Method and Organism Discussions

Discussion #2C: Diagnosis, Treatment, and Prevention of Blastocystis spp.

General Information

Blastocystis comprises a multitude of subtypes, many of which have been identified only recently; molecular epidemiological studies have revealed a significant difference in the distribution of subtypes across host species and geographical regions. Worldwide, Blastocystis is very commonly found in the stools of individuals with and without intestinal symptoms; it is the most common parasite found in stool specimens, while Giardia and Dientamoeba follow and may vary between the second and third most common parasite in stools. Following the introduction of molecular methods, the prevalence and intra-generic diversity of Blastocystis are becoming more well defined. Confirmation of the existence of these subtypes and determination of their pathogenic status may also explain why some patients are asymptomatic and some have clinical symptoms. Currently it is estimated that more than 1 billion humans across the world are colonized with Blastocystis.

Several studies have described the genetic diversity present in Blastocystis, which has led to its classification as having multiple subtypes (STs) in its different lineages, based on polymorphic regions of its small subunit of the ribosomal RNA gene. Some of these STs are found in different hosts, but others are exclusively in humans. Currently, 17 subtypes are known, of which ST1 to ST9 and ST12 have been identified in humans. In humans from Europe, STs 1, 2, 3 and 4 reportedly occur most commonly, whereas ST1, 2 and 3 commonly occur in South America. More than one ST can reportedly colonize humans, and infections with mixed STs have been reported.

Blastocystis may cause clinical manifestations such as diarrhea, abdominal pain, irritable bowel syndrome, constipation and flatulence, along with extraintestinal manifestations such as chronic urticaria.

Hosts

Blastocystis has been detected in stools from humans and a wide range of non-human animals (e.g. canids, swine, primates, rodents, birds, etc.).

Geographic Distribution

Blastocystis sp. is found worldwide. Efforts to characterize the geographic and host distribution of Blastocystis subtypes are ongoing.

Diagnosis

The standard O&P exam is recommended for recovery and identification of Blastocystis spp. in stool specimens. Microscopic examination of a direct saline wet mount may reveal small to large ‘‘central body’’ forms. An asymptomatic individual may have few organisms present, all of which are the same central-body forms. Although other forms are present in the gut (primarily in patients with diarrhea), the morphology is difficult to identify; identification relies almost exclusively on the presence of the central body form. While the concentration technique is helpful in demonstrating these organisms, the most important technique for the recovery and identification of protozoan organisms is the permanent stained smear (normally stained with trichrome or iron hematoxylin). A minimum of three specimens collected over not more than 10 days is often recommended.

Genetic Signatures' EasyScreen™ Gastrointestinal Parasite Detection Kit and GS1 automated workflow has been FDA 510(k) cleared for sale in the United States. This system can detect and identify 8 important GI parasites in a single test, including the following organisms:

Giardia lamblia / intestinalis (Varies with D. fragilis between #2 and #3 most common parasites found in stool specimens)
Cryptosporidium spp
Entamoeba histolytica
Cyclospora cayetanensis
Dientamoeba fragilis
Blastocystis spp. (Most common parasite found in stool specimens)
Enterocytozoon bieneusi (Microsporidia)
Encephalitozoon intestinalis (Microsporidia)

Treatment

Drugs that have been used for the treatment of Blastocystis infection include the following. There are contraindications in pregnancy and pediatric patients:

https://www.cdc.gov/blastocystis/hcp/clinical-care/index.html

Metronidazole
Trimethoprim-sulfamethoxazole
Nitazoxanide

Prevention

From present information, it appears that Blastocystis is transmitted via the fecal-oral route through contaminated food or water. Although other possible modes of transmission are not defined, the incidence and apparent worldwide distribution indicate this traditional route of infection. Recent studies suggest the existence of numerous zoonotic isolates, with frequent animal-to-human and human-to-animal transmissions, and of a large potential reservoir in animals for infections in humans. To prevent a Blastocystis infection, you can practice good hygiene and avoid contaminated food and water:

Wash your hands:Wash your hands with soap and water for at least 10 seconds after using the toilet, before handling food, and after changing diapers.
Wash fruits and vegetables:Wash and peel all fruits and vegetables before eating them.
Avoid contaminated food and water:Avoid food or water that may be contaminated by sewage.
Boil water:In countries where the water supply may be unsafe, boil water before drinking it or using it to cook.
Use bottled water:If you can't boil water, use bottled water.
Use a filter:Use a filter with an absolute pore size of 1 micron or smaller, or one that has been NSF rated for “cyst removal”.
Treat water chemically:If you can't boil or filter water, you can treat it chemically by chlorination or iodination.
Keep cooking surfaces clean:Keep cooking surfaces clean
Teach children to wash their hands:Teach children the importance of handwashing.