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Question #46502
The Question
A patient presenting with sustained high fever (39°C to 40°C), weakness, and intestinal complications tests negative for Salmonella typhi using the standard Widal test. However, a subsequent ELISA confirms the infection. Based on the principles of diagnostic biotechnology, which of the following best explains this discrepancy?
Options
- A.
The pathogen underwent phase variation of its flagellar H-antigen, evading the standard agglutination antibodies of the Widal test, whereas ELISA utilized monoclonal antibodies against a conserved epitope.
- B.
The Widal test utilizes highly specific monoclonal antibodies that failed due to phenotypic switching, whereas ELISA relies on polyclonal serum to achieve whole-cell agglutination.
- C.
The pathogen's somatic O-antigen underwent a conformational change, preventing the enzyme-substrate complex formation required for a positive Widal test.
- D.
The Widal test relies on the detection of early IgM antibodies against the pathogen's endotoxin, whereas ELISA directly amplifies the pathogen's surface antigens using Taq polymerase.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Widal Test Specificity|ELISA Logic|Antibody Structure Logic
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often rote-memorize 'Widal = Typhoid' (NCERT Human Health) and 'ELISA = Antigen-Antibody interaction' (NCERT Biotech) without synthesizing their mechanical differences.
The trap lies in functional confusion—distractors falsely assign enzyme-substrate reactions to Widal, agglutination to ELISA, or amplification to ELISA.
Recognizing that Widal's reliance on whole-cell agglutination makes it vulnerable to antigenic phase variation bridges basic immunology with advanced diagnostic pathology.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Human Health and Disease - Class 12 |
| Concept | Widal Test Specificity |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |