How is protozoa useful to humans?

Protozoa play several beneficial roles for humans, including their use in wastewater treatment, where they help decompose organic matter and reduce pollution. They are also vital in ecological research, serving as indicators of environmental health. Additionally, certain protozoa are used in biotechnology and medical research, contributing to the development of vaccines and treatments for diseases. Lastly, some protozoa are integral to the food chain, supporting the survival of fish and other organisms that humans rely on for food.