1. Widal Test

2. Widal test is a serological test for diagnosis of Typhoid ( Enteric) fever
Typhoid (Enteric) fever is caused by genus Salmonella

3. Salmonella are gram negative, peritrichous rod shaped bacilli
(Image from the Centers for Disease Control and Prevention.)

4. Normal habitat
S. typhi and S. paratyphi are only found in humans and excreted in the feces and urine of infected patients and are present in the gall bladder of long term carriers.
Infection is by the ingestion of the organism in food/water or from contaminated hands.
S. typhi is mainly spread by water and S. paratyphi by food.

5. Pathogenecity S. Typhi causes : S. Paratyphi A & B causes:
Typhoid fever. Symptoms include: fever, headache, splenomegaly and mental confusion, rashes [rose spots].
S. Paratyphi A & B causes:
Paratyphoid or enteric fever which is milder than typhoid fever.
S. Paratyphi C causes:
Mainly cause septicemia

6. Salmonella Antigens O Antigens H Antigens Vi Antigens
Cell wall heat stable antigens.
Groups are designed A- Z,
Medically important belong to groups A to G.
H Antigens
Flagella, heat-stable antigens
Serotyped by their H antigens
Vi Antigens
Surface or capsule (K) antigen can be found in S. typhi, S. paratyphi C and a few other Salmonella.

7. Antibody appearance
Anti-O antibody appears 8 days after the onset of disease & mainly of IgM
Anti-H antibody appears 12 days after the beginning of disease & mainly of IgG
Anti-Vi appears in 21 days
Anti-O antibody disappear 3-6 monthes by treatment, but Anti-H may remind more

8. Widal Test
This tests is used for detection of antibodies to O & H Ag of:
S. typhi (group D)
S. paratyphi A
S. paratyphi B

9. Serotype O H S. Typhi (group D) S. paratyphi A S. paratyphi B D d A a

10. Widal test Slide method: 80μl, 40μl, 20μl, 10μl & 5μl Tube method:
The same as Wright

11. Causes Of False-positive Widal Tests
Previous immunization with Salmonella antigen.
Cross-reaction with non – typhoidal Salmonella.
Variability and poorly standardized commercial antigen preparation.
Infection with malaria
Other Enterobacteriaceae charring the same s-LPS .

12. Widal interpretation
A 2-4 four fold rise in titer from the serum tested during the first week and the 2-4 week very significant
High titer > 1:160 against O antigen suggest infection
High titer > 1:160 against H antigen suggest past infection

13. Widal interpretation
Active typhoid: if titers were above 1:160 against O & 1:80 against H or more
In acute infection, O antibody appears first * after recovery decline & in 3-6 months disappears.
H antibody appears slightly later but persists longer and can be used to distinguish between various types of enteric fever.
rising progressively, later falling, and often disappearing within a few months