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Question #46499
The Question
A 25-year-old patient with a history of TAB vaccination one year ago presents with a mild viral fever. A routine Widal test shows a strong positive result (high titer of O and H agglutinins), but the patient has no active symptoms of enteric fever. Which of the following statements correctly explains this immunological phenomenon and identifies the definitive diagnostic alternative?
Options
- A.
The Widal test detects elevated agglutinins (IgG/IgM) secreted by memory B-cells formed post-vaccination; active infection is best confirmed by PCR detection of the Salmonella genome.
- B.
The TAB vaccine induces persistent cell-mediated immunity, causing T-lymphocytes to agglutinate with Widal reagents; active infection requires confirmation by Widal quantitative titration.
- C.
The Widal test yields a false positive due to the presence of residual live-attenuated vaccine antigens in the blood; active infection must be confirmed by detecting memory B-cells.
- D.
The vaccine suppresses the primary humoral response, causing a delayed hypersensitivity reaction in the Widal test; active infection is confirmed by the Schick test.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Widal Test Specificity|Salmonella typhi|Antibody Structure Logic
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize 'Widal test = Typhoid' from NCERT without understanding that it is an indirect test detecting host antibodies, not the pathogen itself.
The trap exploits the failure to differentiate between the presence of memory B-cell derived antibodies (immunological memory) and active pathogen replication, highlighting why molecular diagnostics (PCR) are superior to serology for definitive confirmation.
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 |