What are the key features of parasites?

Parasitic organisms (or parasites) refer to living things which sustain themselves, obtaining nutrients and other resources, at the expense of another organism that they live on or within, known as the host, forming what is known as a host-parasite relationship. Such a relationship may be necessary for the parasite to survive (in which they are obligate parasites) or not (facultative parasites). As mentioned parasites may either live on the surface of the host (ectoparasites) or within the host’s body (endoparasite). There are a large variety of examples of parasites, including but not limited to, micro-organisms, insects and worms. Parasites can be pathogenic and cause some of the world’s deadliest infectious diseases. For example malaria is caused by the protozoan parasite Plasmodium falciparum which is transmitted by mosquito vectors of the Anopheles genus to human hosts. Parasites are able to exploit their host in a variety of ways, one of which is by directly taking nutrients from their hosts. For example the tapeworm Taenia solium is able to absorb nutrients in the digestive tract of its human or pig host after strongly attaching to the walls of the small intestine. To survive parasites are often highly specialised to the parasitic lifestyle, like Taenia, to help create and maintain the parasite-host relationship.