Blastocystis hominis

Blastocystis hominis is a parasite that is found throughout the world. Little is known about how it is transmitted to
humans. Some people who are infected have symptoms and some do not. Treatment is available but is not always
effective.

Watery or loose stools, diarrhea, abdominal pain, anal itching, weight loss, and excess gas have all been reported in
persons with Blastocystis infection. Many people have no symptoms at all.

Blastocystis can remain in the intestines for weeks, months, or years.
http://www.cdc.gov/ncidod/dpd/parasites/blastocystishominis/factsht_blastocystis_hominis.htm#what

The taxonomic classification of Blastocystis hominis is mired in controversy.  It has been previously considered as
yeasts, fungi, or ameboid, flagellated, or sporozoan protozoa.  Recently, however, based on molecular studies,
especially dealing with the sequence information on the complete SSUrRNA gene, B. hominis has been placed within
an informal group, the stramenoiles (Silberman et al. 1996).  Stramenopiles are defined, based on molecular
phylogenies, as a heterogeneous evolutionary assemblage of unicellular and multicellular protists including brown
algae, diatoms, chrysophytes, water molds, slime nets, etc. (Patterson, 1994).  Cavalier-Smith (1998) considers
stramenopiles to be identical to his infrakingdom Heterokonta under the kingdom Chromista.  Therefore, according to
Cavalier-Smith, B. hominis is a heterokontid chromista.
http://www.dpd.cdc.gov/dpdx/HTML/Blastocystis.htm

Symptoms
The signs and symptoms that might be associated with blastocystosis include:

Diarrhea,  Nausea,  Abdominal cramps,  Bloating,  Excessive gas (flatulence),  Anal itching,  Fatigue
http://www.mayoclinic.com/health/blastocystis-hominis/DS00791/DSECTION=symptoms