Parasites are living Marco or microorganisms which uses other living things such as our body, food or a place to live. It is an infectious disease and it occurs due to contaminated water or food, or due to a bug bite, or sexual contact. Only some parasitic diseases can be easily treated and some cannot be. The size of the Parasites vary from tiny, one-celled organisms called protozoa to worms which can be seen with the naked eye. Giardia infections are led by the contaminated water supply. Others, like malaria, are common in other parts of the world.