Sporozoite

“ 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) . ”

“ These spores, or merozoites, enter new blood cells and repeat the process (auto-infection) . When taken into the stomach of the mosquito Anopheles, the parasites become much larger, some develop male gametes (o, p, q) on the Polymitus form {p) ; others, female gametes (r—u) . These conjugate (v) in the stomach of Anopheles, and the copula (w) penetrates the epithelial lining of the stomach and ultimately lies suspended in the body cavity (x—zz) . When mature, the parasite forms spores (A) , which form, in turn, naked sporozoites (B) . ”

“ If a mosquito whose salivary glands contain malarial sporozoites bites a man, the sporozoites are introduced into the blood, penetrate the red corpuscles, and multiply. After eight to ten days their progeny can be seen as malaria parasites of the type corresponding to those of the man on whom the infecting mosquito had originally fed. Schaudinn, by diluting blood with blister serum and introducing into the mixture the salivary glands of a malaria-infected mosquito, was enabled to witness the entrance of the sporozoites into the red corpuscles. ”

“ Rowley-Lawson is of the opinion that the greater red cell destruction than would be represented by percentage of cells showing parasites is explained by parasites migrating from cell to cell so that many red cells may be destroyed by a single parasite.
4. Transmission to larvae.—There has been an idea that sporozoites might enter the ovaries and ova as well as the salivary glands so that a second generation of mosquitoes might transmit malaria. There is no proof that such a method is ever operative. ”

“ While, however, it is easy enough sharply to separate off all Haemosporidia from other Ectospora, it is a very difficult matter to define their limits on the former side. Two principal criteria which a doubtful haemal parasite might very well be required to satisfy in order to be considered as a Haemosporidian rather than a Haemoflagellate are (a) the occurrence of schizogony during the “corpuscular” phase in the Vertebrate host, and (b) the formation of many germs (“sporozoites”) from the zygote ”

“ The valves are usually prolonged into processes or appendages, whose form and arrangement characterize the genus; but in Sphaeractinomyxon the spore is spherical and lacks processes. The sporoplasm may be either a plasmodial mass, with numerous nuclei, or may form a certain number of uninuclear sporozoites. A remarkable feature in the development of the spore is that the germinal tissue (sporoplasm) arises separate from and outside the cellules which give rise to the spore-wall; later, when the envelopes are nearly developed, the sporoplasm penetrates into the spore. ”

“ 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. ”

“ Gregarines in which the sporozoites are naked) constitute in reality nothing more or less than a schizogonous generation of these Cephalopodan parasites, which have thus an alternation of true hosts. The ripe sporocysts from the Cephalopod are eaten by a particular crab (e.g. Portunus or Inachus, according to the parasite) , the sporozoites are liberated and traverse the mucous membrane of the intestine, coming to rest in the surrounding lymphatic layer. Here a large “cyst” is formed, projecting into the body-cavity, the contents of which give rise to a great number of merozoites. ”

“ The flea, for example, and other insects that prey on man must be examined with this end in view. There is no reason to believe that the sporozoites can be liberated in water, or suspended in the dust of the air, and live, for, of all Sporozoa, the blood-infesting forms are not protected against an external life. Thus we have seen that the sporozoites of the gregarine or of Coccidium are incased in a firm, calcareous shell, which protects them from drying and from other dangers that might be encountered. With the malaria-organism there is no such coating ”

“ Around this some of the cytoplasm condenses, the rest forming a residuum. The sporoblast or gamete thus formed is completely isogamous and normally conjugates with the like one from the other associate, when a single zygote results which becomes a spore containing eight sporozoites, in the ordinary manner. Sometimes, however, the septum between the two halves of the cyst does not break down, in which case parthenogenesis occurs, each sporoblast developing by itself into a small spore. ”

“ It is certain that the number of nuclei increases with simultaneous decrease in size. They soon appear on the surface of the strands or sporoblasts, surround themselves with some cytoplasm and then elongate (fig. 84) . In this manner the sporozoites are formed and break away from the unused remains of the cytoplasmic strands of the sporoblasts (fig. 80, 26) . The number of the sporozoites in an oöcyst varies from several hundreds to ten thousand.
Fig. 84.—Four different sporulation stages of malarial parasites from Anopheles maculipennis, much magnified. a-c, of the malignant tertian parasite ”

“ In the meantime the female sporont, after giving off a reduction nucleus, is ready for fertilization by the microgamete. The female cell (zygote) is capable of independent movement, and (now termed an oökinete) bores its way through the lining epithelium of the mosquito's stomach, there encysts between the epithelium and the limiting membrane, and becomes an oöcyst. The original nucleus now breaks up into sporoblasts, which in turn break up into sporozoites. ”

“ U-W, maturation of oosphere; X, fertilisation; Y, zygote. a, Zygote enlarging in gut of Mosquito; b-e, passing into the coelom; f, the contents segmented into naked spores; g, the spores forming sickle-germs or sporozoites; h, sporozoites passing into the salivary glands. (From Calkins's Protozoa, after Ross and Fielding Ould.)
The nucleus of the schizont now divides repeatedly, and then the schizont segments into a flat brood of germs (merozoites) , relatively few in the parasite of quartan fever (Haemamoeba malariae, Fig. 35, E-G) , many in that of tertian (H. vivax, Fig. 35, M) . ”

“ 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. ”

“ Order 2.—Coccidiidea. Body of uniform spherical or oval shape: they lead an intracellular life, but are not freely motile in cavities of the body. Fertilization is anisogamous; the spores have coats or shells (sporocysts) , and usually contain several sporozoites. Exhibit alternation of generations.
Order 3.—Hæmosporidia. Parasites of the blood corpuscles of vertebrate animals; they exhibit amœboid movement; fertilization is anisogamous; many present alternation of generations and hosts; spores naked. ”

“ These insects inject a parasitic form known as sporozoites into people, where they replicate briefly inside liver cells. The liver cells then release merozoites (another parasitic form) , which invade red blood cells. ”

“ 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 ”

“ As the name implies, the spores of the Haplosporidia are simple, without polar capsules, and are uninucleate. In some genera, e.g., Haplosporidium, Urosporidium (fig. 111) there is a spore-coat or sporocyst which may be elongate or spiny. The developmental cycle of a Haplosporidian, such as Haplosporidium or Bertramia, begins with a small, uninucleate cell, often rounded, possessing a cell membrane that may be prolonged into processes. Growth takes place, coupled with an increase in the number of nuclei, so that a multinucleate trophozoite is produced. ”

“ The disease is contracted from spores present in the soil, which enter the root. The parasite develops within the living cells of the plant, forming a glairy mass of protoplasm known as the plasmodium, the form of which alters from time to time. The cells which have been attacked increase enormously in size and the disease spreads from cell to cell. Ultimately the plasmodium becomes resolved into numerous minute round spores which, on the decay of the root, are set free in the soil. A preventive is quicklime, the application of which destroys the spores in the soil. ”

“ A number of diseases in man and other animals are due to the presence of these Sporozoans, for they are all parasitic. Few if any animals are exempt from their attacks. They even attack other minute Protozoa. One hundred and fifty-seven species have been recorded as attacking insects, one hundred species attack birds, fifty-two reptiles, eighty crustaceans, twenty-two fish, and so through the list. Ten have been recorded as attacking man. In some instances the parasite is always present in the host and some hosts may harbor several different species of Sporozoa. ”

“ Certain of the cysts have been found in a ruptured condition, whereby the spores have been liberated into the surrounding tissue. It is almost certain that the spores serve for the auto-infection of the host, for though the tumours of Rhinosporidium seemed to have been removed entirely, it has been found that they recur, some minute fragment of the parasite having probably been left behind. The method whereby the parasite reaches new hosts has not yet been determined, and it would be of interest if its life-history could be more fully investigated. ”

“ In addition, the great majority have also another method of reproduction, for increasing the number of the parasites in any individual host; this is distinguished as multiplicative or endogenous reproduction, from the propagative or exogenous method (by means of the resistant spores) , which serves for the infection of fresh hosts and secures the dissemination and survival of the species. Further, most if not all forms of Sporozoa undergo sexual conjugation at some period or other of the life-cycle. ”

“ During the time that the parasite is feeding and growing it is also giving off waste products, as all living forms do in the process of metabolism, but as the parasite is completely inclosed in the corpuscle wall these waste products cannot escape until the wall bursts open. After about forty hours if the parasite is vivax or about sixty-five hours if it is malariæ it becomes immobile, the nucleus divides again and again and the protoplasm collects around these nuclei, forming a number of small cells or spores, as they are called. ”

“ 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. ”

“ When free in the field of the microscope, spores must be distinguished from fat cells, micrococci, starch cells, some kinds of ova, yeast cells, and other like objects. Spores are detected frequently by their resistance to ordinary stains and the necessity of colouring them by special staining methods. When, however, a spore has taken on the desired colour, it retains it with tenacity. In addition to their shape, size, thickened capsule, and staining characteristics, spores also resist desiccation and heat in a much higher degree than bacilli not bearing spores. ”

“ Nos. 1, 2, 3, 4, show the growth and the changing shape of the parasite within the blood-corpuscle; Nos. 3, 4, etc., show the aggregation of the pigment, melanin, in the parasite; No. 5 is a sporocyte, which in Nos. 6, 7, and 8, shows the several stages of sporulation; No. 9 shows the spores derived from a single sporocyte, escaped from the blood-corpuscle and free in the blood-plasm, ready to infect new corpuscles; No. 10 is a male gametocyte, removed from the body of man, and either in the stomach of Anopheles or on a microscope-slide, forming there flagella or spermatozoa, a, Parasite ”