A biological agent is a microorganism, such as a bacterium, virus, or fungus, that can cause disease in humans, animals, or plants. These agents can be naturally occurring or engineered for research and medical purposes. They are often studied in laboratories to understand their effects and develop treatments or vaccines. Biological agents can be used in various fields, including medicine, agriculture, and biotechnology. In medicine, they help in creating vaccines to prevent diseases. In agriculture, they can be used to control pests or enhance crop growth. However, some biological agents can also pose risks if misused.