Page:Tropical Diseases.djvu/230

196 was discovered by Bruce in 1895 in the blood of horses suffering from nagana, the fly disease of Africa. The normal intermediary hosts of T. brucei are probably some of the African Antelopidae, such as the wildebeest (Catoblepas gnu), the koodoo (Strepsiceros capensis), and the bushbuck (Tragelaphus scriptus sylvaticus), perhaps also buffaloes. Bruce's researches and experiments led to the belief that the disease was transmitted in a mechanical way by Glossina morsitans. Mr. Austen has shown that the tse-tse -flies with which Bruce made his experiments belonged chiefly, if not entirely, to the species G. pallidipes, and now we know that other glossinae, such as G. fusca, may also convey the disease, and that the role played by these flies is probably that of true alternative host. The development in the fly is identical with that described for gambiense. The fly does not become infective till the eighteenth, and remains so till the sixty-sixth day, or probably longer.

With the exception of certain strains of donkey and goat, all domesticated mammals hitherto experimented with, on inoculation with blood containing the parasite, acquire nagana.

After inoculation of an animal with nagana blood, in from one to two days trypanosomes begin to appear in the blood, and persist therein till death, which, in the vast majority of species, is inevitable. In some species (rats, mice) the trypanosomes become very numerous; in others (the rabbit, guineapig) they are scanty and may be hard to find with the microscope, although their presence may readily be proved by the symptoms and by injection of the suspected blood into the rat. After inoculation death occurs in rats and mice in from two to three days, in rabbits in from five to twelve days, in guineapigs in about fifty days (extremes twenty to 183 days), in dogs in from twenty-two to twenty-six days, in monkeys in fifteen days, in horses and donkeys in from one week to three months, in goats and sheep in several months, and in cattle in from one week to six months, a proportion recovering. Thus resistance varies within wide limits.

In those animals in which death occurs within a few days of infection the parasites become very numerous, and, after one or two oscillations of temperature, death occurs suddenly. In those animals in which death is delayed a very striking cachexia is established. There is a chronic recurring fever, the numbers of parasites visible in the blood being greatest during the febrile accessions; there is also a peculiar firm oedema from infiltration of coagulable lymph into the connective tissue of the neck, abdomen, sheath of penis, genitals, and limbs; with intense anaemia, wasting, skin eruptions, and, often, blindness. On post-mortem examination the spleen is in most instances found to be enlarged, ecchymoses may be present in various viscera, and the lymphatic glands corresponding to the point of inoculation are swollen.

T. brucei is considered by Bruce and several other observers to be the cause of Rhodesian sleeping sickness, and therefore identical with T. rltodesiense.