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Abstract

The trypanosomes of mammals. A zoological monograph.

Abstract

Until this book appeared, no monograph on the trypanosomes had been written since 1912, when LAVERAN and MESNIL [see this Bulletin, 1913, v. 1, 522] issued the second edition of their famous treatise on trypanosomes and trypanosomiasis. In the meantime, the number of species of mammalian trypanosomes has nearly quadrupled and the medical and veterinary importance of these organisms has been discussed in many general textbooks of protozoology, parasitology and related subjects, culminating in the most recent work "The African trypanosomiases ", edited by MULLIGAN [ibid., 1971, v. 68, abstr. 1893]. The nearest approach to a definitive account of the trypanosomes was contained in Volume 1 of WENYON'S " Protozoology. A manual for medical men and veterinarians" [ibid., 1926, v. 23, 854], but the latter was written about 50 years ago and the need for a modern description has been increasingly felt. Hoare's book exactly meets this need. His book is subtitled " A zoological monograph ", but the environment in which the author has lived and worked for more than 50 years (in the Wellcome Laboratories of Tropical Medicine) has ensured that Wenyon's viewpoint is shared by his most famous pupil, and a practical rather than a strictly academic treatment of controversial matters is applied throughout the monograph. Thus, more than half of the systematic part is devoted to the trypanosomes of man and his domestic animals. Nevertheless, the book is written by a zoologist for zoologists; it is a treatise on the trypanosomes rather than on trypanosomiasis. The biochemistry and physiology of the organisms are only briefly considered, and when these aspects have a direct bearing on structure in different stages of the life history (e.g. mitochondrial respiration). However, the book will be essential for biochemists and physiologists, working with trypanosomes, as constituting the fundamental basis for their studies. Similarly, it will be required by all people who work on trypanosomiasis as a disease, and excellent sections are devoted to pathogenesis, host-parasite relationships and epidemiology.
Part 1 consists of 7 chapters dealing with general features, of which the most important are " Classification ", " Evolution " and " Host-parasite Relationship ". The author has played a large part in establishing a logical classification for mammalian trypanosomes from the Family level to the " demes ". Hoare realizes that at present the concept of demes or microevolutionary variants can have no taxonomic value. The terminology for stages in the life cycle which he and WALLACE introduced in 1966 [ibid., 1967, v. 64, 599] has been widely adopted. Possibly the chapter on evolution is the most interesting in the whole book; it embodies many of the author's own ideas on this largely hypothetical subject. Among host-parasite relationships are considered the Nicollean concepts of infection and resistance, as well as the relevance of animal reservoirs in medical and veterinary zoonoses. These subjects are considered in much greater detail in particular examples in the systematic part of the book.
Part 2 consists of a complete description of the species (and lower categories) of the mammalian trypanosomes, and is divided into two sections-the Stercoraria (with 3 subgenera, Megatrypanum, Herpetosoma and Schizotrypanum) and the Salivaría (with 4 subgenera, Dutionella, Nannomonas, Trypanozoon and Pycnomonas).
Data on some Stercorarian parasites may be scanty or imprecise and it has often been necessary to give a collective account of a group, e.g. " cruzi-like trypanosomes of bats ", and to summarize the conclusions in shorter sections. On the contrary, much more information is available about the Salivarían trypanosomes, and each species is considered separately. The general plan, however, is similar throughout the systematic part and consists of the following points: -
Synonymy, history (in great detail and invaluable for reference purposes), distribution and natural (vertebrate) hosts, life cycle and morphology (including culture and methods of transmission), host-parasite relations (including the course of infections in the vertebrate, the clinical manifestations of disease and pathology, behaviour in experimental animals and immunity), and epidemiology (or epizootiology). In some of the lesser known species, certain of these aspects may be omitted; in the better known species, others may be added, e.g. phylogenetic relations, diagnosis (though technical 'details are beyond the scope of the monograph).
Workers in Africa will be glad to haye an authoritative statement on the Trypanosoma brucei complex, which is here considered to comprise two subspecies: T. b. brucei and T. b. gambiense. T. rhodesiense is regarded as the rhodesiense variant or nosodeme of T. b. gambiense and thus loses its taxonomic identity. The epidemiology of these trypanosomes is discussed from several angles which give interesting perspectives: historical, geographical, ecological, entomological, zoonotic pattern, carrier state, etc. Equally fascinating are the author's theories on the development and spread of the T. evansi complex, which are of profound significance, as permanent changes in methods of transmission, zoogeography and even morphology have taken place. The veterinarian will find useful the chapter on the subgenus Nannomonas, and the validity of its various species. The pathogenesis of T. theileri is an interesting subject as it concerns the probably synergistic effect of other protozoans or viruses on the trypanosome infection, but the final story has yet to be told. The occurrence of closely related, if not identical, trypanosomes in certain groups of animals presents much 'difficulty in classification, particularly the crwzMike trypanosomes in various mammals (and their relation to T cruzi itself); in the organisms found in, monkeys (including the controversial species found in Asian macaques [ibid., 1970, v. 67, abstr. 2108]) and the lewisi-like, trypanosomes in rodent and other small mammals. The mechanism of immunity in T. lewisi infections is still not completely settled, but the theories are briefly discussed in an introductory chapter (VII). The author makes it abundantly clear that much basic information is still lacking in our knowledge of the trypanosomes in general, and even the life cycles of many species remain undiscovered.
The illustrations are of the greatest value and consist of 108 figures, chiefly of line drawings, made by the author from his own preparations, or redrawn from originals at a standard magnification of X1600, and also of lucid diagrams of life cycles and of a few hosts. In addition there are 3 superb coloured plates of blood forms of trypanosomes from paintings by B. JOBLING at a magnification of XI800.
The monograph contains a useful check list of mammalian hosts of trypanosomes in the following orders: -
MONOTREMATA, MARSUPIALIA, EDENTATA, LAGOMORPHA, RODENTIA (in the greatest number), INSECTÍVORA, CHIROPTERA (second most numerous), PRO-BOSCIDEA, PERISSODACTYLA, ARTIODACTYLA (third most numerous), CARNÍVORA and PRIMATES. The list of the hosts contains the latest names and includes indications of locality and selected recorders. The very extensive bibliography (over 1600 references) concentrates on the most recent publications and comprises references from the widest range of journals.
This monograph, written in the clearest English and beautifully produced, will remain the standard work on the subject for many years and will occupy a high rank in the classics of protozoology. P. C. C. Garnham.