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PATHOGENESIS

PATHOGENESIS

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PATHOGENESIS

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  1. PATHOGENESIS

  2. Shigella cause bacillary dysentery • There are two types of dysentery • They are : a) Amoebic dysentery • b) Bacillary dysentery

  3. AMOEBIC DYSENTERY BACILLARY DYSENTERY • Incubation period is long • Insidious onset • Local abdominal tenderness • Moderate tenesmus • Fever absent • Short • Sudden onset • Generalised • severe • present

  4. Stool consists of blood,mucus,necroticcells&feacal matter • Frequency less • Volume copious • Blood,mucus,hardly any fecal matter • More • Small

  5. LAB DIAGNOSIS AMOEBIC DYSENTERY BACILLARY DYSENTERY • MICROSCOPY • Few pus cells • RBC agglutinated • Trophozoites present • Charcoatlayden crystals present • Numerous • Discrete not agglutinated • Absent • Absent

  6. Bacilli not demonstrated in stool culture • Mild leucocytosis in blood smear • Serum agglutination negative • Can be demonstrated • Marked leukocytosis • positive

  7. Source-infected human beings • Mode of transmission • Direct • Fomites • Water • Contaminated food • Flies • In young male homosexuals

  8. Minimum infective dose is low • Pathogenecity resemble that of EIEC

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

  10. Sh.dysenteriae type 1 forms an exotoxin. • CONGO RED BINDING TEST. • VIRULENCE MARKERS ANTIGENS • Virulence test.

  11. CLINICAL MANIFESTATIONS

  12. Incubation period-1 to 7 days. • SYMPTOMS • Frequent passage of loose scanty stools containing blood & mucus • Abdominal cramps • Tenesmus • Fever & vomiting

  13. In severe cases- bacteremia • COMPLICATIONS. • Arthritis • Toxic neuritis • Conjunctivitis • Parotitis • HUS

  14. 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% asymptomatic • 25% transient fever • 25%fever with watery diarrhoea • 25% typical dysentery

  15. EPIDEMIOLOGY

  16. Epidemics always accompanies wars,poverty,lack of sanitation. • Source-humans • Cases • Less often carriers

  17. ASYLUM DYSENTERY. • In USA • North-Sh.sonnei • South-Sh.flexneri.

  18. In INDIA ,all age groups • Flexneri 50-85% • Dysentriae 8-25% • Sonnei 2-24% • Boydii 0-8%

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

  20. LAB DIAGNOSIS.

  21. Diagnosis depends on isolating bacilli from feaces.. 1.SPECIMENS. -fresh stool -rectal swab -ideal specimen -direct swab of an ulcer.

  22. 2.TRANSPORT. • Sach’s buffered glycerol saline. 3.DIRECT MICROSCOPY. • Saline & Iodine preparations. 4.CULTURE. • MacConkey’s agar • DCA

  23. 5.COLONY MORPHOLOGY&STAINING • NLF • Gram negative • Motility 6.BIOCHEMICAL REACTIONS. • Urease,citrate,H2S,KCN-negative. 7.SLIDE AGGLUTINATION

  24. TREATMENT

  25. Uncomplicated shigellosis-self limiting. • Dehydration has to be corrected in infants and children • Antibacterial treatment not indicated • In severe cases-nalidixicacid,norfloxacin,otherflouroquinolones.

  26. PREVENTION • General prophylaxis. • Chemoprophylaxis. • Immunoprophylaxis.

  27. Thank you