Typhoid fever

 Pathogenesis of typhoid fever:

[A]Causative agent:Salmonella typhi.

[B]Route of transmission: Faeco-oral route(from food,water,ice cream etc)

[C]Incubation period:10-14 days.

Pathogenesis:

Entry of salmonella typhi to the stomach.

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Duodenum(Small intestine)

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Mesentric lymph nodse (Multiply)Via thoracic duct.

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Enter blood (Primary bacteraemia)

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Multiply in liver,spleen,bone marrow,kidney,lung.

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Pass into blood causing secondary baxtermia(Onset of fever & other signs of clinical illness-Typhoid fever)

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Gall bladder,liver,spleen(2nd & 3ed week)

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Peyer’s patches of intestine.

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Lymphatics follicles(Necrosis & Sloughing).

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Typhoid fever/Ulcer(4th & 5th weeks)

Lab diagnosis of Typhoid fever:                       

[A]Principle:Diagnosis is based on isolation of salmonella typhi by blood culture and antigen.Perference of diagnosis defer according to duration of fever.

[B]Steps:

(A)Specimen collection:

a)      Blood:For culture (1st week).

b)     Serum:For widal test (2nd week).

c)      Stool:For culture (2nd & 3rd week).

d)     Urine:For urine culture (4th week).

(B)Microscopic examination:It is not helpful.

a)      WBC count may be normal or low.

b)     Raised ESR.

(C)Isolation & Identification(Culture):

Blood culture:Mostly reliable in 1st week can be done in 3 processess:

a)      Rapid culture system(Examined after 24 hours).

b)     Trypticase soy broth(Blood is collected before starting specific antibiotic).

c)      Automated method(Solid media are used very rapid with in 6 hour)

Stool culture:Positive for 2nd or 3rd week.It is done in at least 2 solid media (e.g Macconkey agar deoxycholate citrate agar etc) and 1 liquid media (e.g Tetrathionate broth).

Urine culture:Positive in 2nd,3rd & 4th week,culture is done   in- Macconkey agar deoxycholate citrate agar.

Serological test:Positive from 2nd week widle test usually positive.