Q.3. Give an account of various disease causing protozoa in human beings.
Related Questions-
Q. Write on protozoa diseases. (1997)
Q. Write the name of five parasitic protozoans and the disease.
Q. Write the name of parasities causing dysentry, malaria, diarrhea and sleeping sickness in man. (2007)
Ans. Certain pathogenic parasities cause some of the worst human diseases. some of these are described below.
1. Amoebiasis: -
Amoebiasis, or amoebic dysentery, is caused by Entamoeba histolytica (Sarcodina). Its trophozites, that penetrate the wall of intestine (colon), secrete histolytic enzymes and feed upon its cells causing the formation of ulcers. These ulcers rupture and discharge blood and mucus into the intestine that pass with stools. The trophozoites, under certain circumstances, reach liver, lung and brain where they cause abscess formation.
No intermediate host is involved in the life cycle of parasite. Transmission of parasite from man to man takes place through tetranucleate cysts. Prior to cyst-formation the trophozoite changes into a smaller minuta form, which then encysts to form a tetranucleate cyst. These cysts are avoided with faecal matter and new hosts. Houseflies help in its rapid spread.
2. Diarrhoea: -
Giardia intestivaties causes diarrhoea which characterized by loose bowels. It is a flagellate parasite which harbours the small intestine. Its cell body is pear shaped with dorsal side convex and ventral side flattened. It bears two nuclei and four pairs of flagella arranged symmetrically.
The parasite divides by binary fission to multiply rapidly and feeds upon amino acids and vitamins contained in the food within the intestine. This causes intestinal disorders.
Transmission of the parasite takes place through cysts which are avoided with the new hosts in food or water. The infection of giardia is more in children than in adults.
3. Trypanosomiasis: -
It is causes by trypanosoma which are flagellate parasites of the blood and gut. Sleeping sickness is a dangerous disease of man in tropical africa. Its causative agent is T.gambiense and is transmitted by a tse tse fly, glossinia palpalis. Infestation of the lymph system leads to glandular swelling which is a prominent feature of sleeping sickness. Later the parasites penetrate into the cerebrospinal fluid causing damage to the brain and bring about the lethargy characteristic of sleeping sickness.
T.cruzi is the causative agent of american trypanosomiasis or chaga’s disease. It is transmitted by bugs of the genus Triatoma. Transmission to man is not due to bug bite but through its faeces.
4. Leishmaniasis: -
It is caused by the species of leishmania, the parasitic flagellates that inhabit phagocytotic cells leismaniasis. It is also a parasitic flagellate that inhabit phagocytic cells in body organs in vertebrates and gut in insect hosts. Leishmania donovani is the causative agent of kala azar or visceral leishmaniasis. A major characteristic of this disease is a considerable enlargement of the spleen due to blockage of reticuloendothelial system by parasites.
L.tropica is the causative agent of skin leishmaniasis (oriental sore). The infection is restricted to the endothelium of skin capillaries and leads to lump like boils.
L.brasiliensis causes a disease called espundis, producing multiple sores over large areas of the body. Development of ulceration in nasal cavities, mouth and pharynx is quite frequent.
Leishmania species are transmitted from man to man by bites of sandflies belonging to the genus phlebotomus.
5. Trichomoniasis: -
This disease is caused by the species of Trichomonas, the flagellate protozoans. Its body is rounded with one nucleus, an axostyle, a parabasal body, 4-6 flagella and one backwardly directed flagellum. The most common pathogenic species is Trichomonas vaginalis that inhabits vagina of woman and causes vaginitis. The disease is characterized by inflammation, burning sensation, and frothly vaginal discharge. Transmission is always through sexual intermediaries. Arsenic and iodine drugs and antibiotics in like Aurreomycin and terramycin, have proved helpful in combating the disease.
6. Malaria: -
It is caused by plasmodium which is a sporozoan parasite. It is transmitted through the bite of female anophles mosquito. In man, the parasite attacks the liver cells and the red blood cells. A toxic substance the haemozoin released by the parasite causes malaria.
Malaria is characterized by the periodic attacks of fever. The fever is repeated in the tertain malaria caused by P.vivax every third day, in ovale malaria caused by P.ovale every third day, in quartan malaria caused by p.malariae every fourth day and in malignant tertian malaria caused by P.falciparum every third day.
Various drug used in the treatment of malaria include Quinine, Atebrin, Chloroquine, Camoquine, Pamaquine, Paludrine, Daraprim, etc.
7. Toxoplasmosis: -
Toxoplasmosis is caused by Toxoplasm gondii, a sporozoan parasite. The parasite occupies the cells of the reticulo-endothelial and central nervous systems. The parasites multiply by endodyogeny but under certain conditions large cysts are also produced. An infacted woman concieves, abortion takes place. If infaction of T. gondii occurs during pregnancy, in third trimester then nervous system of the developing foetus is affected and the infant dies after brith. Daraprim, combined with sulphadiazine has been found to be an effective remedy.
Q.4. Write an esay on protozoa and its parasitism. (2009)
Ans. Parasitism in protozoa: -
1. Parasite and parasitism: -
Parasites may be defined as “the species which exist at the expense of certain other species, called hosts, and are biologically and economically closely connected with them throughout their life-span”, Parasitism is an association between the parasities and their hosts. It may be defined as “an association between two organisms of such kinds that one (parasite) lives and feeds, temporarly or permanently, either in or on the body of the other (host)”.
2. Types of parasities: -
There are four types of parasites in protozoa :
1. Ectoparasites: -
Those protozoa which inhabit the external surface of their hosts. Hydramoeba hydroxena, feeding on the ectodermal cells of Hydra and Ichthyophthirius multifilis, burying in the epidermis of freshwater fishes, are examples of ectoparasitic Protozoa.
2. Endoparasites: -
Those parasites which live inside the body of their hosts. These are divided into four categories :
(a) Parasites of digestive tract: -
Those endoparasites which dwell inside the lumen of alimentary canal of hosts. Giardia lamblia , a parasitic flagellate, entamoeba histolytica, a parasitic amoeba, Isospora hominis, a parasitic coccidian, Balantidium coli, a parasitic ciliate, are all intestinal endoparasites of man.
(b) Parasites of mouth: -
Those endoparasites which reside in mouth cavity of hosts. In man, entamoeba gingivalis and Trichomonas tenax are found in pockets between the gums and teeth.
(c) Parasites of genital tract: -
Those endoparasites which inhabit the genital tract of hosts. In human female, Trichomonas vaginalis lives in vagina.
(d) Parasites of body tissues: -
Those parasites which live within tissues of hosts and may enter through skin or from disgestive tract. Species of Trypanosoma, Leishmania, Plasmodium and Babesia are common blood parasites of vertebrates.
3. Hyperparasites: -
These are protozoa parasitizing other species of parasitic Protozoa. For instance, the opalinid (Zelleriella) which lives in the frog’s intestine, is parasitized by a certain amoeba. Nosema notabilis parasitizes Sphaerospora Polymorpha which is a parasite of urinary bladder of toad fish.
4. Pathogenic parasites: -
Most of the parasitic protozoans do not cause disease conditions in their hosts except producing minor symptoms. On the other hand, certain parasites act as disease-causing organisms in man and other animals. Such parasites are referred to as pathogenic parasites. Important pathogenic parasites of man are Leishmania donovani, Trypanosoma gambiense, Plasmodium vivax, Entamoeba histolytica, etc.
(iii) Host specificity: -
The two group are exhibited regarding the most specificity. Firstly some parasites can successfully parasitize a wide variety of hosts. Trypanosoma, Entamoeba and Eimeria belong to this group. Secondly, some parasites have become restricted to only a few specific host. Coccidia of mammals (e.g. Plasmodium) are such parasites.
(iv) Transmission: -
There are different way for transiting the parasites. Entamoeba gingivalis is transferred directly from one man to another through machanical contact, like kissing (direct transfer). Some such as Entamoeba histolytica and Eimeria tenella, are transferred by cysts in water or food (contaminative transfer). Species of Trypanosoma, Plasmodium, etc. are transmitted by certain invertebrate vectors (inoculative transfer). Transmission by invasion of ovary or egg takes place for species of Babesia. Placental transference has been reported for Plasmodium in man (congenital transfer).
(v) Life cycle: -
many parasites, such as Eimeria and Monocystis, have only a single host during their life cycle, only a part spent outside the host. These are called monogenetic parasites. Other protozoan parasites (e.g. Plasmodium, Trypanosoma) have two or more hosts, two hosts are usually desigmated as the primary host, in which the parasite’s ancestors evolved and the secondary host or vector, which acts as a transmitting agent for the parasite to the other host. These are called digenetic parasites. If the parasites undergoes part of its life cycle in vector, its transmission is called cyclical, if not it is referred to as mechanical transmission. Some other animals may be infacted by the parasites and serve as a source for infacting other animals. These animals constitue the reservoir hosts.
(vi) Effects of parasites on their hosts: -
Some parasites protozoa prove to be injurious for theirhosts, while others produce almost no effect. Entamoeba histolytica destroys host’s large intestine causing large unlcerations. Eimeria stiedae is known to cause hyperplasia of the hepatic cells of rabbits. The coccidian parasites of earthworm, Polymnia nebulosa, brings about hypertrophy of the sperm mother cells. The malarial parasites of birds, Plasmodium gallinaceum, clogs the fine blood capillaries etc.