Human Trypanosomiasis in Rhodesia

Abstract

(1) Human trypanosomiasis (T. rhodesiense) has been known to occur in Rhodesia since 1911. Despite the fact that this disease spread in an epidemic form northwards in Africa about this time, no epidemic occurrence has been reported south of the Zambezi river, although the scattered and sparse population of human beings living in small villages in close association with tsetse fly and game animals seemed to provide conditions suitable for epidemic spread. (2) The cases reported in anyone year or period of years of indigenous origin have 'been small in number and at anyone period have been traceable to infection contracted at an endemic focus of limited size; even a single village, in one instance, constituted the focus. Four such endemic foci have been in operation--one after the other, over nearly 60 years. (3) The endemic foci have all been located on the Zambezi river side of the central watershed. No cases of human trypanosomiasis have ever been reported in Rhodesia in the Sabi-Lundi tsetse fly area. (4) It has been found that each endemic focus appears to be based on one or more ""healthy"" carrier cases of the disease, persons with a trypanosome infection of their blood stream who are not ill and continue in their normal pursuits and provide a ready source of infection for local tsetse fly. (5) Visits to an endemic focus by persons who live in fly-free areas, whether they be Africans or Europeans, result in a number of cases of acute trypanosomiasis, and it is the occurrence of a series of such cases that generally draws attention to the existence of such a focus. It appears that the indigenous African population living in the focus do not succumb to the infection readily, and even when they do contract the disease it seems to run a more chronic course. (6) The problems of the identity or otherwise of T. brucei and T. rhodesiense are discussed. If T. rhodesiense is merely T. brucei inoculated into a human being, one would expect cases to occur widely in tsetse fly areas where T. bruce; abounds. This is not so. (7) If T. rhodesiense is a human parasite able to maintain itself over the years by passage through game animals, the surprising localisation of cases is difficult to explain. It may, however, be a very rare parasite even in the Zambezi basin, where it is considered to have had its origin. If, however, it is inoculated into a person who, although developing a heavy blood infection does not develop cerebral symptoms and a progressive deterioration of health, a ""healthy"" carrier is created and may be the source of the build-up of a more frequent T. rhodesiense infection of the tsetse fly in a particular locality. (8) It is difficult to explain the tolerance of the ""healthy"" carrier to his infection and the general resistance of the indigenous inhabitants of an endemic focus to infection. It may be that the constant assault by tsetse fly infected with T. vivax and T. congolense may create some degree of non�specific resistance to infection with T. rhodesiense when this infection is introduced by a tsetse fly. It is also possible that when an individual not previously exposed to tsetse fly, enters a focus in which cattle and human strains exist, the great chances are that he will be inoculated with one of the non-human trypanosomes. These trypanosomes do not survive in him, but induce a temporary acquired immunity which depends on repeated inoculation of non-human trypanosomes. Should such a person then be inoculated with the much rarer human strain, he will not develop trypanosomiasis unless his state of immunity is not fully protective, in which event he will contract a mild form of the disease or become a ""healthy"" carrier. (9) In investigating an endemic focus it is important to examine all the people in the area, including those temporarily absent. Blood films must be taken from all the inhabitants and not only those who are ill, have temperatures or have enlarged cervical glands. If a ""healthy"" carrier is present he will be active and well and strenuously deny that he is in any way ill.