Some common parasites that do not usually make someone sick, but can cause people to worry, are listed below. Many of these non-pathogenic parasites do not cause symptoms. People with these parasites should discuss need for treatment with their health care provider.
Diagnosis of these parasitic infections is done by stool culture and can be difficult. A person may be shedding parasites or eggs one day, but there may be no shedding the next day.
A person can carry more than one parasite at a time, but they may not all be present in one stool sample. A person should provide one stool sample three days in a row to ensure a representative sample of what is in their bowel.
Most of these parasites are considered normal in the environment and are found in surface water and soil.
Dientamoeba fragilis
This parasite is transmitted along with pinworm eggs. Children are most commonly infected and may experience abdominal pain and diarrhea.
It is estimated that symptoms appear in only 15% to 27% of those infected.
Blastocyctis homonis
Contaminated water is the most common vehicle for transmission. The amoeba can survive in a wet environment for several weeks. In its dormant stage it will survive even cold temperatures for months.
Infection with Blastocyctis homonis typically occurs in conjunction with other organisms, it is unclear if this parasite causes disease on its own or if the other organisms are the cause of the symptoms. It may cause diarrhea and cramping, however, most people do not develop symptoms.
Endolimax nana
This is one of the smallest parasites and is usually spread through swallowing contaminated water or food. As many as 60% to 70% of people infected experience diarrhea, and sometimes a low-grade fever.
Other commonly-isolated amoebas are usually picked up by drinking or eating contaminated water or food.
There are very few symptoms involved, but the amoebas may cause nausea and bloating.