Agents spreading diseases are

Options

A. malaria
B. Kala azar
C. filaria
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Disease Agents**:
- Diseases are caused by various agents that can spread infections. These agents include bacteria, viruses, fungi, protozoa, and helminths (worms).

2. **Identifying Examples**:
- For instance, malaria is caused by the protozoan parasite *Plasmodium*, which is transmitted by the female Anopheles mosquito.
- Another example is black fever, which is caused by the protozoan *Leishmania*, specifically *Leishmania donovani*.
- Lastly, filariasis is caused by parasitic worms, specifically *Wuchereria bancrofti*.

3. **Categorizing the Agents**:
- The agents can be categorized as:
- **Bacteria**: Single-celled organisms that can cause diseases like tuberculosis.
- **Viruses**: Smaller than bacteria, they require a host to replicate and can cause diseases like influenza.
- **Fungi**: Can cause infections like athlete's foot or ringworm.
- **Protozoa**: Single-celled organisms that can cause diseases like malaria and amoebic dysentery.
- **Helminths**: Multicellular organisms (worms) that can cause diseases like filariasis.

4. **Conclusion**:
- Based on the examples and categories discussed, the agents spreading diseases include all the mentioned types: bacteria, viruses, fungi, protozoa, and helminths.

5. **Final Answer**:
- Therefore, the answer to the question "Agents spreading diseases are" is **"All of these"**, as all the mentioned agents can cause diseases.