Every organism has to cope with an assortment of predators and parasites.
Many biologists feel that one of the most potent forces of evolutionary adaptation is that created by the interactions between a host and its parasites. As the host evolves measures that give it greater protection from a parasite, the parasite evolves countermeasures. This page examines some of the mechanisms by which parasites evade host defense measures. The emphasis will be on human parasites. Gaining Superficial Entry Most parasites enter their human host through food and water air the bites of arthropod vectors like mosquitos, fleas, and ticks.