WIDAL test is used for the detection of

Options

A. Disease caused by a protozoan called Trichomonas
B. Disease caused by a rod shaped bacterium called Salmonella typhi
C. Disease caused by a spherical bacterium called N. gonorrhoea.
D. Disease caused by a spiral bacterium called Treponema pallidum

Answer

### Step-by-Step Solution:

1. **Understanding the Widal Test**: The Widal test is a serological test used to detect the presence of specific antibodies in the serum of a patient. It is primarily used to diagnose infections caused by certain bacteria.

2. **Identifying the Target Bacteria**: The Widal test is specifically used for the diagnosis of enteric fever, commonly known as typhoid fever. This disease is caused by the bacterium Salmonella typhi.

3. **Analyzing the Options**:
- **Option A**: Disease caused by a protozoan called Trichomonas - This refers to trichomoniasis, which is incorrect.
- **Option B**: Disease caused by a rod-shaped bacterium called Salmonella typhi - This is correct as it relates to typhoid fever.
- **Option C**: Disease caused by a spherical bacterium called Neisseria gonorrhea - This refers to gonorrhea, which is also incorrect.
- **Option D**: Disease caused by a spiral bacterium called Treponema pallidum - This refers to syphilis, which is also incorrect.

4. **Conclusion**: Based on the analysis of the options, the Widal test is used for the detection of typhoid fever, which is caused by the rod-shaped bacterium Salmonella typhi. Therefore, the correct answer is **Option B**.