In 1883, he presented a doctoral dissertation in medicine titled "Des Nouvelles Acquisitions sur la Rage", in which he described his research on rabies with Pasteur since 1881, which led to the development of the first vaccination against this fearsome disease. Roux discovered the idea of intracranial transmission of rabies, which paved the road for many more Pastorian milestones in research. Roux was now recognized as an expert in the nascent sciences of medical microbiology and immunology. With Pasteur's other assistants (Edmond Nocard, Louis Thuillier, who died while in Alexandria after contracting the disease, and Straus), Roux traveled in 1883 to Egypt to study a human cholera outbreak there, but they were unable to find the pathogen for the disease, which was later discovered in Alexandria by the German physician Robert Koch (1843–1910).