This is a single celled parasite that infects the gastrointestinal tracts of humans, animals, birds rodents, reptiles, amphibians, fish and cockroaches.
The most frequent symptoms are abdominal pain, constipation and diarrhea. It was originally thought to be protozoan but is now classified as a stramenopiles. Other stramenopiles include brown algae, mildew and diatoms. They all have 4 various life cycle stages including cyst forms. The blastocystis cyst form can infect humans with 9 species able to do this.
The blastocystis cyst form is the way the infection is transmitted. It is also very resistant to chemicals in this form and is able to survive in harsh conditions because of its multi-layered cyst wall. Blastocystis can remain in the intestines for weeks, months or years with many people having no symptoms at all. This parasite is very common in developing countries although it is also prevalent in many parts of Australia.
The cyst form varies enormously in size between 1 and 200 microns with an average size of 6-40 microns. Standard high quality 1 micron filtration should remove this parasite from the water although sub-micron absolute filtration would be recommended as a better preventative measure.