Here is a term paper on ‘Leishmania’. Find paragraphs, long and short term papers on ‘Leishmania’ especially written for college and medical students.
Term Paper # 1. History and Habitat of Leishmania:
History:
Genus Leishmania was created by Ross in 1903. The species L. donovani was reported simultaneously Leishmania from London (1903). L. donovani infects man in India, China Russia, Mediterranean countries, and in parts of Africa and South America.
Habitat:
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Leishmania Donovani is one of the pathogenic protozoans which closely related to Trypanosoma. Various species of Leishmania infect horse, cows, dog, sheep and sometimes man even. The disease caused by this parasite is named after its name is Leishmaniasis. It is an intracellular parasite which causes the fever called Kala-azar. It is transmitted by sandfly from one heat to other heat.
In man, L. donovani lives as an intracellular parasite in leucocytes or cells of liver, spleen bone marrow, lymphatic glands, etc. it is the causative agent of the disease known as Kala-azar, causing enlargement of spleen and a reduction in the number of white corpuscles in blood.
Term Paper # 2. Shape and Structure of Leishmania:
Shape:
One parasite is seen in two shapes, i.e., either in oval or spindle shape, named as Leishmanial and Leptomonadial respectively. Its size varies from 2µ to 4µ in diameter and 15-20 µ in length.
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Structure:
The genus Leishmania occurs only in two forms i.e., leishmanial and leptomonade which alternate between a vertebrate (man) and an invertebrate (sandfly) host. The two forms are recognized as follows on the basis of the positions of their kinetoplast and blepharoplast, and by the position of flagellum.
The first form occurs intracellularly in blood cells or reticulo-endothelial cells of the vertebrate host or man. It is microscopic, rounded or oval, with a central or eccentric nucleus, blepharoplast and kinetoplast, but not free flagellum.
The second form found in the midgut of the invertebrate host or sandfly. It is elongated, slender and spindle-shaped with a large centrally placed nucleus, blepharoplast, kinetoplast and a long free flagellum. A fully formed promastigote stage measures 15-20µ in length and 1-2µ in width.
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Cell Membrane:
The whole body is covered externally by a very thin, delicate, elastic and firm covering or pellicle. It gives definite shape to the body and does not form an undulating membrane.
i. Flagellum:
Leishmania is uniflagellate, bearing a single flagellum. In the leptomonad form of parasite in sandy, the flagellum is long and free. It arises from a minute basal body or blepharoplast situated near the anterior end. Closely associated with the blepharoplast lies a disc-shaped parabasal body or kinetoplast. There is, however, no cytostome.
In the lesishmanial form of parasite in man, there is no free flagellum, as it is greatly reduced, fibril-like and lies embedded in cytoplasm. A transverse section of flagellum under electron microscope shows the typical 9 + 2 internal fibril arrangement.
ii. Cytoplasm:
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Underneath pellicle, the body cytoplasm is colourless, homogeneous and not differentiated into ectoplasm and endoplasm. Electron microscopic studies show that cytoplasm is marked by longitudinal striations or microtubules which may be contractile. Other structures present in cytoplasm are the blepharoplast kinetosome, rhizoplast, Golgi body, mitochondria, vacuole and nucleus.
iii. Nucleus:
A single large spherical nucleus lies eccentrically or in the middle of the body. It is vesicular and with a distinct central karyosome or nucleolus. It is covered by a double and membrane with pores and measures about 1 µ in diameter.
Term Paper # 3. Physiology of Leishmania:
As in Trypanosoma, a mouth or cytostome is also lacking in Leishmania, so that nourishment is obtained saprozoically through body surface from host cells. Gaseous exchange in respiration and elimination of excretory products also occur by diffusion through body surface. Sexual reproduction is unknown and asexual reproduction always takes place by longitudinal binary fission in the same manner as in case of Trypanosoma.
Term Paper # 4. Life Cycle of Leishmania:
Like Trypanosoma, Leishmania is also a digenetic parasite and requires two hosts for completion of its life cycle. Primary or principal host is a vertebrate or man, in which the parasite feeds and multiplies asexually. The secondary or intermediate host or vector is an invertebrate or blood-sucking insect or sandfly, belonging to the genus.
Phlebotomus:
Some mammals like dogs, and gerbils also serve as reservoir hosts in which the parasite do not undergo any change but simply waits for its introduction into the human host. In India, canine leishmaniasis does not exist so that man is the main and sole host. Under laboratory conditions small burrowing rodents or hamsters (Cricetidus griseus) are also susceptible to infection and utilized for testing the drugs for Leishmania infections.
Life Cycle in Man:
In India, L. donovani is transmitted to man by sandfly Phlebotomus argentipes. The insect vector, which has fed on some suitable fruit or plant juice after infected human blood meal, shows an enormous number of parasites in its buccal cavity and pharynx. Salivary glands of the vector are not involved as in case of a tsetse fly transmitting the trypanosomes.
When such a sandfly bites a man, it liberates the parasites in the skin wound caused by its proboscis. However, the actual mode of transmission is not clear in India. Perhaps the Indian vector (sandfly) does not bite but spreads infection by being crushed possibly by slapping.
The parasites introduced by sandfly into human body are in the promastigote or leptomonad form. Some of them entering the blood circulation directly become destroyed. While those entering the cells of reticulo-endothelial system (liver, spleen, bone marrow and lymph nodes) change into amastigote or leishmanial forms. These undergo slow multiplication by binary fission so that the host cells become greatly enlarged.
When the number of parasite reaches 50 to 200 or even more, the host cells ruptures. The liberated parasites are taken up by new host cells and the multiplication cycle is repeated so that the reticulo-endothelial system becomes progressively infected. Some of the free amastigotes become phagocytosed by neutrophils and monocytes (macrophages).
Life Cycle is Sandfly:
When a sandfly sucks blood an infected person, it obtains free amastigotes as well as the parasitized neutrophils and monocytes along with the blood-meal.
In the midgut of sandfly, the amastigote forms become elongated and acquire a free flagellum, thus changing into the promastigote forms. These multiply by longitudinal binary fission. In 6 to 9 days, the number of parasites becomes enormous and they spread into the pharynx and buccal cavity. The salivary glands are not infected. Transmission into a new host occurs when such a heavily infested sandfly bites the host.
Disease or Kala-Azar:
Incubation period is long, from 3 to 6 months, and symptoms may appear even after 2 years. Early symptoms of Kala-azar include swelling, high fever and enlargement of spleen and liver. It is followed by general weakness, emaciation, anemia due to reduction in number of blood cells, and a peculiar darkening of skin.
The word “Kala-azar” has been derived from two Indian words, kala and azar, meaning “Black sickness”. In advanced stage, skin becomes dry, rough and dark or pigmented. Hair becomes brittle and falls out. If not properly treated, the patient dies within 2 years. Death is generally due to secondary infections by bacteria or viruses. The defense mechanism of body becomes so weak that the patient is unable to resist them.
Treatment of Kala-Azar and Its Prevention :
Kala-azar is treated with two drugs, i.e. pentavalent antimony compounds used in sodium-antimony tartrate and gluconate, urea, aminostiburea etc. Sometime pentamidine is ethionate and is also used for treating the patient suffering from Kala-azar.
However, the prevention of the disease can be done as follows:
(i) Eradication of the Insect Vector:
In endemic areas low trees and bushes, etc. should be cleared out and sandflies should be removed. Periodic fumigation and spray of insecticides of sleeping quarters should be done.
(ii) Attack on the Parasite:
In areas where dogs act as reservoir hosts, all street dogs should be killed.
(iii) Personal Defense:
For avoiding bite of sandflies, use mosquito-nets or screens and avoid sleeping on ground floors.