Widal Test

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

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

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.

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

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.

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

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

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

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

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 .

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

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