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W.B.C.S. Examination Notes On – Widal Test – Medical Science Notes.
Widal test is an agglutination test which detects the presence of antibodies in patient’s serum produced against the causative agents of enteric fever (Salmonella Typhi and Salmonella Paratyphi A, B and C).Continue Reading W.B.C.S. Examination Notes On – Widal Test – Medical Science Notes.
It is one of the common methods employed for serological diagnosis of typhoid and paratyphoid fever especially in the endemic regions.
The test was developed by Greembaum and Georges Ferdinand Widal in 1896 for diagnosis of enteric fever in humans.
The Widal test utilizes antigen-antibody interactions to detect specific antibodies in the serum sample of typhoid patients. The antigens used are derived from the bacterial cells of Salmonella Typhi and Salmonella Paratyphi.
Salmonella Typhi possesses O antigen on the cell wall and H antigen on flagella. Similarly, Salmonella Paratyphi A and Salmonella Paratyphi B also possess O antigen on their cell wall and but have AH and BH antigen on their flagella respectively.
On infection, these antigens stimulate the body to produce specific antibodies which are released in the blood. These specific antibodies against the antigens can be detected in the patient’s serum after 6 days of infection (fever).
Objective of Widal Test
The test is performed to detect serum antibodies against Salmonella Typhi and Salmonella Paratyphi aiding in diagnosis of enteric fever in suspected patients.
Principle of Widal Test
Individual infected with Salmonella Typhi or S. paratyphi produce antibodies against either somatic (O) antigens and/or flagellar antigens (H). These produced antibodies in serum, if exposed to bacterial suspension carrying homologous antigens, result in agglutination. The agglutination reaction can be seen as visible clumping.
In the test, the patient’s serum is mixed with killed bacterial suspension of Salmonella carrying specific O, H, AH and BH antigens and observed for agglutination reaction. If the patient’s serum contains specific antibodies against the antigens, clumping is evident which indicates positive test. Absence of agglutination indicates a negative result.
Requirements for Widal Test
Fresh serum, kit containing Salmonella antigen (O, H, AH and BH antigens), positive control, Widal test card or slide, Applicator stick.
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