In this article we will discuss about Eimeria Schubergi:- 1. Habit and Habitat of Eimeria Schubergi 2. Structure of Eimeria Schubergi 3. Nutrition 4. Life Cycle 5. Pathogenicity.
Habit and Habitat of Eimeria Schubergi:
Eimeria schubergi is an intracellular parasite in the epithelial cells of alimentary canal of centipede, Eithobius forficatus. The greater part of the life cycle of Eimeria schubergi is spent in the host and a part in open.
Structure of Eimeria Schubergi:
The full grown trophozoite is small, spherical and simple in structure. The cytoplasm is granular and contains a single nucleus. The nucleus of full grown trophozoite also contains a small endosome in its centre. Mouth, gullet, anus, contractile and locomotory organelles are absent due to parasitic mode of life.
Nutrition of Eimeria Schubergi:
Nutrition is saprozoic. It feeds mainly on the dissolved food of the host by absorbing it, i.e., osmotrophy. It also subsists on the contents of the cell of the host in which it is living.
Life Cycle of Eimeria Schubergi:
Eimeria schubergi is monogenetic, i.e., its life cycle is completed in one host only; the host being centipede, Lithobius forficatus. Its life cycle may be studied into asexual phase including schizogony, sexual phase including gamogony and the phase of spore formation, i.e., sporogony.
From all these three phases, first two take place either in the intestinal wall or in the intestinal lumen but the third phase takes place outside the body of the centipede in open.
Asexual Phase:
Schizogony:
The parasites, enclosed in spherical capsules, oocysts, find their way into the intestine of a healthy centipede, which are accidentally swallowed along with the food. In the intestine, the oocysts are digested. Each oocyst releases eight motile, falciform sporozoites.
The sporozoites are sickle-shaped and tapering at both ends. Each sporozoite penetrates into an epithelial cell of the alimentary canal of the host. It grows into a large, round adult called trophozoite.
The trophozoite becomes full grown in about 24 hours and it is then called a schizont. The schizont is characterised by the large vesicular nucleus containing an endosome and by the absence of reserve food material in the cytoplasm. The schizont undergoes multiple fission and the fission of the schizont is known as schizogony. The nucleus of the schizont divides into a number of nuclei which migrate to the surface.
Each nucleus gets surrounded by some cytoplasm, thus, a large number of club-shaped schizoites or merozoites are formed. The portion of the cytoplasm in the centre of schizont is termed the residual cytoplasm. By this time the host cell becomes very weak because its contents have been used up by the parasite.
The membrane of the host cell ruptures and the merozoites escape from the epithelial cell and become free in the lumen of the gut.
The merozoites resemble with the sporozoites in form, structure and movement but differ from them in having an endosome and slightly shorter in size. The merozoites penetrate fresh epithelial cells, grow into trophozoites and repeat schizogony. This goes on for some generations.
Schizogony is repeated till the greater part of the intestinal epithelium is destroyed and the parasites experience increasing difficulty in procuring proper nourishment.
Sexual Phase:
Gamogony:
After several repeated cycles of asexual proliferation, some merozoites instead of forming trophozoites enter the fresh intestinal epithelial cells. After entering the epithelial cells, merozoites begin to grow slowly and differentiate to form two kinds of cells called microgametocytes or male gametocytes and macro-gametocytes or female gametocytes.
A male gametocyte is spherical having clear cytoplasm, while the female gemetocyte is bean-shaped having its cytoplasm crowded with darkly staining refractile granules. Male gametocyte divides to form numerous narrow, biflagellate microgametes (also called merogametes) or male gametes.
The female gametocyte extrudes chromatin from its nucleus and forms single macrogamete (also called hologamete) or female gamete. The male and female gametes escape into the lumen of the gut where one male gamete fertilises the female gamete to form a zygote by syngamy or anisogamy. In fertilisation, the flagella of the male gamete are discarded.
The zygote soon gets enclosed in a tough resistant cyst to form a round oocyst. As a rule, the oocyst does not develop further in the lumen of the intestine of the centipede and the young oocyst passes to the exterior with the faeces. The oocysts are very resistant and can survive highly adverse conditions.
Phase of Spore Formation:
Sporogony:
The oocyst does not increase in size. The zygote nucleus divides twice to form four ovoid sporoblasts. The first division of the zygote nucleus is said to be the reduction division. Some cytoplasm remains unused during divisions of the zygote nucleus and is called cystal residue. Each sporoblast secretes a chitinous secondary cyst, the sporocyst consisting of two boat- shaped valves joined together longitudinally.
The oocyst is known as tetrasporous because it contains four sporocysts. The nucleus and cytoplasm of each sporoblast divide to form two sporozoites within the sporocyst. Here also some cytoplasm remains unused which lies between two sporozoites and is called sporal residue. The sporocysts are known as dizoic because each contains two sporozoites. A mature oocyst contains four sporocysts each having two sporozoites.
Thus, there is an additional generation in sporogony by which each sporocyst gives rise to two sporozoites.
The oocyst containing four sporocysts and each sporocyst having two sporozoites becomes infective for the host. If the oocyst is swallowed by another centipede, the cyst walls are dissolved and the valves of the sporocysts split open and eight sporozoites escape and they penetrate the epithelial cells of the intestine and start multiplication by schizogony.
Alternation of Generation in Eimeria:
In the life cycle of Eimeria schubergi, the schizogonic and sporogonic phases constitute the asexual generation as in these phases reproduction occurs by an asexual method of multiple fission. On the other hand gamogony represents the sexual generation as it involves the formation of male and female gametes and their subsequent fusion or fertilisation.
The sexual generation is always followed by the asexual generation. The phenomenon in which the sexual and asexual generations are followed by each other regularly is called the alternation of generations.
Pathogenicity of Eimeria Schubergi:
The infection of Eimeria schubergi causes damage to the epithelial cells of the intestine. But, certain species of Eimeria are very harmful to their hosts like cattle, chicken, pig, etc., and, thus, it renders an economic damage to man. The pathogenicity of the different species of Eimeria varies greatly.