The term parasite refers to organisms that infest another organism where it lives and feeds. Some of these parasites are microscopic and not visible to the naked eye whereas other parasites are relatively large. Human intestinal parasites are either one-cell organisms or intestinal worms that live in the small or large intestine and consume nutrients from the intestinal lumen or the blood flowing in the intestinal wall.
Both protozoan and helminths (worms) are primarily contracted through ingesting contaminated food or water. The adult parasite or its eggs are shed in the stool of humans or animals. This can then contaminate water sources suahc as rivers and lakes as is the case with open sewage or poor water treatment practices. Drinking, bathing or irrigating crops with this contaminated water then allows the parasites to enter the body.
In some instances, parasites can be spread from person to person mainly when one person comes into contact with the fecal particles of a person who already has an infestation. This puts certain people at a greater risk. For example a caregiver changing diapers or cleaning soiled lined of a person who already has an infestation or infection may therefore be at risk of contracting the infection.