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.
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.
Charles Louis Alphonse Laveran