Parasite

Parasite: A plant or animal organism that lives in or on and takes its nourishment from another. Parasite diseases include infections due to protozoa, helminths, or arthropods. For examples: Malaria is caused by plasmodium, a protozoa (a single-cell organism that can only divide within a host organism). Schistosomiasis, another set of very important parasitic diseases, is caused by a helminth (a worm). The arthropods include insects and arachnids (spiders, etc.), a number of which can act as vectors (carriers) of parasitic diseases.