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.
Entry of salmonella typhi to the stomach.
Mesentric lymph nodse (Multiply)Via thoracic duct.
Enter blood (Primary bacteraemia)
Multiply in liver,spleen,bone marrow,kidney,lung.
Pass into blood causing secondary baxtermia(Onset of fever & other signs of clinical illness-Typhoid fever)
Gall bladder,liver,spleen(2nd & 3ed week)
Peyer’s patches of intestine.
Lymphatics follicles(Necrosis & Sloughing).
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.
- 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.