High Quality Content by WIKIPEDIA articles! Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host (e.g. Taenia solium). These are now called macroparasites (typically protozoa and helminths). The word parasite now also refers to microparasites, which are typically smaller, such as viruses and bacteria, and can be directly transmitted between hosts of the same species.