DISON

Hi, I'm Ann Jay, relationship coach and therapist. In the context of communicable disease, the host-parasite relationship must be considered not only with respect to the individual host-parasite interaction but also in terms of the interrelationship between the host and parasite populations, as well as those of any other host species involved. The condition of obligate parasitism is associated with a degree of specificity of the parasite with regard to the host; i.e., the parasite generally is more closely adapted to one species of host than to all others. A number of host species may be susceptible to infection with a given parasite, and the pattern of host susceptibility need not correspond with taxonomic relationships, including hosts varying as widely as vertebrates and invertebrates. Disease produced in related host species may be either milder or more severe than in the definitive host. A greater degree of dependence on the host is shown by rickettsiae and viruses. Viruses are obligatory intracellular parasites, capable of multiplying only within the cells of the host, and they have no independent metabolic activity of their own.