Informed speculation on the cause of sleeping sickness 1898-1903.

THE incrimination of the trypanosome as the cause of sleeping sickness and the discovery of the transmission of the parasite by the tsetse fly was the result of studies carried out in Uganda by Castellani, Bruce, Nabarro and others.' While there is no question of the importance of their elucidation of the relation between the disease, the parasite and the vector, by clinical, laboratory, and field work, the long controversy over the attribution of credit between these workers that continued for so many years' has tended to obscure the interesting fact that informed speculation by others, with very varying experiences of the disease, had pointed to all the aspects of the situation which were later shown to be important, the parasite, the vector and aspects of the ecologic situation. The early history of sleeping sickness has often been recorded and Hirsch2 summarized existing knowledge and theories of the 1880s and this was brought up to date in a clinical lecture delivered by Patrick Manson at Charing Cross Hospital in 1898.3 He had seen in consultation the two patients of Stephen Mackenzie's some years previously and it was in the blood of these that the filaria, Dipetalonema perstans, was first identified. Manson had two patients of his own to dilate on in the clinical lecture and was much influenced by the little African boy who had been sent from the Congo to a school in Wales where after a long interval he had developed sleeping sickness. The boy had not been unhappy in this Welsh school, no other children had been affected, the boy had not been consuming manioc, or raw fish, or palm wine and certainly had not been indulging in excessive venery. The Welsh sun was hardly strong enough to penetrate the negro cranium and injure the brain. While existing evidence in Africa pointed strongly to sleeping sickness being an infective disease no cases had developed in the West Indies from contact with imported slaves who had developed the disease. The most careful bacteriological studies of blood and of the enlarged lymph glands in the patients seen in England had been entirely negative but in the blood of all cases Dipetalonema perstans had been found. The cause of the disease in the boy seemed to be some infectious agent only contracted in his Congo homeland which, after a long incubation period, caused the disease. Manson thus indicated the conditions that any aetiologic suggestions must explain. These were: causation by a living agent, one capable of remaining latent in the body for long periods, only acquired in certain localities, not capable of being introduced into some virgin areas, one not spreading directly from person to person but dependent, directly or indirectly on the flora or fauna in certain localities. Everything in the epidemiology of sleeping sickness pointed, in Manson's view, to its being due to some living agent that had, at some stage or other in its existence, to pass through the body of a lower animal, or possibly a plant found only in certain equatorial areas of Africa. Of the possible candidates for the dubious honour Manson considered that a case could be made for Dipetalonema perstans though he recognized some difficulties. Firstly it has been found in Guyana whence sleeping sickness had never been recorded and this would be a fatal objection were it not that Dr. Ozzard4 considered that such