Blastocystis species
Background
- Anaerobic protozoan parasites
- Found in the human gastrointestinal tract [1]
- 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 [2]
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 cramping
- Bloating
- Flatulence
- Urticaria
- Generally patients are afebrile
Differential Diagnosis
Acute diarrhea
Infectious
- Viral (e.g. rotavirus)
- Bacterial
- Campylobacter
- Shigella
- Salmonella (non-typhi)
- Escherichia coli
- E. coli 0157:H7
- Yersinia enterocolitica
- Vibrio cholerae
- Clostridium difficile
- Parasitic
- Toxin
Noninfectious
- GI Bleed
- Appendicitis
- Mesenteric Ischemia
- Diverticulitis
- Adrenal Crisis
- Thyroid Storm
- Toxicologic exposures
- Antibiotic or drug-associated
Watery Diarrhea
- Enterotoxigenic E. coli (most common cause of watery diarrhea)[3]
- Norovirus (often has prominent vomiting)
- Campylobacter
- Non-typhoidal Salmonella
- Enteroaggregative E. coli (EAEC)
- Enterotoxigenic Bacteroides fragilis
Traveler's Diarrhea
Evaluation
- Stool examination via light microscopy of stained smears or wet mounts
- Stool culture [4]
- ELISA targeted at serum antibodies to Blastocystis species [5]
- PCR [6]
- 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) [7]
- 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
- ↑ 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
- ↑ Blastocystis hominis: commensal or pathogen? Lancet. 1991 Mar 2;337(8740):521-2. PMID: 1671894.
- ↑ Marx et al. “Cholera and Gastroenteritis caused by Noncholera Vibrio Species”. Rosen’s Emergency Medicine 8th edition vol 1 pg 1245-1246.
- ↑ 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
- ↑ 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.
- ↑ 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
- ↑ 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