Which one of the following pairs of diseases is viral as well as transmitted by mosquitoes ?

Options

A. Encephalitis and sleeping sickness
B. Yellow fever and sleeping sickness
C. Elephantiasis and dengue
D. Yellow fever and dengue

Explanation

To solve the question "Which one of the following pairs of diseases is viral as well as transmitted by mosquitoes?", we will analyze each option provided.

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify a pair of diseases that are both viral and transmitted by mosquitoes.

2. **Evaluate Each Option**:
- **Option 1: Encephalitis and Sleeping Sickness**
- Encephalitis can be viral and transmitted by mosquitoes (e.g., West Nile virus).
- Sleeping sickness, however, is caused by a parasite (Trypanosoma) and transmitted by tsetse flies, not mosquitoes.
- **Conclusion**: This option is incorrect.

- **Option 2: Yellow Fever and Sleeping Sickness**
- Yellow fever is a viral disease transmitted by mosquitoes (specifically, Aedes aegypti).
- Sleeping sickness, as mentioned earlier, is not viral and is not transmitted by mosquitoes.
- **Conclusion**: This option is incorrect.

- **Option 3: Elephantiasis and Ending**
- Elephantiasis is caused by parasitic filarial worms (not viral) and transmitted by mosquitoes.
- The term "ending" is unclear and does not refer to a known disease.
- **Conclusion**: This option is incorrect.

- **Option 4: Yellow Fever and Dengue**
- Yellow fever is a viral disease caused by the Flavivirus and transmitted by mosquitoes.
- Dengue is also a viral disease caused by the Dengue virus (a type of Flavivirus) and is transmitted by the same mosquito vector, Aedes aegypti.
- **Conclusion**: This option is correct.

3. **Final Answer**: The correct pair of diseases that are both viral and transmitted by mosquitoes is **Option 4: Yellow Fever and Dengue**.