Pathogenesis of enteric fever

Pathogenesis of enteric fever

Causative agent:

Salmonella (at least 10⁶   -10⁹ microorganism are needed to cause disease)

Route of entry: Faeco –oral route.

Incubation period: 10-14 days.

Pathogenesis of enteric fever:

Entry of salmonella to the stomach

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Duodenum (small intestine)Multiply in mononuclear phagocytes of payer’ s  patches

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Intestine

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Mesenteric lymph nodes

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Enter blood (primary bacteraemia)

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Liver ,spleen ,bone marrow ,kidney ,lung,

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Secondary heavy bacteraemia [onset of clinical illness-enteric fever]

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Gall bladder, liver & spleen [2^nd & 3^rd weeks]

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Peyer’s patches of intestine.

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Lymphatic follicles

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Typhoid ulcer[4^th &5^th weeks]

Laboratory diagnosis of enteric fever:

Diagnosis is based on isolation of salmonella species by blood culture. Blood culture and antigen detection is reliable in the 1^st week.

Steps:

1. Specimen collection:

ð  Blood for blood culture-1^st &2^nd week.

ð  Serum for widal test-2^nd week.

ð  Stool for stool culture-3^rd week.

ð  Urine for urine culture -4^th week.

2. Microscopic examination:

ð  It is not helpful.

3. Isolation % identification from culture.

Blood culture:

Positive in 1^st week of infection. Can be done in 3 processes-

(a)    Traditional-(using liquid media on biphasic media)

(b)   Lytic method –(After processing in lytic solution in solid media)

(c)    Automated-(very rapid –within 6 hour)

Stool culture:

Positive in 2^nd or 3^rd week . It is done in-

ð  Mac-Conkey’s agar.

ð  Deoxucholate citrate agar (DCA)

4. Serological test:

Positive in 2^nd week.

->Widal test.