Ascaris Roundworms
These roundworms, while microscopic, cause enough damage in the small intestine of a human that wreaks havoc on the entire body. Humans get infected by accidentally ingesting their eggs, whether from raw produce or water, in developing countries in Asia and South America. Death from this roundworm happens more often where treatment is not found, in places with ineffective sewage disposal systems.

Symptoms from heavy infections include loss of appetite, poor absorption of nutrients from food, and unexplained weight loss. Children who are infected with this roundworm typically experience stunted growth, since their body is unable to absorb important nutrients. If a large number of eggs are swallowed and then move to another part of the body, it could cause bowel obstruction, which causes a variety of problems down the line (Far and Wide).