Protozoan diseases are illnesses caused by single-celled organisms known as protozoa. These microscopic creatures can infect humans and animals, leading to various health issues. Common protozoan diseases include malaria, caused by the Plasmodium parasite, and amoebic dysentery, caused by Entamoeba histolytica. Transmission often occurs through contaminated water, food, or insect bites. Symptoms can range from mild gastrointestinal distress to severe fever and fatigue. Preventive measures include maintaining good hygiene, using insect repellent, and ensuring safe drinking water to reduce the risk of infection from these harmful organisms.