One of the following diseases is not a sexually transmitted disease

Options

A. 1)Trichomoniasis
B. 2)Chlamydiasis
C. 3)Encephalitis
D. 4)Syphilis

Answer

To determine which of the following diseases is not a sexually transmitted disease (STD), we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understand the Definition of STD:**
- Sexually transmitted diseases (STDs), also known as sexually transmitted infections (STIs), are infections that are primarily spread through sexual contact.

2. **Analyze Each Option:**
- **Option 1: Trichomoniasis**
- Trichomoniasis is caused by a protozoan parasite called *Trichomonas vaginalis*. It is a common STD.
- **Conclusion:** This option is incorrect as it is an STD.

- **Option 2: Chlamydia**
- Chlamydia is caused by the bacterium *Chlamydia trachomatis*. It is also a common sexually transmitted infection.
- **Conclusion:** This option is incorrect as it is an STD.

- **Option 3: Encephalitis**
- Encephalitis is an inflammatory disease of the brain that can be caused by various pathogens, including viruses and bacteria. It is not primarily transmitted through sexual contact.
- **Conclusion:** This option is correct as it is NOT an STD.

- **Option 4: Syphilis**
- Syphilis is caused by the bacterium *Treponema pallidum* and is a well-known sexually transmitted disease.
- **Conclusion:** This option is incorrect as it is an STD.

3. **Final Answer:**
- The disease that is not a sexually transmitted disease is **Option 3: Encephalitis**.