Page:Tropical Diseases.djvu/186



Definition.—— Morbid conditions produced by parasites belonging to the genus Trypanosoma, including irregular chronic fever, skin eruptions, local œdema, adenitis, physical and mental lethargy, and, in a large proportion of cases, death. History.—— Although its true etiology was not apprehended until quite recently, sleeping sickness, the terminal phase of African trypanosomiasis, has been known for over a century.

The occurrence of trypanosomes in animals has been recognized for at least sixty years, first in cold-blooded vertebrates, later in mammals. The best-known and first-described mammalian species is that of the rat (Trypanosoma lewisi). It was discovered by Lewis, in 1879, in Calcutta. In the following year Evans described a similar parasite (T.evansi) in the blood of horses in India; he found that it also infests camels, elephants, buffaloes, and dogs, and that it is the cause of the disease called " surra," which, from time immemorial, the natives of India have ascribed to the bite of certain blood-sucking flies. Fifteen years later Bruce showed that nagana, the " fly disease " of horses, bovines, and other species of domestic mammals in Africa, is due to the same kind of organism (T. brucei). Since these discoveries were made trypanosomes have been found in many species of mammals, as well as in numerous birds, fishes, and reptiles. Though differing in degree of virulence, they all, at least in mammals, give rise to a more or less similar type of disease.†