Parasitism describes the phenomenon within the animal and plant world that an organism or virus (parasite) misuses a usually considerably larger organism of a different species as a host. The host serves the parasite for food supply (mostly in the form of blood or other body secretions) and in some cases also as a long-term habitat. The host's health is damaged by the parasite, but usually remains alive. The consequences of parasitic infestation range from sting or bite injuries from massive physical complaints to serious infectious diseases and even death in extreme cases. The best known and most widespread human parasites are human lice, mosquitoes and various types of ticks and worms.
