PHYLUM: PROTOZOA Parasitisnm
PARASITISM IN PROTOZOA Parasitism is a Greek word which means eating beside one another (para-beside, sitos-food). Parasites are the species which live at the expense of certain other species. The other animals on which the parasites live are called as hosts. . The parasites are biologically and economically closely connected with the hosts throughout their life time.
.Hence parasitism can be defined as an association between the parasites and their hosts. It is an association between two organisms whereby the parasite temporarily or permanently lives and feeds in or on the body of the host. . Almost all the protozoan groups have parasitic species and the group Sporozoa is exclusively parasitic.
Types of parasites: Ectoparasites:These are the parasites which inhabit the external surface of their hosts. . Eg: Hydramoeba hydrozena feeding on the ectodermal cells of hydra, lcthyopthirius multifilis burying in the epidermis of freshwater fishes Endoparasites:These are the parasites which inhabit the internal surfaces of their hosts.
They may be further subdivided into the following types, The parasites which dwell in the lumen of the alimentary canal of the host. Eg:Entamoeba histolytica, Giardia lamblia, Isospora hominis, Balantidium coli . The parasites which reside in the mouth cavity of hosts. Eg:Trichomonas tenax, Entamoeba gingivalis The parasites which inhabit the genital tract of the hosts. Eg:Trichomonas vaginalis The parasites which live within the tissues of hosts, These may enter the host tissues through the skin or even from the digestive tract. Eg:Trypanosoma, Plasmodium, Leishmania, Babesia
Hyperparasites: These are the protozoans which parasitize other parasitic protozoans. In other words these are parasites on parasites.Eg:Zelleriella, Nosema notabilis, Sphaerospora polymorpha Pathogenic parasites:Generally the parasitic these parasites are pathogenic and can cause grave diseases in humans and other animals. These parasites which are causing disease are called as pathogenic parasites. Eg:Leishmania donovani, Plasmodium vivax, Trypanosoma gambiense
Host specificity: The protozoan parasites are generally host specific. Firstly, some of the parasites like Trypanosome, Entamoeba and Eimeria successfully parasitize wide range of hosts. Secondly, some parasites like Plasmodium restrict themselves only to few specific hosts.
Effects of protozoan parasites on their hosts: The parasites can bring about several changes within their hosts. Some parasites can also prove to be injurious to the host, while others may produce no effect on the host. The following are the few examples, Entamoeba histolytica destroys the large intestine of the host and this in turn causes ulcerations. Eimeria stiedae causes hyperplasia of the liver cells of rabbits. Polymnia nebulosa which is a parasite of earth worm brings about hypertrophy of the sperm mother cells. Plasmodium gallinaceum which is malarial parasite of bird clogs fine blood capillaries.
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