In 1850, Davaine along with French dermatologist Pierre François Olive Rayer (1793-1867) discovered a certain microorganism in the blood of diseased and dying sheep. In the diseased blood, Rayer and Davaine isolated the bacillus which is known as Bacillus anthracis, the causative bacterium of anthrax. Soon afterwards, Rayer published an essay on anthrax, which contained the first description of Bacillus anthracis.
In 1863 Davaine demonstrated that the anthrax bacillus could be directly transmitted from one animal to another. He was able to identify the causative organism but unable to solve what created it. That was left to the German physician Robert Koch, who discovered the responsible pathogen.
Casimir Davaine is also credited for pioneer work in the study of septicemia (blood poisoning).