Pathogen - A biological agent that causes disease.⏎
Protozoa - A taxonomic group of single-celled microorganisms that live in almost every kind of habitat and include some pathogenic parasites of humans and other animals. ⏎
Nanometer - A unit of length equal to one one-billionth (1 x 10-9) of a meter.⏎
Reservoir - An organism in which a parasite that is pathogenic for some other organism lives and reproduces without harming its host.⏎