella agar), which suppress other Enterobacteriaceae and gram positive organisms
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Laboratory diagnosis
Culture
Colourless (lactosenegative) colonies are inoculated into TSI agar
Organisms that fail to produce H2S, that produce acid but not gas in the butt and an alkaline slant in TSI agar medium
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Laboratory diagnosis
Culture
Colonies that are nonmotile should be subjected to slide agglutination by specific Shigella antisera
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Laboratory diagnosis
Identification
Gram stain smear shows gram negative bacilli
Motility test shows nonmotile bacilli
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Laboratory diagnosis
Sugar fermentation test
Lactose, Glucose, Mannitol, Sucrose
Other biochemical tests
IMViC U
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Laboratory diagnosis
1 2
K
N
K
Agas
H2S
A
A
K
A
Triple Sugar Iron agar slant (TSI slant)
Shigella A = acidicK = alkalineN = neutral
Voges-Proskauer testpositivenegative
Voges-Proskauer test negative
Urease test
positivenegative
urease test negative
Citrate utilization test
positivenegative
no citrate utilization
Serological identification
Slide agglutination by specific shigella antisera (against S. dysenteriae, S. flexneri, S. boydii, S. sonnei)
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Laboratory diagnosis
Serology (Antibody detection)
Serology is not used to diagnose shigella infections
Shiga toxin can be tested for by Vera and HeLa cell tests
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Laboratory diagnosis
Molecular methods
PCR targeting
1 . Invasion plasmid antigen H (ipaH)
2 .Gene for Shigella enterotoxin 2 (ShET2 )
3 .Gene encoding aerobactinmediated iron uptake system
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Laboratory diagnosis
Molecular methods
Typing
Plasmid profile
Colicine typing
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Laboratory diagnosis
Character Bacillary dysentery
Amoebic dysentery
Incubation period
Short (<7 days) Long
Onset Acute Insidious
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Laboratory diagnosis
• Symptoms
• Bacillary dysentery
• Amoebic dysentery
• Tenesmus
• Generalized abdominal tenderness
Severe
• Localized over sigmoid,
caecum, colon).
Moderate
• Stool • mucus and blood
• Feces, mucusand blood
• Volume • small • Copious
Laboratory diagnosis
• Microscopic examination
• Bacillary dysentery
• Amoebic dysentery
• RBC • discreate • clumps
• Pus cells • numerous • few
• Eosinophils • (-) • (+)• Charcott
leyden crystal • (-) • (+)
Laboratory diagnosis
Character Bacillary Dysentery Amoebic Dysentery
incubation periodonset SymptomsTenesmus StoolVolume Microscopic examination: RBC pus cells, Eosinophils Charcott leyden crystal
Short (<7 days)Acute Generalized abdominal tenderness Severemucus and bloodsmall discreatenumerous()()
LongInsidious Localized over sigmoid, caecum, colon). ModerateFeces, mucus and bloodCopious ClumpsFew(+)(+)
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Laboratory diagnosis
Infection is followed by a typespecific antibody response
Serum antibodies fails to protect against infection
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Immunity
IgA antibodies in the gut may be important inlimiting reinfection
Live attenuated strains given orally as experimental vaccines
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Immunity
Treatment
Ciprofloxacin, ampicillin, doxycycline, and trimethoprimsulfamethoxazole
suppress acute clinical attacks of
dysentery
shorten the duration of symptoms
fail to eradicate the organisms from
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Treatment
Multiple drug resistance can be transmitted by plasmids and resistant infections are widespread
Many cases are selflimited
Opioids should be avoided in Shigella dysentery
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Epidemiology
Shigellae are transmitted persontoperson
Most cases of shigella infection (S. dysenteriae can spread widely
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Epidemiology
Epidemic outbreaks of disease occur in daycare centers, nurseries and custodial institutions
Disease occurs worldwide with no seasonal incidence (consistent with persontoperson spread involving a low inoculum)
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Epidemiology
S. sonnei the U.S. infections
S. flexneri predominates in developing countries
Epidemics of S. dysenteriae occur in Africa and Central America, with case fatality rates of 5% to 15%
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Epidemiology
Highest risk for disease
young children in daycare centers, nurseries and custodial institutions
siblings and parents of these children
male homosexuals
60% of all infections occur in children under 10 years of age
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Prevention and control
Mass chemoprophylaxis for limited periods of time (e.g. in military personnel) has been tried
Resistant strains of shigellae tend to emerge rapidly
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Prevention and control
General measures
Sanitary control of water, food and milk
sewage disposal
Fly control
Isolation of patients and disinfection of excreta
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Prevention and control
General measures
Detection of subclinical cases and carriers, particularly food handlers
Antibiotic treatment of infected individuals
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Prevention and control
Specific measures
Vaccines
Live attenuated strains rational attenuation
Oral route » mucosal vaccine »
One dose, Induction of antiLPS SIgA
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Subunit vaccines
Based on the use of detoxified LPS
Systemic route (IM, SC)
Induction of anti LPS IgG
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Prevention and control
Subunit vaccines
*Efficient in young children
*Pentavalent
S.dysenteriae 1, S.sonnei,
S.flexneri 2a, S.flexneri 3a, S.flexneri 6
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Prevention and control
Vaccine: SC602
A Shigella flexneri 2a specifically attenuated specifically attenuated vaccine strain
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Prevention and control
KLEBSIELLA PNEUMONIA
RHINOSCLEROMA