Passage: In 1880, while working in the military hospital in Constantine, Algeria, he discovered that the cause of malaria is a protozoan, after observing the parasites in a blood smear taken from a patient who had just died of malaria.  He found the causative organism to be a protozoan which he named Oscillaria malariae, but later renamed Plasmodium. This was the first time that protozoans were shown to be a cause of disease of any kind. The discovery was therefore a validation of the germ theory of diseases.Laveran later worked on the trypanosomes, particularly sleeping sickness, and showed once again that protozoans were responsible for the disease.

Question: What was found to be causing Malaria?
protozoan