Another ally of the Trypanosomidæ, Trypanophis, lives in the cœlenteric cavity of Siphonophores. It has also an extra terminal flagellum (Poche, Keysselitz). [Trypanoplasma and Trypanophis belong to the Bodonidæ, see p. 63].
Finally it was shown that Trypanosomes occurred in human beings. Although Nepveu’s early report of trypanosomes in the blood of malarial patients may be doubtful, subsequent researches by Forde and Dutton demonstrated trypanosomes (fig. 28) in the blood of a European, apparently suffering from malaria, living in the Gambia. Dutton (1902) called the human trypanosome, T. gambiense. The expedition despatched by the Liverpool School of Tropical Medicine (1902) to Senegambia found trypanosome infections in six cases among a thousand inhabitants examined.
About the same time attention was devoted to the disease of West African negroes known for a century as “sleeping sickness.” Castellani (1903) was the first to succeed in demonstrating the presence of trypanosomes (at first called T. ugandense) in centrifugalized cerebro-spinal fluid obtained by puncture from cases of sleeping sickness in Uganda. Similar discoveries were made by Bruce, who also found trypanosomes in the blood of those attacked with sleeping sickness. Sambon regarded a species of Glossina as the transmitter. From consideration of the geographical distribution of the disease Christy regarded Glossina palpalis as the transmitter. Brumpt first thought it was G. morsitans, but, later, supported the view of G. palpalis. Bruce, Nabarro and Greig also named the same insect as the transmitter, not only for geographical reasons but also because healthy apes became infected by the bite of certain G. palpalis. The inoculation of cerebro-spinal fluid from subjects of sleeping sickness into the spinal canal of apes (Macacus) had the same result.
Just as the discovery of the malarial parasites called forth a whole flood of research memoirs which were followed by a second series on the relation of the mosquitoes to malaria, so a similar outpouring occurred after the discovery of the pathogenic trypanosomes of mammals and men. In both cases the inquiry was not limited to the stages in man and other vertebrate hosts, but the fate of the parasites in the intermediate (invertebrate) hosts was investigated, and allied species were obtained from many different hosts.
Novy and MacNeal (1903) were the first to cultivate trypanosomes in artificial media (blood-agar).
In 1910 Stephens and Fantham recorded the presence of another human trypanosome, T. rhodesiense, from a case of sleeping sickness in Rhodesia, where G. palpalis was absent. Kinghorn has since demonstrated that T. rhodesiense is transmitted by G. morsitans. Kinghorn and Yorke believe that big game (e.g., antelope) is the reservoir of T. rhodesiense.
The output of literature on trypanosomiasis in men and animals is enormous. To cope with it the Sleeping Sickness Bureau Bulletin was founded in 1908, and it is now (since November 1912) continued as a section of the Tropical Diseases Bulletin, wherein current literature is reviewed.
General.
Trypanosomes occur in the blood of representatives of all the vertebrate classes. Often the trypanosomes occur so scantily in the blood that they are overlooked on examination. A useful aid in detecting the flagellates in such cases consists in the use of cultures of the blood of the host on artificial media. Stimulated by the medium multiplication occurs, and hence the parasites are more easily detected. [For the composition of such culture media see Appendix.]
There is a periodicity in the appearance of the trypanosomes in the peripheral blood of the host, due to alternating phases of multiplication and of rest on the part of the parasites. Such periodicity has been established both by biological and enumerative methods. Again, a seasonal variation has been observed in the occurrence of certain trypanosomes in the peripheral circulation of the hosts; for example, some trypanosomes (e.g., T. noctuæ in birds) are found only in the summer in the blood, while in the winter they occur in the internal organs.
Recent cultural researches have established that trypanosomes, e.g., T. americanum, may be present in very small numbers in hosts, such as cattle, which are quite unharmed by them, and in which the presence of these flagellates formerly was never suspected (“cryptic trypanosomiasis.”) However, the majority of the trypanosomes occurring in domestic animals are usually deleterious or even lethal to their hosts. Many wild animals, such as various species of antelope, harbour trypanosomes without being injured thereby. In such cases it is probable that the vertebrate hosts have been so long parasitized in the past, that they have become tolerant and immune to the effects of the flagellates. Should such trypanosomes of wild animals be transmitted to domesticated stock or man, they may re-acquire their initial virulence and become pathogenic to the new host. As a general statement, the newer a parasite is to its host the greater is its virulence. For example, T. gambiense, T. rhodesiense and T. brucei are innocuous to big game in Africa, but are pathogenic to man and domestic animals respectively. Pathogenic trypanosomes appear to have a wider range of hosts, that is, to be less limited to one specific host than non-pathogenic forms. Thus, T. rhodesiense is pathogenic to man and all laboratory animals, while it is non-pathogenic to antelopes and their kind.
Morphology.
The general structure of the various trypanosomes shows much uniformity, though variations in size and shape occur. Typically the body is elongate and sinuous. The flagellar end tapers gradually to a point, the aflagellar extremity usually being rounded or more blunt. In some trypanosomes there is much diversity in size, the organisms varying from long, slender forms to short, stumpy ones; in other species relative constancy of size is maintained. The former are known as polymorphic trypanosomes, the latter as monomorphic forms.
Fig. 26.—Trypanosoma brucei in division. n, nucleus; bl, blepharoplast; fl, flagellum. × 2,000. (After Laveran and Mesnil.)
Two nuclei are present. The main or principal nucleus, sometimes termed the trophic nucleus, is often situated towards the centre of the body; it is frequently of the vesicular type, containing a karyosome. The blepharoplast or kinetic nucleus is posterior to the nucleus, and usually is rod-like. The flagellum arises close to the blepharoplast, and forms an edge to the undulating membrane. It may or may not extend beyond the limits of the undulating membrane. If it does so, the unattached part is known as the free flagellum. Sometimes a small granule is found at the origin of the flagellum. This is the basal granule, and is considered by some to function as the centriole of the kinetic nucleus.
The undulating membrane is a lateral extension of the ectoplasm or periplast, and is the main agent in locomotion. It is edged by the flagellum, which forms a deeply stainable border to it. Within the membrane substance, often arranged parallel with its edge, are a number of fine contractile elements, the myonemes. These contractile elements may also occur on the body of the trypanosome. They are easily seen in some large trypanosomes, but are difficult of demonstration in others, owing to their great fineness.
Fig. 27.—Trypanosoma lewisi. Multiplication rosettes. × 1,000. (After Laveran and Mesnil.)
Multiplication of trypanosomes in the blood is brought about by binary longitudinal fission (fig. 26). Division is initiated by that of the blepharoplast and nucleus. The division may be equal or subequal, whereby differences in size of individuals partly arise. Multiple division by repeated binary fission, without complete separation of the daughter forms, is