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In the tropics malaria is a common disease that causes high fever and other symptoms. By the middle of the 19th century, it was clear that many diseases are caused by microorganisms, and a great many people suspected that malaria was caused by a bacterium. After examining blood from people infected with malaria, Alphonse Laveran in 1889 was able to definitively show that malaria is caused by another type of single-celled organism, a protozoan of the Plasmodium family, which attacks red blood cells. He also identified other single-celled parasites that cause other diseases.