Parasitism is one of the many forms of symbiosis. In parasitism, one organism (called parasite) benefits at the expense of another organism usually of different species (called host). The parasite benefits at the expense of the host organism. Depending on the type of parasite involved, the parasitism may be an ectoparasitism or an endoparasitism. Ectoparasitism is a form of parasitism where the parasite lives outside the body of the host. The parasite is referred to in particular as an ectoparasite. In ectoparasitism, the host-parasite relationship is non-mutual. Many of the endoparasitic relationships do not lead to much harm to the host compared with that in endoparasitism. Nevertheless, there are ectoparasites that serve as carriers of disease. For instance, the mosquito, Aedes aegypti, may carry dengue virus, which can cause dengue. The mosquito is an example of an ectoparasite since it benefits from its host, e.g. human, by feeding on the blood of the latter. Other examples of ectoparasitism are ticks, lice, and leech that feed externally from the skin of their host.