It is a parasite, that lives in animal and human gastrointestinal tract, and causes different symptoms among which are abdominal pain, constipation, diarrhea, weight loss, fatigue, and abdominal bloating.
A medical condition caused by infection of this parasite is known as a blastocystosis.
Using untreated water and vegetables contaminated with that water are usual sources for this infection.
Metronidazole and other antiprotozoal drugs are used to tread blastocytosis.

The correct therapy according to your child age can be given only by her pediatrist or infectologist.

Thank you for your response. It is very informative.