Ecology of Parasitism in Human Beings’
نویسندگان
چکیده
Parasitic infections are influenced by three closely interrelated factors: the parasite, the host, and the environment. Endemicity depends upon the simultaneous occurrence of certain biological and ecological conditions that affect the parasite and the host. Parasites must first of all be present in specific numbers; they must possess the proper pathogenicity and adaptability to the host and the environment; they must produce enough cysts, oocysts, eggs, and larvae to ensure their dissemination over the environment; they must survive the trials of the environment; and some types must be able to pass from one host or vector to another. There must likewise be a sufficient number of susceptible hosts to contract and maintain the infection. The resistance or susceptibility of a host species to parasitic infection depends on natural or acquired immunity factors which tend to create favorable or unfavorable biochemical and biophysical conditions. Other contributing factors are the age, nutritional status, and genetic history of the host. In humans other circumstances again, peculiar to man’s social condition, are important (1).
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