The Plague is an endemic disease in certain countries, particularly in India, from certain places of which it spreads and becomes universal. Some of the great scourges of history were caused by bubonic plague. Its chief features have been discussed under PLAGUE, and need not be repeated here.
Two comparatively new tropical diseases have, in recent years, been the subject of much careful investigation. These are trypanosomiasis, or the sleeping-sickness, and kala azar. Although both have been known from the clinical standpoint for many years, it has been only since 1900 that the determining causes have been discovered.
Sleeping-Sickness is an African disease of a very dramatic character : deadly and weird in its course, and made even more fascinating by the romantic literary handling that has been accorded it. It is very prevalent among the native races, and, in certain places, it is known to depopulate whole villages. It has been contracted by whites, in whom it runs a slightly different course. In the negro it starts with headache and a low fever. There is a very characteristic lassitude, the patient being tired and sleepy, and sitting about with a dejected, vacant countenance, with drooping of the lower lip. This persists for a month to six weeks, the lassitude deepening into a marked lethargy ; and in the second month the facial expression becomes even more listless, the upper eyelids droop, the face becomes puffy, and the patient seems half dead. At the end of three months the patient is in a much reduced condition, saliva drops from the lips, and there is a very evident dementia. The body becomes dirty, the arms are subject to a jerky tremor, there may be spasms in other muscles, and the patient becomes so stupid that he is unable to move about. During the fifth to sixth month he loses ground rapidly. Sores appear ; the lymphatic glands, particularly those of the cervical region, become swollen ; itching may be extreme ; con vulsions may occur ; the patient can no longer speak on account of paresis of the muscles and loss of intelligence ; and in from six to seven months death takes place by exhaustion, by epileptiform convulsions, or by some intercurrent affection (tuberculosis, pneumonia, etc.). The more rapidly
fatal cases terminate in death in three to four months ; other patients live two to three years and pass through a series of changes very highly suggestive of general paresis. See BRAIN, SOFTENING OF.
The changes in the brain are those of a diffuse meningo-encephalitis, with marked infiltration around the blood-vessels. The cause is a minute blood-parasite (Trypanosoma), which belongs to a group of well-known microscopic animal forms, the Protozoa. Since the opening up of Africa, the disease has spread from its original home in Western Africa from Sene gambia to Benguela, and has extended into the upper part of the Nile Valley ; and it threatens to become very widespread. As it has been a uniformly fatal disease, and its ravages have been very marked, killing 40,000 natives in Uganda alone in one year, its limitation is highly desirable. There is no recognised form of treatment, although Ehrlich has devised a trypan red which has some promise either in its original or modified forms. Related parasites are present in Texas cattle, causing the well-known Texas cattle fever, and thus it becomes of importance to bear in mind this parasite. Furthermore, the " surra " of the Philippines and the " mal de Caderas " of South America are both due to a trypanosome. As it is the case with Texas cattle-fever that a fly, the tsetse fly, is the agent of transmission, so it has been assumed that the Glossina palpalis, one of these flies, plays the same part for human trypanosomiasis. It is a very common fly of Africa, inhabiting the banks of lakes and streams, and is a fierce biter. Its habitat probably explains the observations of several travellers in Africa, that those whose occupations lead them to a life in the neighbourhood of streams (fishermen, boatmen, water-carriers, etc.) are much more liable to infection. Whole tribes who live on the borders of lakes have died of the disease, while agricultural communities inland have not suffered. A careful study of the wild tribes of South America may show somewhat similar conditions.