Term Paper on Eimeria | Protozoa | Microorganisms | Zoology

Here is a term paper on ‘Eimeria’. Find paragraphs, long and short term papers on ‘Eimeria’ especially written for college and medical students.  

Term Paper # 1. Habits and Habitat of Eimeria:

Eimeria, belonging to sub-class Coccidia of sub-phylum Sporozoa, is a parasite living in the cells of digestive canal of many invertebrates and vertebrates. It causes a fatal disease known as coccidiosis. Eimeria has many species like E. tenella in the caecum of chicken E. mitis in the anterior part of the ileum of adult birds, E. bovis in the intestine of catties, E. canis in the small intestine of dog E. stiedae in the bile duct of rabbit and E. schubergi in the alimentary canal of centipede arthropods.

It is an intracellular parasite in the epithelial cells of alimentary canal of centipede, Lithobius forficatus. The greater part of the life cycle of Eimeria schubergi is spent in the host and a part in open.

The two occidian genera, Eimeria and Isospora, are economically important as they cause a severe disease condition, known as coccidiosis, in their respective hosts. Two species of Eimeria cause heavy losses to the poultry industry in India. One of them, E. tenella, affects the caeca of chicken and causes caecal coccidiosis.

Another species, E. mitis, attacks the anterior part of the ileum of adult birds. The best known species, E. stiedae, causes “liver coccidiosis” of young rabbits by attacking the lining cells of their bile ducts. Other important mammalian species are E. bovis in the intestine of the cattle and E. canis in the small intestine of dog E. schubergi occurs in the centipede Lithobius.

In case of Eimeria, nutrition is saprozoic. It feeds mainly on the dissolved food of the host by absorbing it. It also subsists on the contents of the cell of the host in which it is living.

Term Paper # 2. Structure of Eimeria:

The adult stage of the parasite is known as trophozoite which is to smaller, spherical and simpler in structure. The outermost covering is called pellicle which porous and equivalent to plasma membrane. It endorse small amount of cytoplasm which is granular and contains a small single nucleus in the center of it. The nucleus contains a small endosome within in it apart from the chromatin material. Being endoparasite, Eimeria does not contain any mouth, gut, anus, contractile vacuole or locomotory organelle etc.

Eimeria is sporozoic, and feeds on the dissolved food of its host.

Term Paper # 3. Life History of Eimeria:

Eimeria is monogenetic i.e. its life cycle is completed in one host only. 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 hosts in open.

1. Asexual Phase or Schizogony:

There are 2 generations of schizonts and merozoites which are morphologically.

i. First Generation Schizogony:

The beginning of complex life cycle of E. tenella may be taken to be initiated by the infection of epithelial cells of host caecum by sporozoites.

The infected fowl passes out oocysts or zygocysts with faecal matter. When these oocysts are swallowed by a new or healthy bird, its digestive juices dissolve the cyst-wall and release the sporozoites (or zoites) which enter the gut epithelial cells. Within the epithelial cells, the sporozoites grow in size any multiply by schizogony.

Sporozoite:

It is the earliest intracellular stage of parasite. It is elongated, slightly curved, microscopic unicellular organism with one end pointed and the other end blunt. The pellicle, forming external envelope, contains longitudinally arranged contractile microtubules which help in wriggling movements of the organism.

Cytoplasm includes a vesicular nucleus, a mitochondrion, Golgi bodies, endoplasmic reticulum, ribosomes, lysosomes and vacuoles containing reserve food, etc. Sporozoite penetrates into epithelial cell of host which is facilitated by the lytic secretion stored in the roptries of parasite.

Trophozoite:

The sporozoite soon increases in size and becomes pear-shaped. This stage of the parasite is called trophozoite. The characteristic feature of trophozoite is the presence of an eosinophil globule at its blunt end. This globule stains brightly with eosin and black with haematoxylin.

Trophozite absorbs nourishment through its general surface from the surrounding cytoplasm of the host cell. It grows considerably so that the host cell and its nucleus hypertrophy but are not destroyed.

Eventually, the trophozoite undergoes multiple fission by schizogony. Number of mitotic nuclear divisions is followed by the formation of cytoplasmic masses. This results in a multinucleate first generation schizont, which is somewhat oval in shape having vacuolated cytoplasm and many small nuclei.

Within the schizont, the peripherally arranged nuclei with cytoplasmic masses become pyriform bodies, the merozoites. As many as 900 merozoites may be produced by a single first generation schizont. Each merozoite is a very small and inconspicuous body, measuring about 2-4 µ in length and 1- 15 µ in width.

Its one end is pointed while the other end is rounded. The pointed end contains a terminal granule and the rounded end bears a number of cytoplasmic granules. The vesicular nucleus is present in the central position. The host cells containing schizonts are hypertrophied and are finally extruded into the lumen of the caecum. The schizonts burst and the first generation merozoites are released in the other epithelial cells.

ii. Second Generation Schizogony:

The liberated merozoites ready for new infections and schizogony may be repeated several times causing serious damage to epithelial cells. The first generation merozoite invades a fresh epithelial cell and comes to lie within its cytoplasm. It soon grows into a trophozoite. The trophozoite is similar to its counterpart of the first generation, except that it lacks an eosinophil globule. It feeds upon the cytoplasm of host and its nucleus undergoes repeated mitotic division forming a multinucleate schizont.

The second generation schizont differs very much from the first generation schizont. It is larger in size and the nuclei are present throughout its cytoplasm. Each nucleus has a distinct nucleolus or karyosome. Within the schizont the cytoplasmic divisions result in the aggregation of cytoplasmic bits around each nucleus. These nucleated cytoplasmic bits metamorphose into the second generation merozoites.

The second generation merozoites are also elongated and pyriform with rounded and a blunt ends. They are larger than the first generation merozoites, measuring about 16 µ in length and 2 µ in width. When the infected host cells become hypertrophied, the schizonts burst and the merozoites escape. They soon penetrate other epithelial cells lining the caecum.

2. Sexual Phase or Gametogony:

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 being to grow slowly and differentiates to form two kinds of cells called microgametocytes or male gametocytes and macrogametocytes or female gametocytes.

A male gametocyte is spherical having clear cytoplasm, while the female gametocyte is bean-shaped having its cytoplasm crowded with darkly standing refractile granules. Male gametocyte divides to form numerous narrow, biflagellate microgametes or male gametes. The female gametocyte extrudes chromatin from its nucleus and forms single macrogamete or female gamete.

The male and female gametes escape into the lumen of the gut where one male gamete fertilizes the female gametes to form a zygote by syngamy or anisogamy. In fertilization, 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 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. The mature oocyst is oval in shape and measures 20 – 60µ by 16.5 – 23µ.

3. Spore Formation Phase of 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. Here also some cytoplasm of each sporoblast divides of 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 nature oocyst contains four sporocysts each having two sporozoites. Thus there is an additional generation is sporogony by which each sporocyst gives rise to two sporozoites.

The oocyst containing four sporocysts and each sporocyst having two sporozoits 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 of Eimeria:

During the life cycle of Eimeria, the Schizogonic and sporogonic phases comprises the asexual generation as in these phases reproduction occurs by an asexual method of multiple fission. On the other hand gamogony represent the sexual generation as it involves the formation of male and female gametes. The asexual generation is always followed by the sexual generation. The phenomenon in which the sexual and asexual generations alternate with each other regularly is called the alternation of generations.

Term Paper # 4. Pathogenicity and Prevention of Eimeria:

Pathogenicity:

Eimeria cause a fatal disease called coccidiosis. The disease causes the destruction of the coccal epithelium resulting in bloody droppings.

The disease can be presented by providing proper hygiene conditions and with good management. Floor of lining place of chickens must be cleaned from time to time and the litter should be heaped to develop its temperature to 125°F. NH₃ can also be used to destroy the oocysts. The chickens suffering from coccidiosis are cured with sulpha drugs. Sulphamezoathene and Sulphaquinoxaline taken at the state of 0.5% with drinking water for a weak, prevents the disease completely.

Prevention:

The infection of young chickens may be prevented through proper hygienic conditions and with good range of management. The floors of the poultry houses, yards and ranges must be cleaned periodically by scrubbing them through the hot lye solution. The equipment used for rearing the birds should also be subjected to cleaning with the same solution.

As the moist litter is favourable for keeping the oocysts viable, it is recommended that the litter should be heaped to develop its temperature to 125°F. The use of ammonia in the dry litter destroys the oocysts.