Charles Louis Alphonse Laveran

Laveran had first encounter with malarial parasites while working at Constantine. Malaria was till then considered as a miasmatic disease, a sort of mystical airborne infection.[8] From the blood samples of malarial individuals, Laveran observed pigmented cells (later known as haemozoin[9] which indicate infection of red blood cells with malarial parasite). He knew[10] that German physician Rudolf Virchow had described the malarial pigment in 1849.[11][12] Virchow had seen from a person who died of malaria several pigmented cells in the blood showed for the first time the link between blood infection and malaria.[13] However, he mistakenly identified the pigmented cells as those of endothelial cells from the spleen and white blood cells.[14] Malarial infection therefore erroneously known as pigmented white blood cells (melaniferous leucocytes).[15] Laveran was the first to think of such infected blood cells were by parasites, but his interest in the issue was ended by his transfer to non-malarial station.[4]

Soon after he returned to the military hospital in Constantine, Algeria, in 1880, Laveran discovered the cause of malaria as a protozoan, after observing the parasites in a blood smear taken from a person who had just died of malaria.[16] On 20 October, he first noticed the parasite in various forms and described it with, as later remarked, "accurate"[17] and "excellent freehand drawings."[6] His initial hunch that pigmented cells in malaria were due to parasitic infection became obvious as he observed not only pigmented cells, but also several cells with filaments that were moving about. He continued to investigate other cases of malaria and reported his discoveries on 24 December to the Société médicale des hôpitaux de Paris. He described three unique biological characters of malarial parasite: crescent or oval bodies that were transparent and had rounded pigment granules at the centre, spherical bodies that possessed three to four filaments capable of worm-like movements, and smaller spherical bodies that had small granules and lacked filaments.[18] The crescent or oval cells are now known as the gametocytes, filamented bodies as exflagellation (male gemete), and small spherical bodies as trophozoites.[19]

Laveran's report was published in 1881 in the Bulletins et Mémoires de la Société médicale des hôpitaux de Paris, and in English in The Lancet.[8][20] He wrote:

On the 20th October last, while examining by microscope the blood of a patient suffering from malarial fever I observed in the midst of the red blood corpuscles the presence of elements which appeared to me to be of parasitic origin. Since then I have examined 44 cases, and in 26 have found the same elements. I have searched in vain for these elements in the blood of patients suffering from diseases other than malaria.[18]

The same year he published a 104-paged monograph Nature parasitaire des accidents de l'impaludisme: description d’un nouveau parasite trouvé dans le sang des malades atteints de fièvre palustre (Parasitic Nature of Malarial Disease: Description of a New Parasite Found in the Blood of Patients with Malarial Fever).[21] In it, he named the parasite Oscillaria malariae[22] (which after a long line of research and nomenclature controversies the International Commission on Zoological Nomenclature officially renamed Plasmodium falciparum in 1954[23]). 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.[24]

However, Laveran's announcement was received with skepticism mainly because by that time leading physicians such as Theodor Albrecht Edwin Klebs and Corrado Tommasi-Crudeli claimed that they had discovered a bacterium (which they called Bacillus malariae) as the pathogen of malaria. Laveran's discovery was widely accepted only after five years when Camillo Golgi confirmed the parasite using better microscope and staining technique.[8]

Laveran was a supporter of the mosquito-malaria theory[4] developed by British physician Patrick Manson in 1894, and experimentally proved by Ronald Ross in 1898.[8] Based on this medical development, he reported malaria condition of Corsica in 1901 urging the need for eradication and control of mosquitos. The French Academy of Medicine established Ligue corse contre le Paludisme (The League of Corsica to Combat Malaria) with Laveran as its honorary president in 1902.[25]

Laveran came across another protozoan disease, cutaneous leishmaniasis, caused by different species of Leishmania, at Biskra, where it was known as clou de Briska (Biskra button) because of the obvious button-like skin sores in infected individuals.[26] Although he failed to make valuable observations, he was the first to identify the causative protozoan of a similar disease, now called visceral leishmaniasis. In 1903, while at the Pasteur Institute, he received the specimens from a British medical officer Charles Donovan from Madras, India, and with the help of his colleague Félix Mesnil, he named it Piroplasma donovanii.[27][28] However, the scientific name was corrected to Leishmania donovani the same year.[29][30] In 1904, he and M. Cathoire reported the first case of infantile leishmaniasis from Tunisia.[31] He published a treatise on leishmaniasis in 1917.[6]

Laveran later worked on the trypanosomes and showed once again that the protozoans were responsible for the disease such as sleeping sickness and animal trypanosomiasis.[32] He described Trypanosoma theileri from cattle in 1902;[33] Trypanosoma nanum in 1905 and Trypanosoma Montgomeryi in 1909, which were later corrected as Trypanosoma congolense, a parasite of nagana in cattle and horses.[34] With Mesnil, he identified Trypanosoma granulosum from European eels in 1902;[35] Trypanoplasma borelli[36] and Trypanosoma raiae from fish in 1902; Trypanosoma danilewskyi from fish in 1904;[36] and published a monograph Trypanosomes and Trypanosomiases (Trypanosomes et Trypanosomiases) in 1904[37] by which more than thirty new species were described.[4]