During the following years, Laveran continued his work in Algeria. He also visited Italy in 1882, where he looked for the parasite in the air, the water, and the soil of marshlands. That search proved negative, making him suspect that the parasite could be in the body of mosquitoes, which were abundant in that environment. He put forward this hypothesis in his "Treatise on Marsh Fevers" of 1884 and defended it at the International Congress of Hygiene in Budapest (1894). In his 1891 treatise "On Malaria And Its Hematozoon," he wrote, without giving a reference, that "King, in America, had the idea that mosquitoes played a role in malaria."
Laveran’s publications were generally met with skepticism, especially among the Italians and the disciples of Louis Pasteur (except Elie Metchnikoff), who were in favor of a bacterial cause. Later, following his return in 1884 to the Val-de-Grâce School of Military Medicine, Laveran invited Pasteur to visit and see under his microscope the motile, flagellated bodies. Pasteur was immediately convinced (Roux, 1915). It was not until the years 1885-1890 that the parasitic origin of malaria was accepted.