PATHOGENESIS

Shigella cause bacillary dysentery

There are two types of dysentery

They are : a) Amoebic dysentery

b) Bacillary dysentery

AMOEBIC DYSENTERY BACILLARY DYSENTERY

Incubation period is long

Insidious onsetLocal abdominal tenderness

Moderate tenesmus

Fever absent

Short

Sudden onsetGeneralised

severe

present

Stool consists of blood,mucus,necrotic cells&feacal matter

Frequency less

Volume copious

Blood,mucus,hardly any fecal matter

MoreSmall

LAB DIAGNOSISAMOEBIC DYSENTERY BACILLARY

DYSENTERYMICROSCOPYFew pus cellsRBC agglutinated

Trophozoites present

Charcoat layden crystals present

NumerousDiscrete not agglutinated

AbsentAbsent

Bacilli not demonstrated in stool culture

Mild leucocytosis in blood smear

Serum agglutination negative

Can be demonstrated

Marked leukocytosis

positive

Source-infected human beingsMode of transmission

DirectFomitesWaterContaminated foodFliesIn young male homosexuals

Minimum infective dose is low

Pathogenecity resemble that of EIEC

MECHANISM OF ACTION. Bacilli infect the epithelial cells of villi in LI multiplication Inflammatory reaction with capillary thrombosis Necrosis of epithelial cells

Sh.dysenteriae type 1 forms an exotoxin.

CONGO RED BINDING TEST.

VIRULENCE MARKERS ANTIGENS

Virulence test.

CLINICAL MANIFESTATIONS

Incubation period-1 to 7 days.

SYMPTOMSFrequent passage of loose scanty stools containing blood & mucus

Abdominal crampsTenesmusFever & vomiting

In severe cases- bacteremiaCOMPLICATIONS.

ArthritisToxic neuritis ConjunctivitisParotitisHUS

Severity ranges from mild diarrhoea to acute fulminating dysentery

The whole spectrum of infection is termed as SHIGELLOSIS.

Of 10,000 people ingested with Sh.flexneri

25% asymptomatic25% transient fever25%fever with watery diarrhoea25% typical dysentery

EPIDEMIOLOGY

Epidemics always accompanies wars,poverty,lack of sanitation.

Source-humansCasesLess often carriers

ASYLUM DYSENTERY.In USA

North-Sh.sonneiSouth-Sh.flexneri.

In INDIA ,all age groupsFlexneri 50-85%Dysentriae 8-25%Sonnei 2-24% Boydii 0-8%

In recent years,suddenly Sh. Dysentriae became virulent epidemic form.

LAB DIAGNOSIS.

Diagnosis depends on isolating bacilli from feaces.. 1.SPECIMENS.

-fresh stool -rectal swab -ideal specimen -direct swab of an ulcer.

2.TRANSPORT. Sach’s buffered glycerol saline.

3.DIRECT MICROSCOPY.Saline & Iodine preparations.4.CULTURE.MacConkey’s agarDCA

5.COLONY MORPHOLOGY&STAINING

NLFGram negativeMotility6.BIOCHEMICAL REACTIONS.Urease,citrate,H2S,KCN-negative.7.SLIDE AGGLUTINATION

TREATMENT

Uncomplicated shigellosis-self limiting.

Dehydration has to be corrected in infants and children

Antibacterial treatment not indicatedIn severe cases-nalidixic acid,norfloxacin,other flouroquinolones.

PREVENTIONGeneral prophylaxis.Chemoprophylaxis. Immunoprophylaxis.

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