Infection by a pathogen can be detected by the presence of antigens or by detecting the antibody synthesized against the pathogen. The test/s based on this principle is/are

Options

A. PCR
B. ELISA
C. Both PCR and ELISA
D. Neither PCR nor ELISA

Answer

To solve the question regarding the detection of infection by a pathogen through the presence of antigens or antibodies, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question states that infection by a pathogen can be detected either by the presence of antigens or by the antibodies synthesized against the pathogen. We need to identify the tests that are based on this principle.

2. **Identifying the Tests**: The options provided are:
- A) PCR (Polymerase Chain Reaction)
- B) ELISA (Enzyme-Linked Immunosorbent Assay)
- C) Both PCR and ELISA
- D) Neither PCR nor ELISA

3. **Analyzing PCR**: PCR is a molecular biology technique used to amplify DNA sequences. It is primarily used for detecting the genetic material of pathogens, not for detecting antigens or antibodies. Therefore, PCR does not fit the criteria mentioned in the question.

4. **Analyzing ELISA**: ELISA is a widely used laboratory test that detects the presence of antibodies or antigens in a sample. It operates on the principle of antigen-antibody interaction, where an antigen is immobilized on a solid surface, and a sample containing antibodies is added. If antibodies specific to the antigen are present, they will bind, and a secondary enzyme-linked antibody will produce a measurable signal (usually a color change) upon substrate addition.

5. **Conclusion**: Since ELISA specifically detects the presence of antibodies against pathogens or the antigens themselves, it directly aligns with the question's criteria. Therefore, the correct answer is **B) ELISA**.

### Final Answer:
**B) ELISA**

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