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The Subspecific Taxonomy of Trypanosoma Brucei

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The Subspecific Taxonomy of Trypanosoma Brucei Article available at http://www.parasite-journal.org or http://dx.doi.org/10.1051/parasite/1995021003 T he subspecific t a x o n o m y o f Tr y p a n o s o m a b r u c e i J. R. BAKER* S u m m a ry : Résumé : La t a x o n o m ie s o u s - sp é c if iq u e d e Trypa n o so m a br u c e i Trypanosoma brucei was first seen by David Bruce in 1894, in Trypanosoma brucei a été observé pour la première fois en 1894 the blood of a cow in South Africa, and named in his honour in par David Bruce, dans le sang d'une vache d'Afrique du Sud, et 1899. Trypanosomes seen in the blood of an Englishman in The ainsi nommé en son honneur en 1899. Gambia in 1901 were named T. gambiense in 1902. Finally, in Les trypanosomes observés dans le sang d'un anglais en Gambie 1909, trypanosomes from the blood of an Englishman in Zambia en 1901 furent appelés T. gambiense en 1902. Enfin, en 1909, ("Rhodesia") were named T. rhodesiense. Since then there has les trypanosomes provenant du sang d'un anglais en Zambie been continuous debate about the interrelationships of these three ("Rhodésie") furent appelés T. rhodesiense. Depuis, les interrelations "species". Studies of the molecular biology of these trypanosomes, entre ces trois "espèces" ont fait l'objet d'un débat continuel. L'étude mainly analyses of their isoenzymes and deoxyribonucleic acid, de la biologie moléculaire de ces trypanosomes, principalement now appear to have shown that T. "rhodesiense" cannot be distin­ l'analyse de leurs isoenzymes et acide désoxyribonucléique, sem­ guished from T. brucei brucei by any valid and consistent criterion, blent avoir montré que T. “rhodesiense" ne peut être différencié de T. while T. "gambiense" probably does constitute a valid subspecies brucei brucei par aucun critère valable et permanent, alors que T. of T. brucei. There is still doubt whether populations of T. brucei gambiense constitue vraisemblablement une sous-espèce de T. bru­ are predominantly clonal or sexual. W hile some form of genetic cei. Il persiste un doute quant au caractère principalement clonal ou exchange undoubtedly can occur in this species, its nature and fre­ sexuel des populations de T. brucei. Bien qu'une mutation génétique quency are unknown and there is evidence that the population puisse indubitablement survenir chez cette espèce, sa nature et sa structure of T. brucei is essentially clonal. fréquence sont inconnues et il est démontré que la structure démo­ graphique de T. brucei est essentiellement clonale. KEY WORDS : Trypanosoma brucei. history, subspecific taxonomy, popula­ tion structure. MOTS CLÉS : Trypanosoma brucei. histoire, taxonomie sous-spécifique, structure démographique. BACKGROUND foundation of stones (Joubert et a l., 1993; Cook, 1994). Bruce started his investigation by examining daily the n November 1894, just over 100 years ago, David blood of a ‘brown cow’ suffering from n ag an a. He Bruce (Fig. 1) (then a captain in the British army observed bacteria, which he at first thought were pro­ and subsequently knighted as Sir David) and his bably the cause of the disease, but on the sixth day Iwife Mary arrived in a small village (‘a magistrate’s he recorded in his notes the presence of office and a few mud huts’ : Joubert et al., 1993) cal­ ‘Haematozoa’ (MacArthur, 1955). He subsequently led Ubombo ( O bon jen i in the local language, accor­ admitted (Bruce, 1915) that he originally thought ding to Joubert et a l., 1993) in KwaZulu, Natal these ‘Haematozoa’ were small filariae, but within a Province, South Africa. They had been sent there by short time (probably before the end of 1894) Bruce the military authorities to try to discover the cause of had concluded that the haematozoa (Fig. 3) were the a disease known as n a g a n a which was devastating cause of n a g a n a and also of ‘tsetse fly disease’ of the cattle of the inhabitants of the region and the humans, which until then had been thought to be a horses used by the administrators of what was then a separate entity (Bruce, 1895, 1896). A few years later British colony. the ‘Haematozoon’ was named by Plimmer and Bruce and his wife established their home (and labo­ Bradford (1899) as Trypanosoma brucii [sic], Bruce ratory) in a rectangular building (Fig. 2), built mainly having sent an infected dog to England. The specific of mud on a framework of wattle (interlaced name, whether printed thus due to a typesetter’s error branches of small trees and shrubs) apparently with a or a lapse on the part of the authors, was soon cor­ rected to T. bru cei (Nabarro, 1907, p. 112 footnote 1, stated that the change was made by Laveran and * Royal Society of Tropical Medicine and Hygiene, Manson House, Mesnil, but cited no reference). 26, Portland Place, London, W 1N 4EY, England. Parasite, 1995, 2, 3-12 Mise au point 3 J. R. BAKER Fig. 2. - David Bruce’s hut in Ubombo, 1894-1895 (from Bruce, 1915 : Lancet, ii, 1-6; photograph kindly supplied by Dr G.C. Cook [see Cook, 19941). Fig. 1. - David Bruce (photograph taken probably in 1917, and kindly supplied by courtesy of the Administrator, Royal Society of Tropical Medicine and Hygiene). Fig. 3. - Photograph of Dr J. E. Dutton (right) with, next to him, Mr H. Kelly, the first known case of human trypa­ nosomiasis (1901). One of the other tw o m en is Dr R. M. Forde; the iden­ tity of the second is not known. The original photograph is annotated in Dutton’s handwriting ‘The first case of trypanosomiasis’, with the names of Kelly and Dutton. Photograph kindly supplied by courtesy of Miss Patricia Miller, archivist, and the Photographic Department of the Liverpool School of Tropical Medicine. Parasite, 1995, 2, 3-12 4 Mise au point The subspecific taxonomy o f Tr y p a n o s o m a b r u c e i Fig. 4. - Sketches of ‘Haematozoa’ in the blood of a dog, from Plate V of Bruce (1895). Later, coloured drawings of trypanosomes in Bruce’s reports were made by Mrs (later Lady) Bruce; these sketches are cruder, and may have been drawn by Bruce him­ self (photograph kindly supplied by courtesy of Ms Mary Gibson, bibliographer, and the Visual Aids Department of the London School of Hygiene and Tropical Medicine). Only two years after the naming of T. brucei, in May Ronald Ross (who is now more famous for his colla­ 1901, a doctor in the British colonial service in The boration with Patrick Manson on the mosquito trans­ Gambia named R. M. Fordei saw, in the blood of a 42 mission of malaria). The case history of this patient years old Englishman (‘H. K.’), subsequently identified was reported by Ross and Thompson (1910, 1911); he from the archives of the Liverpool School of Tropical was subjected to a horrifying battery of attempted Medicine as H. Kelly; see fig. 4), who was master of a therapies for his condition, including atoxyl, quinine, government steam boat on the Gambia river, what he methylene blue, trypsin, amylopsin, succinamide of described as ‘small worm-like, extremely active mercury, ‘izal oil’ [presumably a commercial house­ bodies’ which he first thought were filariae. However, hold disinfectant of that name], trypan red, potassium later in 1901 J. E. Dutton, of the Liverpool School of iodide, ‘vaccines’ prepared from his own trypano­ Tropical Medicine, was visiting Bathurst in The somes grown in rats, and an extract of rat peritoneal Gambia. Forde showed his patient, and the ‘worms’ in leucocytes. On one occasion he was injected with 1 x his blood, to Dutton, who recognized them as trypa­ 109 ‘dead’ trypanosomes in rat’s blood; this, the doc­ nosomes (Forde, 1902). Dutton (1902) subsequently tors reported, ‘seemed to cause no harm’ (Ross and named the parasite T. gambiense. (Dutton actually Thompson, 1911). Perhaps not suprisingly, the unfor­ wrote ‘At present then it is impossible to decide defi­ tunate patient died on 29 June 1910. He was identi­ nitely as to the species, but if on further study it fied by Ross and Thompson (1910), and by Stephens should be found to differ from the other disease pro­ and Fantham (1910), only as ‘W. A.’, a native of ducing trypanosomes I would suggest that it be called Northumberland in the UK. Duggan (1970) named Trypanosoma gambiensé (p. 467); although this is a him as W. Armstrong, but gave the date of his infec­ ‘conditional proposal’ in the terms of the International tion as 1908; this seems to be a mistake. Code of Zoological Nomenclature (third edition, 1985, Before his death, trypanosomes were isolated from article 15), such proposals made before 1961 do not W. A.’s blood and studied (in rats) by Drs Stephen prevent availability of the name.) and Fantham at the Liverpool School of Tropical On 17 November 1909 trypanosomes were seen in Medicine. Stephens and Fantham (1910) noted the the blood of a 26 years old Englishman who had virulence of this strain, and reported the appearance been travelling along the valley of the Luangwa river of posteronuclear trypomastigotes in the rats’ blood in Zambia (then north-east Rhodesia); he was thought which (they thought) distinguished it from T. g a m ­ to have become infected there in September 1909. b ien se; they discussed the possibility that it was (i) a On 2 December he was admitted to the Royal ‘variety’ or ‘local race’ of T.
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