Fig. 67.—Life-cycle of Eimeria (Coccidium) schubergi, Schaud., from the intestine of Lithobius. (After Schaudinn.) The infection is caused by a cyst (XX), containing spores, which reaches the intestine of a Lithobius, where it discharges the sporozoites (I). II, A sporozoite invading an intestinal epithelial cell; III, intestinal epithelial cell with young trophozoite; IV, intestinal epithelial cell with a globular schizont; V, nuclear segmentation within the schizont; VI, the daughter nuclei arranging themselves superficially; VII, formation of the merozoites; VIII, merozoites that have become free, and which, penetrating into other epithelial cells of the same intestine, repeat the schizogony (II-VIII); IX and X, merozoites which, likewise invading the epithelial cells of the same intestine, become sexually differentiated; xia, young macrogametocyte; XIb, older macrogametocyte; XIc, mature macrogametocyte (discharging particles of chromatin); XIIa, young microgametocyte; XIIb, older microgametocyte; XIIc, increase of nuclei in the microgametocyte; XIId, the globular residual body around which numerous microgametes have formed; XIIe, an isolated microgamete; XIII, the mature macrogamete surrounded by numerous microgametes and forming a cone of reception or fertilization prominence; XIV, shows the nucleus of a microgamete that has penetrated and fused with the nucleus of the macrogamete (fertilization)—the latter forms a membrane and becomes an oöcyst; XV, XVI, XVII, nuclear segmentation in the oöcyst; XVIII, oöcyst with four sporoblasts; XIX, the sporoblasts transformed into spores, each containing two sporozoites; XX, the cyst introduced into the intestine and liberating the sporozoites by bursting.
The merozoites move in a manner similar to that of the sporozoites. The movements consist either of slow incurvations with subsequent straightenings, or annular contractions along the entire extent of the body. In addition, there are gliding movements similar to those of many gregarines, and brought about in a like manner by the secretion at the posterior extremity of a gelatinous substance that hardens rapidly.
The merozoites do not gain the open in the usual way, but are destined to infect still further the same host by actively penetrating into other epithelial cells of the affected organ. Here they continue their growth and may again and again undergo schizogony. In the Infusoria the repeated segmentations finally cease and are renewed only after a conjugation. This is likewise the case with the Coccidia, with the difference that in the latter the two conjugating individuals (gametes) are differently constituted one from the other, whereas in the Infusoria they are almost always similar.
When the schizogony ceases, the merozoites, that had penetrated the epithelial cells and become trophozoites there, consist of two kinds of differently constituted individuals. One kind possesses a clear cytoplasm (fig. 67, XII), the other an opaque, richly granular cytoplasm (fig. 67, XI), while both possess a vesicular nucleus with a karyosome. In order to continue their development, the more granular individuals must be fertilized, and are therefore termed either female gametes or, on account of their size, macrogametes. The male individuals (microgametes) necessary to conjugation, are formed in greater numbers from the less dense microgametocytes or male mother-cells (fig. 67, XIId). They are slender bodies consisting chiefly of nuclear substance, and in most species bear two flagella of unequal length directed backwards, the place of insertion of which varies according to the species (fig. 67, XIIe).
While the development of the microgametes is rapidly advancing a change occurs in the nucleus of the female parent forms or macrogametocytes. Parts of the karyosome are extruded (fig. 67, XIc), and the nucleus loses at the same time its vesicular form. One macrogamete results, after nuclear maturation, from one macrogametocyte. By this time the macrogametes are capable of conjugation, and the process takes place within the host, generally, however, outside the affected and degenerated host cells. The microgametes that have now become free from the very large residual body, crowd around the mature macrogametes, which often send out a small prominence (“cone of reception” or fertilization protuberance) for their reception (fig. 67, XIII). As soon as a microgamete comes in contact with this and penetrates into the cytoplasm of the macrogamete, the latter surrounds itself with a membrane which prevents the intrusion of other microgametes. The nucleus of the microgamete that has gained entry unites with the nucleus of the macrogamete, which latter is afterwards capable of forming the well-known spores. The parasite is now called an encysted zygote or oöcyst. The oöcysts of some other members of the Coccidiidea, e.g., Eimeria avium, can form their walls prior to fertilization. In such cases, a weak spot is left at one place in the cyst wall, forming a micropyle, that permits of the entry of the male, immediately after which the micropyle is closed.
The reduced nucleus of the macrogamete elongates on the entry of the microgamete, and becomes a fertilization spindle to which the male pronucleus (from the microgamete) becomes attached (fig. 67, XIV and XV). Thereupon the spindle divides into two daughter nuclei (fig. 67, XVI) which assume a round shape. The protoplasm at this stage may at once divide, or another segmentation of the daughter nuclei may first occur. In the former case the two halves divide again, so that finally four nucleated segments, the sporoblasts, are formed, whereas in the latter case the four sporoblasts appear simultaneously (fig. 67, XVII). In both cases a residual body of varying size is separated from the protoplasm of the oöcyst. As a rule the oöcysts have already been discharged from the body of the host, and in the manner described above, form the sporoblasts after a longer or shorter period of incubation.
The sporoblasts are originally naked, but each soon secretes a homogeneous membrane, the sporocyst, in which it becomes enveloped (fig. 67, XVIII). After the segmentation of the nucleus the contents divide into two sickle-shaped sporozoites, in addition to which there is generally also a residual body (fig. 67, XIX).
This terminates the development. The spores are intended for the infection of other hosts. If they reach the intestine of suitable hosts, either free or enclosed in the oöcyst wall, the action of the intestinal juices causes them to open and permits the escape of the sporozoites (fig. 67, XX). The latter move exactly like the merozoites and soon make their way into epithelial cells (fig. 67, I), where they become schizonts, and thus repeat the life cycle.
Although our knowledge of the development of the coccidia is but of recent date, yet it already extends to a large number of species, which exhibit various deviations from the cycle of development described above. For instance, in addition to differences in the gametocytes, the schizonts of Adelea and Cyclospora also show differentiation and give rise to macromerozoites and micromerozoites, whilst in Adelea and Klossia a precocious association of the gametocytes precedes the true copulation of the ripe gametes.
The classification of the Coccidiidea is based chiefly on the number of sporozoites found in each spore, and the number of sporocysts (spores) found in one oöcyst. Léger173 recognises two great legions, the Eimeridea and the Adeleidea, the former comprising the greater number of genera, including the genus of most economic importance, Eimeria. It must be noted that, though a member of this genus may be frequently referred to as Coccidium, strictly it should be termed Eimeria, that name having priority. The name of the disease resulting from the action of such parasites is, however, established and remains as coccidiosis.
Certain of the more important of the Coccidiidea may now be considered.
Genus. Eimeria, Aimé Schneider, 1875.
Syn.: Psorospermium, Rivolta, 1878; Cytospermium, Rivolta, 1878; Coccidium, R. Leuckart, 1879; Pfeifferia, Labbé, 1894; Pfeifferella, Labbé, 1899.
The Eimeria belong to Léger’s old family, the Tetrasporocystidæ, which comprises forms producing oöcysts with four sporocysts, each containing two sporozoites. The cysts are spherical or oval, as are also usually the schizonts. The members of the genus are confined chiefly to vertebrate hosts, the more important economically occurring in mammals and birds. From the mammalian hosts very rarely the parasites may reach man. Eimeria (Coccidium) avium of wild birds and poultry, and Eimeria stiedæ parasitic in rabbits, may be considered. There is a general similarity in their life-cycles and each is of great practical importance.
Eimeria avium, Silvestrini and Rivolta.
Eimeria avium is responsible for fatal epizoötics among game birds such as grouse, pheasants and partridges, and domestic poultry such as fowls, ducks, pigeons and turkeys, and can pass from any one of these hosts to any of the others with the same effect. The organism is parasitic in the alimentary tract of the host, affecting more especially the small intestine (duodenum) and the cæca, but in some cases penetrating to the liver and multiplying there (as in turkeys), producing necrotic cheesy patches, that ultimately become full of oöcysts. The gut is rendered very frail by the action of the parasites, its mucous membrane is greatly injured, and is often reduced to an almost structureless pulp, riddled with parasites (fig. 68). Infection is conveyed from host to host by the ingestion of food or drink contaminated with the oöcysts voided in the fæces of infected birds. Oval oöcysts from 24 µ to 35 µ long and from 14 µ to 20 µ broad are the means of infection. The oöcysts develop internally four sporocysts or spores, from each of which two sporozoites are produced. The life-history174 presents two phases: (1) The asexual multiplicative phase, schizogony, for the increase in numbers of the parasites within the same host; (2) the reproductive phase, following the formation of gametes (gametogony), leading to the production of resistant oöcysts, destined for the transference of the parasite to new hosts (sporogony).
The oöcysts usually reach the duodenum unharmed, with food or drink. Under the influence of the powerful digestive juices (especially the pancreatic) now encountered, the oöcysts soften, as do the sporocysts, and ultimately two sporozoites emerge from each sporocyst. The sporozoites are from 7 µ to 10 µ long, and each is vermicular with a uniform nucleus (fig. 69, A). After a short period of active movement in the gut, each sporozoite penetrates an epithelial cell (figs. 68 spz, 69, B), and once within, gradually becomes rounded (fig. 69, B, C). It grows rapidly, feeding on the contents of the host cell and living as a trophozoite (fig. 69, D). When the parasite is from 10 µ to 12 µ in diameter, usually multiplication by schizogony (fig. 69, E-H) begins. The nucleus of the parent cell, now called a schizont, divides into a number of portions that become arranged at the periphery (fig. 69, E). Cytoplasm collects around each nucleus (fig. 69, E, F) and gradually a group of daughter individuals (merozoites) is produced (fig. 69, G), the nucleus of each merozoite showing a karyosome.
Fig. 68.—Small piece of epithelial lining of gut of heavily infected Grouse chick, showing various stages in life history of the parasite Eimeria avium; par, parasite (trophozoite); mz, merozoite; sch, schizont; spz, sporozoite; ooc, oöcyst; ♂, male gametocyte; ♀, female gametocyte. × 750. (After Fantham.)
The merozoites of Eimeria avium are arranged “en barillet,” like the segments of an orange (figs. 68 mz, 69, G), therein differing from those of E. schubergi, which are arranged “en rosace.” They separate from one another (fig. 69, H), penetrate other epithelial cells, where they may, in turn, become schizonts. Eight to fourteen merozoites are usually formed by each schizont, twenty have been found, while in cases of intense infection when space has become limited, the number may be only four.
After a number of generations of merozoites have been formed, a limit is reached both to the multiplicative capacity of the parasite and to the power of the bird to provide the invader with food. Consequently, resistant forms of the parasite are necessary, and the trophozoites begin to show sexual differentiation instead of forming schizonts, that is, gametogony commences.
Certain trophozoites store food and become large and granular. These are macrogametocytes (fig. 69, I, ♀). The microgametocytes (fig. 69, I, ♂) are smaller and far less granular. The macrogametocyte continues to grow, and becomes loaded with chromatoid and plastinoid granules (fig. 69, J, ♀), while the microgametocyte has its nucleus divide to form a number of bent, rod-like portions (fig. 69, J, ♂). The macrogametocyte gives rise to a single macrogamete, which forms a cyst wall for itself, leaving a thin spot (micropyle) for the entry of the male (fig 69, K, ♀). The microgametocyte gives rise to numerous small, biflagellate microgametes (fig. 69, K, ♂) around a large, central residual mass, from which they ultimately break free, and swim away. When a macrogamete is reached, the microgamete enters through the micropyle (fig. 69, L)—which then closes, thus excluding the other males—and applies itself to the female nucleus (fig. 69, M). Nuclear fusion occurs, the oöcyst (encysted zygote) being thus produced. Sporogony then ensues. The oöcyst (fig. 69, N) at first has its contents completely filling it. They then concentrate into a central spherical mass (fig. 69, O) which gradually becomes tetranucleate (fig. 69, P). Cytoplasm collects around each nucleus, and four sporoblasts are thus formed (fig. 69, Q). Each sporoblast becomes oval (fig. 69, R) and produces a sporocyst. Ultimately two sporozoites are formed in each sporocyst or spore, at first lying tête-bêche (fig. 69, S), but finally twisting to assume the position most convenient for emergence (fig. 69, T) when they reach a new host. The period of the life-cycle of Eimeria avium (as well as the details of the life-cycle) was determined by Fantham to be from eight to ten days, of which period schizogony occupies four to five days.
The method of infection175 is contaminative, by way of food or drink. Young birds are especially susceptible to infection. Certain birds, particularly older ones, may act as reservoirs of oöcysts, being continuously infected themselves, without showing any marked ill effects from the parasite, but being highly infectious to other birds. Much moisture retards the development of sporocysts considerably. The duration of vitality of the infective oöcysts has been determined experimentally to extend well over two years, and in certain cases longer. Eimeria avium is the causal agent of “white diarrhœa” or “white scour” in fowls, and of “blackhead” in turkeys.
Eimeria avium of birds and E. stiedæ of rabbits closely resemble one another, but are not the same parasite, for E. avium is not infective to rabbits, nor E. stiedæ to poultry.
Eimeria stiedæ, Lindemann, 1865.
Syn.: Monocystis stiedæ, Lindemann, 1865; Psorospermium cuniculi, Rivolta, 1878; Cytospermium hominis, Rivolta, 1878; Coccidium oviforme, Leuckart, 1879; Coccidium perforans, Leuckart, 1879; Coccidium cuniculi.
Eimeria stiedæ is parasitic in the gut epithelium (fig. 70), liver, and epithelium of the bile ducts of rabbits, and is usually considered to be the parasite very occasionally found in man. The life-cycle resembles that of Eimeria avium in its general outlines (see fig. 69) and therefore will not be detailed in full here. The oöcysts (fig. 71) are large, elongate-oval, greenish in fresh preparations and vary in size from 24 µ to 49 µ long and 12·8 µ to 28 µ broad, the gut forms being usually smaller than those occurring in the liver, owing to the more confined space in which they are formed. Formerly, the parasites in the liver were described under the name of Coccidium oviforme, while those from the intestine were termed Coccidium perforans. This distinction has now broken down.
Fig. 73.—So-called swarm cysts (endogenous sporulation or schizogony) of the Coccidium of the rabbit. The daughter forms are called merozoites. (After R. Pfeiffer.)
The oöcysts176 are thick-walled, somewhat flattened at one pole, where a large micropyle is present. Four egg-shaped spores (sporocysts) are formed within, each about 12 µ to 15 µ long and 7 µ broad (fig. 72). The oöcysts are voided with the fæces. Sporogony takes, in nature, about three days in the excrement. Fæcal contamination of the food of rabbits results, and coccidian oöcysts are swallowed. Under the influence of the pancreatic juice of a new host, the sporozoites (fig. 72, a—c) are liberated from the spores and proceed to attack the epithelium and multiply within it, as in the case of Eimeria avium. From the gut, infection spreads to the liver, where multiplication of the parasite goes on actively, resulting in the formation of the whitish coccidial nodules, which may be very conspicuous (fig. 74). Proliferation of the connective tissue may occur around the coccidial nodules, which then contain large numbers of oöcysts in various stages of development. It is said that the oöcysts in the older nodules do not seem to be capable of further development. Schizogony (fig. 73) and gametogony in all stages can be found in both liver and gut.
Young rabbits often die of intestinal coccidiosis before infection of the liver occurs. The repeated schizogony of Eimeria stiedæ in the gut is sufficient to cause death.
The disease of cattle popularly known as “red dysentery” is also ascribed to the action of Eimeria stiedæ. The fæces of infected cattle show blood clots of various sizes and in severe cases watery diarrhœa is present. Acute cases end fatally in about two days. Numerous oöcysts, considered to be those of Eimeria stiedæ, occur in the fæces, and there is a heavy infection of the gut, especially the large intestine and rectum, all stages of the parasite being found in the epithelium. It is suspected that cattle contract the disease by feeding on fresh grass contaminated with oöcysts. The disease is recorded from Switzerland and from East Africa.
As before mentioned, Eimeria stiedæ is considered to be the organism found in a few cases in man, possibly acquired by eating the insufficiently cooked livers of diseased rabbits. These cases may now be described.
(a) Human Hepatic Coccidiosis.
(1) Gubler’s Case. A stone-breaker, aged 45, was admitted to a Paris hospital suffering from digestive disturbances and severe anæmia. On examination the liver was found to be enlarged and presented a prominent swelling, which was regarded as being due to Echinococcus. At the autopsy of the man, who succumbed to intercurrent peritonitis, twenty cysts were found averaging 2 to 3 cm. in diameter, and one measuring 12 to 15 cm. The caseous contents consisted of detritus, pus corpuscles, and oval-shelled formations, which were considered to be Distoma eggs, but which, in accordance with Leuckart’s conjecture, proved to be Coccidia.177
(2) Dressler’s Case (Prague). Relates to three cysts, varying from the size of a hemp-seed to that of a pea, and containing Coccidia, found in a man’s liver.178
(3) Sattler’s Case (Vienna). Coccidia were in this case observed in the dilated biliary duct of a human liver.179
(4) Perls’ Case (Giessen). Perls discovered Coccidia in an old preparation of Sömmering’s agglomerations.180
(5) Silcock’s Case (London).181 The patient, aged 50, who had fallen ill with serious symptoms, exhibited fever, enlarged liver and spleen, and had a dry, coated tongue. At the autopsy numerous caseous centres, mostly immediately beneath the surface, were found, while the contiguous parts of the liver were inflamed. Microscopical examination demonstrated numerous Coccidia in the hepatic cells as well as in the epithelium of the biliary ducts. A deposit of Coccidia was likewise found in the spleen, which the parasites had probably reached by means of the blood-stream.182
(b) Human Intestinal Coccidiosis.
In two cadavers at the Pathological Institute in Berlin, Eimer183 found the epithelium of the intestine permeated by Coccidia. Railliet and Lucet’s case may be traced back to intestinal Coccidia, which were found in the fæces of a woman and her child, who had both suffered for some time from chronic diarrhœa.184 In other cases (Grassi, Rivolta), where only the existence of Coccidia in the fæces was known, it is doubtful whether the parasites originated in the intestine or in the liver.
(c) Doubtful Cases.
To these belong Virchow’s case185 where, in the liver of an elderly woman, a thick walled tumour measuring 9 to 11 mm. was found. Among the contents of this tumour there were oval formations 56 µ long, surrounded by two membranes and enclosing a number of round substances. Virchow considered these foreign bodies to be eggs of pentastomes in various stages of development, others consider them to be Coccidia.
The Coccidia which Podwyssotzki claims to have seen in the liver of a man, not only in the liver cells, but also in the nuclei, are also problematic.186 The parasite was called Caryophagus hominis.
Again, other explanations can be given to an observation by Thomas, on the occurrence of Coccidium oviforme in a cerebral tumour of a woman aged 40. The growth was as large as a pea and surrounded by a bony substance.187
Genus. Isospora, Aimé Schneider, 1881.
Syn.: Diplospora, Labbé, 1893.
Belonging to the section Disporea, that is, forming only two spores, each with four sporozoites.
Isospora bigemina, Stiles, 1891.
Syn.: “Cytospermium villorum intestinalium canis et felis,” Rivolta, 1874; “Coccidium Rivolta,” Grassi, 1882; Coccidium bigeminum, Stiles, 1891.
This parasite lives in the intestinal villi of dogs, cats, and the polecat (Mustela putorius, L.). According to Stiles,188 the oöcyst divides into two equal ellipsoidal portions or sporoblasts which become spores and then each forms four sporozoites. The oöcysts of this species vary from 22 µ to 40 µ in length and from 19 µ to 28 µ in breadth. Each spore is 10 µ to 18 µ long and contains four sporozoites. The parasites live and multiply, not only in the gut epithelium, but also in the connective tissue of the intestinal submucosa. Wasielewski has seen merozoites in the gut of the cat.
Isospora bigemina (fig. 75) appears to occur also in man, for Virchow published a case which was communicated to him by Kjellberg, and attributed the illness to this parasite.189 Possibly also it would be more correct to ascribe the observation of Railliet and Lucet, which is mentioned under “Human Intestinal Coccidiosis,” p. 148, to this species, as the Coccidia in that case were distinguished by their diminutive size (length 15 µ, breadth 10 µ). The case communicated by Grunow may also possibly refer to Isospora bigemina.190 Roundish or oval structures of 6 µ to 13 µ in diameter occurred in the mucous membrane of the gut and in the fæces of a case of enteritis.
Fig. 75.—Isospora bigemina, Stiles (from the intestine of a dog). a, Piece of an intestinal villus beset with Isospora, slightly enlarged; b, Isospora bigemina (15 µ in diameter), shortly before division; c, divided; d, each portion encysted forming two spores; e, four sporozoites in each part, on the left seen in optical section, together with a residual body—highly magnified. (After Stiles.)
Doubtful Species.
In literature many other statements are found as to the occurrence of Coccidia-like organisms in different diseases of man. In some of the cases the parasites proved to be fungi. This was the case with the parasites of a severe skin disease of man, formerly called Coccidioides immitis and Coccidioides pyogenes. Other statements are founded on misapprehensions, or are still much disputed. If reference is here made to “Eimeria hominis,” R. Blanchard, 1895, this is done on the authority of the investigator mentioned. The structures in question are nucleated spindle-shaped bodies of very different lengths (18 µ to 100 µ), which either occurred isolated or were enclosed in large globular or oval cysts, alone or with a larger tuberculated body (“residual body”). These formations were found by J. Künstler and A. Pitres in the pleural exudation removed from a man by tapping. The man was employed on the ships plying between Bordeaux and the Senegal River.
Blanchard looks upon the fusiform bodies as merozoites and the cysts as schizonts of a Coccidium. On the other hand, Moniez declares the spindle bodies to be the ova and the supposed residual bodies to be “floating ovaries” of an Echinorhynchus.
Severi’s “monocystid Gregarines,” which were taken from the lung tissue of a still-born child, are also quite problematical.
No less doubtful are the bodies which Perroncito calls Coccidium jalinum, and which he found in severe diseases of the intestine in human beings, pigs, and guinea-pigs; Borini also reported another case.
Order. Hæmosporidia, Danilewsky emend. Schaudinn.
The Hæmosporidia are a group of blood parasites, comprising forms differing greatly among themselves. Some of the forms need much further investigation. However, there are certain true Hæmosporidia which present close affinities with the Coccidia, leading Doflein to use the term Coccidiomorpha for the two orders conjoined.
The Hæmosporidia present the following general characteristics:—
(1) They are parasites of either red or white blood corpuscles of vertebrates during one period of their life-history.
(2) They exhibit alternation of generations—asexual phases or schizogony alternating with sexual phases or sporogony—as do the Coccidia.
(3) There is also an alternation of hosts in those cases which have so far been completely investigated. The schizogony occurs in the blood or internal organs of some vertebrates while the sporogony occurs in an invertebrate, such as a blood-sucking arthropod or leech.
(4) Unlike the Coccidia, resistant spores in sporocysts are not generally produced, such protective phases in the life-cycle being unnecessary, as the Hæmosporidia are contained within either the vertebrate or invertebrate host during the whole of their life.
The Hæmosporidia may be considered for convenience under five main types:—
(1) The Plasmodium or Hæmamœba type. This includes the malarial parasites of man and of birds. The asexual multiplicative or schizogonic phases occur inside red blood corpuscles and are amœboid. They produce distinctive, darkish pigment termed melanin or hæmozoin. Infected blood drawn and cooled on a slide may exhibit “exflagellation” of the male gametocytes, i.e., the formation of filamentous male gametes. The invertebrate host is a mosquito. The malarial parasites of man are discussed at length on p. 155. Similar pigmented hæmamœboid parasites have been described in antelopes, dogs, and other mammals, and even reptiles.
(2) The Halteridium type. The trophozoite stage inside the red blood corpuscle is halter-shaped. Pigment is produced, especially near the ends of the organism. The parasites occur in the blood of birds. The invertebrate host of H. columbæ of pigeons in Europe, Africa, Brazil and India, is a hippoboscid fly, belonging to the genus Lynchia.
Halteridium parasites are common in the blood of passerine birds, such as pigeons, finches, stone owls, Java sparrows, parrots, etc. The Halteridium embraces or grows around the nucleus of the host red cell without displacing the nucleus. Young forms and multiplicative stages of H. columbæ have been found in leucocytes in the lungs of the pigeon (fig. 76, 8-12). Male and female forms (gametocytes) are seen in the blood (fig. 76, 3a, 3b). The cytoplasm of the male gametocytes is pale-staining and the nucleus is elongate, while the cytoplasm of the females is darker and the nucleus is smaller and round. Formation of male gametes from male gametocytes (the so-called process of “exflagellation”) may occur on a slide of drawn infected blood, also fertilization, and formation of the oökinete, as first seen by MacCallum. The correct generic name for Halteridia is, apparently, Hæmoproteus. Wasielewski (1913), working on H. danilewskyi (var. falconis), in kestrels, finds that the halteridium may be pathogenic to nestlings. The cycle of H. noctuæ described by Schaudinn (1904) lacks confirmation. The account of the life-cycle of H. columbæ given by Aragão (1908) is illustrated in fig. 76. It agrees with the work of Sergent (1906–7) and Gonder (1915). Mrs. Adie (1915) states that the cycle in Lynchia is like that of a Plasmodium.
Fig. 76.—Hæmoproteus (Halteridium) columbæ. Life-cycle diagram: 1, 2, stages in red blood corpuscle of bird; 3, 4, gametocytes (3a ♂, 3b ♀); 5a, formation of microgametes; 6, fertilization (in fly’s gut); 7, oökinete; 8–12, stages in mononuclear leucocytes in lungs. (After Aragão.)
(3) The Leucocytozoön type. The trophozoites and gametocytes occur within mononuclear leucocytes and young red cells (erythroblasts) in the blood of birds. Laveran and França consider that the Leucocytozoa occur in erythrocytes. The host cells are often greatly altered by the parasites, becoming hypertrophied and the ends usually drawn into horn-like processes (fig. 77), though some remain rounded. Leucocytozoa are limited to birds, and very rarely produce pigment. Male and female forms (gametocytes) are distinguishable in the blood (fig. 77), and the formation of male gametes (“exflagellation”) may occur in drawn blood.
Fig. 77.—Leucocytozoön lovati. a, Male parasite (microgametocyte), within host cell, whose ends are drawn out; b, female parasite (macrogametocyte) from blood of grouse. × 1,800. (After Fantham.)
The Leucocytozoa were first seen by Danilewsky in 1884. They are usually oval or spherical. It is not easy sometimes to distinguish the altered host cell from the parasite, as the nucleus of the former is pushed to one side by the leucocytozoön. The cytoplasm of the female parasite stains deeply, and the nucleus is rather small, containing a karyosome. In the male the cytoplasm stains lightly and the nucleus is larger, with a loose, granular structure.
Many species of Leucocytozoa are recorded, but schizogony has only been described by Fantham (1910)191 in L. lovati in the spleen of the grouse (Lagopus scoticus), and by Moldovan192 (1913) in L. ziemanni in the internal organs of screech-owls.
M. and A. Leger193 (1914) propose to classify Leucocytozoa, provisionally, according as the host cells are fusiform or rounded.
(4) The Hæmogregarina type. Included herein are many parasites of red blood corpuscles, with a few (the leucocytogregarines) parasitic in the white cells of certain mammals and a few birds. They are not amœboid but gregarine-like, vermicular or sausage-shaped (fig. 78). They do not produce pigment. They are widely distributed among the vertebrata, but are most numerous in cold-blooded vertebrates (fishes, amphibia and reptiles). The hæmogregarines of aquatic hosts are transmitted by leeches, those of terrestrial hosts by arthropods.
The nucleus of hæmogregarines is usually near the middle of the parasite, but may be situated nearer one end. The body of the parasite may be lodged in a capsule (“cytocyst”). There is much variation in size and appearance among hæmogregarines. Some are small (Lankesterella); some attack the nucleus of the host cell (Karyolysus); others have full grown vermicules larger than the containing host corpuscle, and so the hæmogregarines bend on themselves in the form of U (fig. 78, b). Schizogony often occurs in the internal organs of the host, sometimes in the circulating blood.
The hæmogregarines occurring in the white cells (mononuclears or polymorphonuclears) of mammals have been referred to a separate genus, Leucocytogregarina (Porter) or Hepatozoön (Miller). Such leucocytogregarines are known in the dog (fig. 79), rat, mouse, palm-squirrel, rabbit, cat, etc. Schizogony of these forms occurs in the internal organs, such as the liver, lung and bone-marrow of the hosts. They are apparently transmitted by ectoparasitic arthropods, such as ticks, mites, and lice.
Fig. 78.—Hæmogregarines from lizards, a, H. schaudinni, var. africana, from Lacerta ocellata; b, H. nobrei from Lacerta muralis; c, H. marceaui in cytocyst, from Lacerta muralis. (After França.)
A few hæmogregarines are known to be parasitic in the red blood corpuscles of mammals. Such are H. gerbilli in the Indian field rat, Gerbillus indicus; H. balfouri (jaculi) in the jerboa, Jaculus jaculus, and a few species briefly described from marsupials. These parasites do not form pigment.
Strict leucocytic gregarines have been described from a few birds by Aragão and by Todd.
The sporogony of hæmogregarines is only known in a few cases, and in those affinity with the Coccidia is exhibited. In fact, the Hæmogregarines are now classified by some authors with the Coccidia.
(5) The Babesia or Piroplasma type. These are small parasites of red blood corpuscles of mammals. They do not produce pigment. They are pear-shaped, round or amœboid in Babesia, bacilliform and oval in other forms referred to this group. Piroplasms are transmitted by ticks. These parasites are described at length on p. 172.
Fig. 79.—Leucocytogregarina canis. Life-cycle diagram. Constructed from drawings by Christophers. (After Castellani and Chalmers.) Schizogony occurs in the bone-marrow. The parasite is transmitted from dog to dog by the tick, Rhipicephalus sanguineus, development in which, so far as known, is shown on the right.
THE MALARIAL PARASITES OF MAN.
Malaria, otherwise known as febris intermittens, chill-fever, ague, marsh fever, paludism, etc., is the name given to a disease of man, which begins with fever. It has been known since ancient times and is distributed over almost all the world, although very unevenly, but does not occur in waterless deserts and the Polar regions. In many places, especially in the civilized countries of Central Europe, the disease is extinct or occurs only sporadically, and large tracts of land have become free from malaria.
The rhythmical course of the fever is characteristic. It begins apparently suddenly with chilliness or typical shivering, whilst the temperature of the body rises, the pulse becomes low and tense and the number of beats of the pulse increases considerably. After half to two hours the heat stage begins. The patient himself feels the rise of his temperature (shown by feeling of heat, dry tongue, headache, thirst). The temperature may reach 41°C or more. At the same time there is sensitiveness in the region of the spleen and enlargement of that organ. After four to six hours an improvement takes place, and with profuse perspiration the body temperature falls rapidly, not often below normal. After the attack the patient feels languid, but otherwise well until certain prodromal symptoms (heaviness in the body, headache) which were not noticed at first, denote the approach of another attack of fever, which proceeds in the same way.
The intervals between the attacks are of varying length which permit of a distinction in the kinds of fever. If the attacks intermit one day, occurring on the first, third and fifth days of the illness and always at the same time of day, it is termed febris tertiana; if two days occur between fever days, it is called febris quartana. In the case of the fever recurring daily, later writers speak of typical febris quotidiana. But a quotidian fever may arise when two tertian fevers differing by about twenty-four hours exist at the same time (febris tertiana duplex). The patient has a daily attack, but the fever of the first, third and fifth days differs in some point (hour of occurrence, height of temperature, duration of cold or hot stage) from the fever of the second, fourth and sixth days. Similarly, two or three quartan fevers which differ by about twenty-four hours each may be observed together (febris quartana duplex or triplex); in the latter case the result is also a quotidian fever.
Two kinds of tertian fever are differentiated—a milder form occurring especially in the spring (spring tertian fever), and a more severe form appearing in the summer and autumn in warmer districts, especially in the tropics (summer or autumn fever, febris æstivo-autumnalis, febris tropica, febris perniciosa). The latter often becomes a quotidian fever.
All the afore-mentioned infections are termed acute. They are distinguished from the very different chronic malarial infection by the frequent occurrence of relapses, which finally lead to changes of some organs and particularly of the blood. The relapses are then generally marked by an irregular course of fever.
The term masked malaria is used when any disturbance of the state of health of a periodic character shows itself and disappears after treatment with quinine.194 Generally it is a question of neuralgia.