Parasite

>Protozoa -- Malaria is caused by plasmodium, a protozoa, a single-cell organism that can only divide within its host organism.

>Helminths -- Schistosomiasis, another set of very important parasitic diseases, is caused by a helminth (a worm).

>Arthropods -- The arthropods include insects and arachnids (spiders, etc.), a number of which can act as vectors (carriers) of parasitic diseases.

</LI></UL> The term 'parasite' came from the Greek 'parasitos' (para-, along side of + sitos, food) meaning 'eating at the side of, as at the same table.' The sense of the term later changed to that of a poor friend or relative who lived at the expense of another.

Not until the 18th century did 'parasite' come into English as a biologic term.

The study of parasites is parasitology.