View source for Blastocystis species

==Background==
*Anaerobic [[protozoa]]n [[parasites]]
*Found in the human gastrointestinal tract <ref> Tan KS. New insights on classification, identification, and clinical relevance of Blastocystis spp. Clin Microbiol Rev. 2008;21(4):639-665. doi:10.1128/CMR.00022-08 </ref>
*Most common eukaryotic parasites found in human stool
*Controversial if they are a commensal organism or a pathogen

===Epidemiology===
*Have been found worldwide
*Reside in the cecum and colon of both children in adults
*Have also been found in various animals (including pigs, monkeys, rodents, and poultry) 
*Prevalence is geographically variable, but generally higher in developing countries

===Transmission=== 
*Mode of transmission is not fully understood, but though to be fecal-oral <ref> Blastocystis hominis: commensal or pathogen? Lancet. 1991 Mar 2;337(8740):521-2. PMID: 1671894. </ref> 

===Microbiology===
*Vary in size between 5 and 40 micrometers
*Lack a cell wall
*Have mitochondria, golgi apparatus, smooth and rough endoplasmic reticula
*Typically reproduce by binary fission
*Grow in anaerobic culture conditions

==Clinical Features==
*Symptoms that have been associated with individuals with Blastocystis species in their stool include: 
**Watery [[diarrhea]] (may be acute or chronic)
**[[Nausea]]
**Anorexia
**Fatigue
**[[abdominal pain|Abdominal cramping]]
**Bloating
**Flatulence 
**[[Urticaria]] 
*Generally patients are afebrile

==Differential Diagnosis==
{{Diarrhea DDX}}

==Evaluation==
*Stool examination via light microscopy of stained smears or wet mounts
*Stool culture <ref> Suresh K, Smith H. Comparison of methods for detecting Blastocystis hominis. Eur J Clin Microbiol Infect Dis. 2004;23(6):509-511. doi:10.1007/s10096-004-1123-7 </ref>
*ELISA targeted at serum antibodies to Blastocystis species <ref> Zierdt CH, Zierdt WS, Nagy B. Enzyme-linked immunosorbent assay for detection of serum antibody to Blastocystis hominis in symptomatic infections. J Parasitol. 1995;81(1):127-129. </ref>
*PCR <ref> Jones MS 2nd, Ganac RD, Hiser G, Hudson NR, Le A, Whipps CM. Detection of Blastocystis from stool samples using real-time PCR. Parasitol Res. 2008;103(3):551-557. doi:10.1007/s00436-008-1006-4 </ref>
*Fecal leukocytes are usually absent


==Management==
===Asymptomatic===
*Do not require therapy

===Symptomatic===
*Alternative diagnoses should be considered and excluded (e.g. alternative pathogen, noninfectious cause of symptoms)
*Initiation of treatment in symptomatic patients is controversial 
*Blastocystis species infection is often self-limiting and many mild cases will resolve quickly
*Treatment options:
**[[Metronidazole]] (750 mg TID for 5-10 days) <ref> Nigro L, Larocca L, Massarelli L, et al. A placebo-controlled treatment trial of Blastocystis hominis infection with metronidazole. J Travel Med. 2003;10(2):128-130. doi:10.2310/7060.2003.31714 </ref>
**[[Tinidazole]] (2 mg once)
**Alternatives include: paromomycin, nitazoxanide, and trimethoprim-sulfamethoxazole 

==Disposition==
*Most patients can be managed as an outpatient 
*Admission or observation should be considered for patients who are severely dehydrated or have significant electrolyte derangements

==See Also==

==External Links==

==References==
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