Ecología del parasitismo en el hombre

Abstract

Three closely related factors play a role in parasitic infections: the parasite, the host and the environment. To establish endemicity, certain biological and ecological conditions that act on the parasite and its host must occur in conjunction

The parasites must be present in specific numbers; possess suitable pathogenicity and adaptability to the host and to the environment; produce a sufficient number of cysts, oocysts, eggs or larvae to guarantee their dissemination through the environment; and succeed in passing from one host to another

There must also exist a sufficient number of susceptible hosts capable of contracting and maintaining the infection. A host species' resistance or susceptibility to the parasitic infection depends upon natural or acquired immunity factors which determine favorable or unfavorable biochemical and biophysical conditions. The host's age, state of nutrition and genetic line also play a part

Most parasites have little pathogenicity and disease appears when certain favorable condition - biological, ecological, and, in particular, human - occur in conjunction. Highly virulent parasites succeed in destroying their hosts and, consequently, endanger themselves in the process. Natural selection tends to eliminate the more pathogenic species and, on the other hand, favors the survival of the less virulent types which can coexist with their hosts without causing ... (AU)