Organisms can use other species not only as a habitat, but also as a constant source of nutrition. This form of cohabitation is called parasitism. Several tens of thousands of parasitic forms are known, of which about 500 are human parasites. Parasites cause great damage to agriculture. The science of parasitology is engaged in the study of their vital activity, ways of distribution and the development of measures to combat parasitic diseases.
Forms of parasitism can be very diverse. True parasitism is an evolutionarily logical form of the relationship between two organisms, when another form of existence for the parasite is impossible, while true parasitism can manifest itself as obligate, that is, mandatory and constant for this type of organism, and as optional, when the life cycle of the parasite can include a free lifestyle, and when it enters another organism, it parasitizes in this host organism. An example of true obligate parasitism is the presence of malarial plasmodia in the blood, flukes in the host liver, roundworms in the intestines, scabies itching in the skin, etc. Optional parasitism can include the introduction of intestinal cinnamon larvae into the human body through the skin and their migration into the intestines, although they can develop under favorable conditions in the soil. In addition, there is a false parasitism, which is a random phenomenon for this species, while the false parasite retains viability in the host organism for some time and harms it, but an independent lifestyle is common for it. An example of false parasitism is getting leeches in a person’s nasopharynx while swimming. Such false parasitism of leeches can lead to the death of the host as a result of airway obstruction or bleeding.
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