Spirochætes occur in the crystalline style and digestive tract of many bivalve molluscs. The first molluscan spirochæte to be studied was that of the oyster, named by Certes (1882) “Trypanosoma” balbianii (fig. 53). Similar spirochætes, probably belonging to the same species, occur in various species of Tapes and in Pecten (the scallop). S. balbianii has rounded ends (fig. 53). Other spirochætes occur in freshwater mussels (Anodonta spp). S. anodontæ, studied by Keysselitz (1906) and by Fantham (1907), has pointed ends. Gross (1911) suggested the generic name Cristispira for molluscan spirochætes, because they possess a well-marked membrane or “crista,” which appears to be absent from S. plicatilis, according to Zuelzer’s researches.
Schaudinn in 1905 founded the genus Treponema for the parasite of syphilis (T. pallidum), discovered by him and by Hoffmann. According to Schaudinn the Treponemata have no membrane or crista. The pathogenic agent of yaws or frambœsia, discovered by Castellani, is also placed in the genus Treponema, as T. pertenue.
There remain the blood spirochætes. It is somewhat disputed as to whether these organisms possess a membrane. The present writer considers that they have a slight membrane or crista. The name of the genus in which to place the blood-inhabiting forms is somewhat uncertain and disputed. Various generic names given to them are Spirochæta, Treponema, Spiroschaudinnia (Sambon) and Borrelia (Swellengrebel). Included in this division are the causal agents of relapsing or recurrent fever. These Protists will be named, for description, Spirochætes without prejudice as to the ultimate correct generic name.
It is sometimes made a matter of argument as to whether the spirochætes are Protozoa or Bacteria. Such arguments are somewhat unprofitable. Morphologically the spirochætes are like the Bacteria in possessing a diffuse nucleus. They differ from Spirillum, an undoubted bacterial genus, in being flexible and not possessing flagella. Molluscan spirochætes, however, may appear to have flagella if their membrane becomes frayed or ruptured, when the myonemes therein (fig. 53), becoming separated, form apparent threads or flagella (Fantham, 1907–08).142
Again, the mode of division of spirochætes has been used as a criterion of their bacterial or protozoal affinity. They have been stated to divide transversely, longitudinally, and by “incurvation,” or bending on themselves in the form of a U, “a form of transverse fission.” The present writer believes that they divide both transversely and longitudinally, and that there is a periodicity in their mode of division at first longitudinal (when there are few spirochætes in, say, the blood) and then transversely (when spirochætes are numerous in the blood).143 Some authors consider that longitudinal division is explained by “incurvation.”
The spirochætes of relapsing fever show a remarkable periodic increase and decrease in numbers in the blood. They are transmitted by ticks or by lice. They react to drugs (e.g., salvarsan or “606”) rather like trypanosomes, and—like Protozoa, but unlike Bacteria—they are cultivated with difficulty. These and other criteria have been used to endeavour to determine whether they are Protozoa or Bacteria. The present writer believes that they are intermediate in character, showing morphological affinities with the Bacteria and physiological and therapeutical affinities with the Protozoa. The group Spirochætacea, as an appendix to the Protozoa, has been created for them by the present writer (Jan., 1908). Others have placed them in the Spirochætoidea of the Bacteria or with the Spirillacea. Doflein (1909) called them Proflagellata. Further discussion is unnecessary, as they are undoubtedly Protista (see p. 29).
There is no true conjugation, sex or encystment in spirochætes, but morphological variation may occur.144 They may agglomerate.
The Spirochætes form an interesting chapter in the evolution of parasites. There are free living forms, parasitic forms in the guts of both vertebrates and invertebrates, and blood-inhabiting forms. These probably represent the order of evolution of parasitism. The blood-inhabiting forms are pathogenic to warm-blooded hosts.
We must now consider the blood Spirochætes and the Treponemata (organisms of syphilis and of yaws).
THE SPIROCHÆTES OF THE BLOOD.
There are at least two important human parasites included hereunder:—
(a) Spirochæta recurrentis (=S. obermeieri), (b) Spirochæta duttoni.
More is known of the life-cycle of Spirochæta duttoni, and it will be convenient to consider that first.
Spirochæta duttoni, Novy and Knapp, 1906.
The specific name duttoni was also given, independently, to this parasite in 1906 by Breinl and Kinghorn.
S. duttoni is the pathogenic agent of African tick fever in man, prevalent in the Congo State and other parts of Africa. The full-grown organism is about 16 µ to 24 µ long, and has pointed ends. It is 0·25 µ to 0·5 µ broad. P. H. Ross and Nabarro were among the earliest to see a spirochæte in the blood of patients in Uganda. It is transmitted by the tick, Ornithodorus moubata.
In the blood of the patient some of the spirochætes may show, after staining, lighter and darker portions (chromatin dots) and evidence of the possession of a very narrow membrane (fig. 54). The mode of division has already been discussed. Periodicity in the direction of division was first described by Fantham and Porter,145 (1909). Just before the crisis in African tick fever, Breinl has stated that S. duttoni becomes thinner in the spleen and bone-marrow and rolls up into skein-like forms, which are surrounded by a thin “cyst” wall (probably the periplast). Such occur in apyrexial periods. Inside the cyst the spirochæte breaks up into granules. Balfour and Sambon have described somewhat similar rolled up forms, breaking into granules, inside the red blood cells of Sudanese fowls in the case of S. granulosa (possibly only a variety of S. gallinarum). The intracorpuscular stage is not definitely established.
Fig. 54.—Spirochæta duttoni. a, blood form showing slight membrane; b, granules or coccoid bodies clearly formed within the organism; c, beginning of extrusion of coccoid bodies in the tick. (After Fantham.)
The granule phase, however, is an essential one in the invertebrate transmitter (fig. 54c). In 1905,146 Dutton and Todd proved experimentally that O. moubata transmitted S. duttoni. They fed ticks, obtained from Congo native huts in which infected persons lived, on monkeys and the latter became infected. Dutton and Todd also found the offspring of infected ticks to be capable of transmitting the infection to experimental animals. They concluded that O. moubata was a true intermediate host.
A little later in 1905, Koch stated that spirochætes from the gut of the tick penetrated the gut wall and tissues and found their way into the eggs in the ovary. Koch figured tangled masses of spirochætes as occurring in the tick eggs. He found ticks infective to the third generation. He thought that the infection was spread by the salivary fluid of the tick, in the act of biting. (This is now known to be incorrect.) Markham Carter (1907) corroborated Koch’s work on the spirochætes in the tick eggs, and they have been seen since by Kleine and Eckard (1913).
Sir William Leishman,147 in 1909–10, found that at ordinary temperatures the salivary glands of infected ticks (O. moubata) were not themselves infective, and that the infection occurred by way of the ticks’ excretion. The spirochætes (contained in the ticks’ excrement) found their way into the vertebrate host through the wound made by biting. While feeding, ticks pass large quantities of clear fluid from the coxal glands; in this fluid an anticoagulin occurs. Some of the ticks also pass thick, white Malpighian secretion, that is, excrement, towards the end of the feed. Leishman, using experimental