What is the danger of some protozoa for humans? Give examples.

Now in our world there are more than ten thousand of the simplest microorganisms. Some are not dangerous to humans and other animals, but some pose a greater threat to us. They live mainly in water bodies. Therefore, it is often said that it is better not to swim in dubious sources and not to drink unboiled water. These organisms can cause a variety of serious diseases. For example: giardiasis, dysentery, malaria, sleeping sickness, Chagas disease, botulism, staphylococcus aureus and many others. Therefore, you need to follow the rules of hygiene and process water and food before use.