How are protozoa harmful to us?

Explanation

**Step-by-Step Solution:**

1. **Definition of Protozoa**: Protozoa are single-celled organisms that can be found in various environments, including water and soil. Some protozoa are beneficial, but others can be harmful to humans.

2. **Harmful Effects**: Protozoa can become harmful when they act as parasites. A parasite is an organism that lives on or in a host organism and gets its food at the expense of its host, which can lead to various health issues.

3. **Examples of Harmful Protozoa**:
- **Trypanosoma**: This protozoan is responsible for causing sleeping sickness in humans. It is transmitted by the bite of the tsetse fly and can lead to severe neurological problems if not treated.
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