Pathogenic protozoa are single-celled organisms that can cause diseases in humans and animals. They are often transmitted through contaminated water, food, or insect bites. Common examples include Plasmodium, which causes malaria, and Entamoeba histolytica, responsible for amoebic dysentery. These microorganisms can invade host tissues and disrupt normal bodily functions, leading to various health issues. Symptoms of infections may range from mild gastrointestinal disturbances to severe systemic illnesses. Effective prevention includes proper sanitation, safe food handling, and vector control to reduce the risk of transmission.